W3C

HTML 5

W3C Editor's Draft 28 June 2007

This Version:
http://www.w3.org/TR/2007/WD-html5-2007MMDD/
Latest Published Version:
http://www.w3.org/TR/html5/
Latest Editor's Draft:
http://www.w3.org/html/wg/html5/
Editors:
Ian Hickson, Google, Inc.
David Hyatt, Apple, Inc.

Abstract

This specification defines the 5th major revision of the core language of the World Wide Web, HTML. In this version, new features are introduced to help Web application authors, new elements are introduced based on research into prevailing authoring practices, and special attention has been given to defining clear conformance criteria for user agents in an effort to improve interoperability.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

If you wish to make comments regarding this document, please send them to public-html@w3.org (subscribe, archives) or whatwg@whatwg.org (subscribe, archives). All feedback is welcome.

Implementors should be aware that this specification is not stable. Implementors who are not taking part in the discussions are likely to find the specification changing out from under them in incompatible ways. Vendors interested in implementing this specification before it eventually reaches the Candidate Recommendation stage should join the aforementioned mailing lists and take part in the discussions.

The latest stable version of the editor's copy of this specification is always available on the W3C CVS server and in the WHATWG Subversion repository. The latest editor's draft (which may contain unfinished text in the process of being prepared) is available on the WHATWG site. Detailed change history can be obtained from the following locations:

The W3C HTML Working Group is the W3C working group responsible for this specification's progress along the W3C Recommendation track. This specification is the 28 June 2007 Editor's Draft, and has not yet been published as a First Public Working Draft.

This specification is also being produced by the WHATWG. The two specifications are identical from the table of contents onwards.

This specification is intended to replace (be the new version of) what was previously the HTML4, XHTML 1.x, and DOM2 HTML specifications.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Stability

Different parts of this specification are at different levels of maturity.

Known issues are usually marked like this. There are some spec-wide issues that have not yet been addressed: case-sensitivity is a very poorly handled topic right now, and the firing of events needs to be unified (right now some bubble, some don't, they all use different text to fire events, etc).

Table of contents


1. Introduction

This section is non-normative.

The World Wide Web's markup language has always been HTML. HTML was primarily designed as a language for semantically describing scientific documents, although its general design and adaptations over the years has enabled it to be used to describe a number of other types of documents.

The main area that has not been adequately addressed by HTML is a vague subject referred to as Web Applications. This specification attempts to rectify this, while at the same time updating the HTML specifications to address issues raised in the past few years.

1.1. Scope

This section is non-normative.

This specification is limited to providing a semantic-level markup language and associated semantic-level scripting APIs for authoring accessible pages on the Web ranging from static documents to dynamic applications.

The scope of this specification does not include addressing presentation concerns (although default rendering rules for Web browsers are included at the end of this specification).

The scope of this specification does not include documenting every HTML or DOM feature supported by Web browsers. Browsers support many features that are considered to be very bad for accessibility or that are otherwise inappropriate. For example, the blink element is clearly presentational and authors wishing to cause text to blink should instead use CSS.

The scope of this specification is not to describe an entire operating system. In particular, hardware configuration software, image manipulation tools, and applications that users would be expected to use with high-end workstations on a daily basis are out of scope. In terms of applications, this specification is targeted specifically at applications that would be expected to be used by users on an occasional basis, or regularly but from disparate locations, with low CPU requirements. For instance online purchasing systems, searching systems, games (especially multiplayer online games), public telephone books or address books, communications software (e-mail clients, instant messaging clients, discussion software), document editing software, etc.

For sophisticated cross-platform applications, there already exist several proprietary solutions (such as Mozilla's XUL and Macromedia's Flash). These solutions are evolving faster than any standards process could follow, and the requirements are evolving even faster. These systems are also significantly more complicated to specify, and are orders of magnitude more difficult to achieve interoperability with, than the solutions described in this document. Platform-specific solutions for such sophisticated applications (for example the MacOS X Core APIs) are even further ahead.

1.1.1. Relationship to HTML 4.01, XHTML 1.1, DOM2 HTML

This section is non-normative.

This specification represents a new version of HTML4 and XHTML1, along with a new version of the associated DOM2 HTML API. Migration from HTML4 or XHTML1 to the format and APIs described in this specification should in most cases be straightforward, as care has been taken to ensure that backwards-compatibility is retained.

This specification will eventually supplant Web Forms 2.0 as well. [WF2]

1.1.2. Relationship to XHTML2

This section is non-normative.

XHTML2 [XHTML2] defines a new HTML vocabulary with better features for hyperlinks, multimedia content, annotating document edits, rich metadata, declarative interactive forms, and describing the semantics of human literary works such as poems and scientific papers.

However, it lacks elements to express the semantics of many of the non-document types of content often seen on the Web. For instance, forum sites, auction sites, search engines, online shops, and the like, do not fit the document metaphor well, and are not covered by XHTML2.

This specification aims to extend HTML so that it is also suitable in these contexts.

XHTML2 and this specification use different namespaces and therefore can both be implemented in the same XML processor.

1.1.3. Relationship to XUL, Flash, Silverlight, and other proprietary UI languages

This section is non-normative.

This specification is independent of the various proprietary UI languages that various vendors provide. As an open, vender-neutral language, HTML provides for a solution to the same problems without the risk of vendor lock-in.

1.2. Structure of this specification

This section is non-normative.

This specification is divided into the following important sections:

The DOM
The DOM, or Document Object Model, provides a base for the rest of the specification.
The Semantics
Documents are built from elements. These elements form a tree using the DOM. Each element also has a predefined meaning, which is explained in this section. User agent requirements for how to handle each element are also given, along with rules for authors on how to use the element.
Browsing Contexts
HTML documents do not exist in a vacuum — this section defines many of the features that affect environments that deal with multiple pages, links between pages, and running scripts.
APIs
The Editing APIs: HTML documents can provide a number of mechanisms for users to modify content, which are described in this section.
The Communication APIs: Applications written in HTML often require mechanisms to communicate with remote servers, as well as communicating with other applications from different domains running on the same client.
Repetition Templates: A mechanism to support repeating sections in forms.
The Language Syntax
All of these features would be for naught if they couldn't be represented in a serialised form and sent to other people, and so this section defines the syntax of HTML, along with rules for how to parse HTML.

There are also a couple of appendices, defining shims for WYSIWYG editors, rendering rules for Web browsers, and listing areas that are out of scope for this specification.

1.2.1. How to read this specification

This specification should be read like all other specifications. First, it should be read cover-to-cover, multiple times. Then, it should be read backwards at least once. Then it should be read by picking random sections from the contents list and following all the cross-references.

1.3. Conformance requirements

All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. For readability, these words do not appear in all uppercase letters in this specification. [RFC2119]

This specification describes the conformance criteria for user agents (relevant to implementors) and documents (relevant to authors and authoring tool implementors).

There is no implied relationship between document conformance requirements and implementation conformance requirements. User agents are not free to handle non-conformant documents as they please; the processing model described in this specification applies to implementations regardless of the conformity of the input documents.

User agents fall into several (overlapping) categories with different conformance requirements.

Web browsers and other interactive user agents

Web browsers that support XHTML must process elements and attributes from the HTML namespace found in XML documents as described in this specification, so that users can interact with them, unless the semantics of those elements have been overridden by other specifications.

A conforming XHTML processor would, upon finding an XHTML script element in an XML document, execute the script contained in that element. However, if the element is found within an XSLT transformation sheet (assuming the UA also supports XSLT), then the processor would instead treat the script element as an opaque element that forms part of the transform.

Web browsers that support HTML must process documents labelled as text/html as described in this specification, so that users can interact with them.

Non-interactive presentation user agents

User agents that process HTML and XHTML documents purely to render non-interactive versions of them must comply to the same conformance criteria as Web browsers, except that they are exempt from requirements regarding user interaction.

Typical examples of non-interactive presentation user agents are printers (static UAs) and overhead displays (dynamic UAs). It is expected that most static non-interactive presentation user agents will also opt to lack scripting support.

A non-interactive but dynamic presentation UA would still execute scripts, allowing forms to be dynamically submitted, and so forth. However, since the concept of "focus" is irrelevant when the user cannot interact with the document, the UA would not need to support any of the focus-related DOM APIs.

User agents with no scripting support

Implementations that do not support scripting (or which have their scripting features disabled) are exempt from supporting the events and DOM interfaces mentioned in this specification. For the parts of this specification that are defined in terms of an events model or in terms of the DOM, such user agents must still act as if events and the DOM were supported.

Scripting can form an integral part of an application. Web browsers that do not support scripting, or that have scripting disabled, might be unable to fully convey the author's intent.

Conformance checkers

Conformance checkers must verify that a document conforms to the applicable conformance criteria described in this specification. Conformance checkers are exempt from detecting errors that require interpretation of the author's intent (for example, while a document is non-conforming if the content of a blockquote element is not a quote, conformance checkers do not have to check that blockquote elements only contain quoted material).

Conformance checkers must check that the input document conforms when scripting is disabled, and should also check that the input document conforms when scripting is enabled. (This is only a "SHOULD" and not a "MUST" requirement because it has been proven to be impossible. [HALTINGPROBLEM])

The term "HTML5 validator" can be used to refer to a conformance checker that itself conforms to the applicable requirements of this specification.

XML DTDs cannot express all the conformance requirements of this specification. Therefore, a validating XML processor and a DTD cannot constitute a conformance checker. Also, since neither of the two authoring formats defined in this specification are applications of SGML, a validating SGML system cannot constitute a conformance checker either.

To put it another way, there are three types of conformance criteria:

  1. Criteria that can be expressed in a DTD.
  2. Criteria that cannot be expressed by a DTD, but can still be checked by a machine.
  3. Criteria that can only be checked by a human.

A conformance checker must check for the first two. A simple DTD-based validator only checks for the first class of errors and is therefore not a conforming conformance checker according to this specification.

Data mining tools

Applications and tools that process HTML and XHTML documents for reasons other than to either render the documents or check them for conformance should act in accordance to the semantics of the documents that they process.

A tool that generates document outlines but increases the nesting level for each paragraph and does not increase the nesting level for each section would not be conforming.

Authoring tools and markup generators

Authoring tools and markup generators must generate conforming documents. Conformance criteria that apply to authors also apply to authoring tools, where appropriate.

Authoring tools are exempt from the strict requirements of using elements only for their specified purpose, but only to the extent that authoring tools are not yet able to determine author intent.

For example, it is not conforming to use an address element for arbitrary contact information; that element can only be used for marking up contact information for the author of the document or section. However, since an authoring tools is likely unable to determine the difference, an authoring tool is exempt from that requirement.

In terms of conformance checking, an editor is therefore required to output documents that conform to the same extent that a conformance checker will verify.

When an authoring tool is used to edit a non-conforming document, it may preserve the conformance errors in sections of the document that were not edited during the editing session (i.e. an editing tool is allowed to round-trip errorneous content). However, an authoring tool must not claim that the output is conformant if errors have been so preserved.

Authoring tools are expected to come in two broad varieties: tools that work from structure or semantic data, and tools that work on a What-You-See-Is-What-You-Get media-specific editing basis (WYSIWYG).

The former is the preferred mechanism for tools that author HTML, since the structure in the source information can be used to make informed choices regarding which HTML elements and attributes are most appropriate.

However, WYSIWYG tools are legitimate, and this specification makes certain concessions to WYSIWYG editors.

All authoring tools, whether WYSIWYG or not, should make a best effort attempt at enabling users to create well-structured, semantically rich, media-independent content.

Some conformance requirements are phrased as requirements on elements, attributes, methods or objects. Such requirements fall into two categories; those describing content model restrictions, and those describing implementation behaviour. The former category of requirements are requirements on documents and authoring tools. The second category are requirements on user agents.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

User agents may impose implementation-specific limits on otherwise unconstrained inputs, e.g. to prevent denial of service attacks, to guard against running out of memory, or to work around platform-specific limitations.

For compatibility with existing content and prior specifications, this specification describes two authoring formats: one based on XML (referred to as XHTML5), and one using a custom format inspired by SGML (referred to as HTML5). Implementations may support only one of these two formats, although supporting both is encouraged.

XHTML documents (XML documents using elements from the HTML namespace) that use the new features described in this specification and that are served over the wire (e.g. by HTTP) must be sent using an XML MIME type such as application/xml or application/xhtml+xml and must not be served as text/html. [RFC3023]

Such XML documents may contain a DOCTYPE if desired, but this is not required to conform to this specification.

According to the XML specification, XML processors are not guaranteed to process the external DTD subset referenced in the DOCTYPE. This means, for example, that using entities for characters in XHTML documents is unsafe (except for <, >, &, " and '). For interoperability, authors are advised to avoid optional features of XML.

HTML documents, if they are served over the wire (e.g. by HTTP) must be labelled with the text/html MIME type.

The language in this specification assumes that the user agent expands all entity references, and therefore does not include entity reference nodes in the DOM. If user agents do include entity reference nodes in the DOM, then user agents must handle them as if they were fully expanded when implementing this specification. For example, if a requirement talks about an element's child text nodes, then any text nodes that are children of an entity reference that is a child of that element would be used as well.

1.3.1. Common conformance requirements for APIs exposed to JavaScript

A lot of arrays/lists/collections in this spec assume zero-based indexes but use the term "indexth" liberally. We should define those to be zero-based and be clearer about this.

Unless other specified, if a DOM attribute that is a floating point number type (float) is assigned an Infinity or Not-a-Number value, a NOT_SUPPORTED_ERR exception must be raised.

Unless other specified, if a DOM attribute that is a signed numeric type is assigned a negative value, a NOT_SUPPORTED_ERR exception must be raised.

Unless other specified, if a method with an argument that is a floating point number type (float) is passed an Infinity or Not-a-Number value, a NOT_SUPPORTED_ERR exception must be raised.

Unless other specified, if a method is passed fewer arguments than is defined for that method in its IDL definition, a NOT_SUPPORTED_ERR exception must be raised.

Unless other specified, if a method is passed more arguments than is defined for that method in its IDL definition, the excess arguments must be ignored.

Unless other specified, if a method is expecting, as one of its arguments, as defined by its IDL definition, an object implementing a particular interface X, and the argument passed is an object whose [[Class]] property is neither that interface X, nor the name of an interface Y where this specification requires that all objects implementing interface Y also implement interface X, nor the name of an interface that inherits from the expected interface X, then a TYPE_MISMATCH_ERR exception must be raised.

Anything else? Passing the wrong type of object, maybe? Implied conversions to int/float?

1.3.2. Dependencies

This specification relies on several other underlying specifications.

XML

Implementations that support XHTML5 must support some version of XML, as well as its corresponding namespaces specification, because XHTML5 uses an XML serialisation with namespaces. [XML] [XMLNAMES]

XML Base

User agents must follow the rules given by XML Base to resolve relative URIs in HTML and XHTML fragments. That is the mechanism used in this specification for resolving relative URIs in DOM trees. [XMLBASE]

It is possible for xml:base attributes to be present even in HTML fragments, as such attributes can be added dynamically using script.

DOM

Implementations must support some version of DOM Core and DOM Events, because this specification is defined in terms of the DOM, and some of the features are defined as extensions to the DOM Core interfaces. [DOM3CORE] [DOM3EVENTS]

ECMAScript

Implementations that use ECMAScript to implement the APIs defined in this specification must implement them in a manner consistent with the ECMAScript Bindings for DOM Specifications specification, as this specification uses that specification's terminology. [EBFD]

This specification does not require support of any particular network transport protocols, image formats, audio formats, video formats, style sheet language, scripting language, or any of the DOM and WebAPI specifications beyond those described above. However, the language described by this specification is biased towards CSS as the styling language, ECMAScript as the scripting language, and HTTP as the network protocol, and several features assume that those languages and protocols are in use.

1.3.3. Features defined in other specifications

Some elements are defined in terms of their DOM textContent attribute. This is an attribute defined on the Node interface in DOM3 Core. [DOM3CORE]

Should textContent be defined differently for dir="" and <bdo>? Should we come up with an alternative to textContent that handles those and other things, like alt=""?

The term activation behavior is used as defined in the DOM3 Events specification. [DOM3EVENTS] At the time of writing, DOM3 Events hadn't yet been updated to define that phrase.

The rules for handling alternative style sheets are defined in the CSS object model specification. [CSSOM]

See http://dev.w3.org/cvsweb/~checkout~/csswg/cssom/Overview.html?rev=1.35&content-type=text/html;%20charset=utf-8

Certain features are defined in terms of CSS <color> values. When the CSS value currentColor is specified in this context, the "computed value of the 'color' property" for the purposes of determining the computed value of the currentColor keyword is the computed value of the 'color' property on the element in question. [CSS3COLOR]

If a canvas gradient's addColorStop() method is called with the currentColor keyword as the color, then the computed value of the 'color' property on the canvas element is the one that is used.

1.4. Terminology

This specification refers to both HTML and XML attributes and DOM attributes, often in the same context. When it is not clear which is being referred to, they are referred to as content attributes for HTML and XML attributes, and DOM attributes for those from the DOM. Similarly, the term "properties" is used for both ECMAScript object properties and CSS properties. When these are ambiguous they are qualified as object properties and CSS properties respectively.

To ease migration from HTML to XHTML, UAs conforming to this specification will place elements in HTML in the http://www.w3.org/1999/xhtml namespace, at least for the purposes of the DOM and CSS. The term "elements in the HTML namespace", or "HTML elements" for short, when used in this specification, thus refers to both HTML and XHTML elements.

Unless otherwise stated, all elements defined or mentioned in this specification are in the http://www.w3.org/1999/xhtml namespace, and all attributes defined or mentioned in this specification have no namespace (they are in the per-element partition).

The term HTML documents is sometimes used in contrast with XML documents to mean specifically documents that were parsed using an HTML parser (as opposed to using an XML parser or created purely through the DOM).

Generally, when the specification states that a feature applies to HTML or XHTML, it also includes the other. When a feature specifically only applies to one of the two languages, it is called out by explicitly stating that it does not apply to the other format, as in "for HTML, ... (this does not apply to XHTML)".

This specification uses the term document to refer to any use of HTML, ranging from short static documents to long essays or reports with rich multimedia, as well as to fully-fledged interactive applications.

For readability, the term URI is used to refer to both ASCII URIs and Unicode IRIs, as those terms are defined by [RFC3986] and [RFC3987] respectively. On the rare occasions where IRIs are not allowed but ASCII URIs are, this is called out explicitly.

The term root element, when not qualified to explicitly refer to the document's root element, means the furthest ancestor element node of whatever node is being discussed, or the node itself is there is none. When the node is a part of the document, then that is indeed the document's root element. However, if the node is not currently part of the document tree, the root element will be an orphaned node.

An element is said to have been inserted into a document when its root element changes and is now the document's root element.

The term tree order means a pre-order, depth-first traversal of DOM nodes involved (through the parentNode/childNodes relationship).

When it is stated that some element or attribute is ignored, or treated as some other value, or handled as if it was something else, this refers only to the processing of the node after it is in the DOM. A user agent must not mutate the DOM in such situations.

When an XML name, such as an attribute or element name, is referred to in the form prefix:localName, as in xml:id or svg:rect, it refers to a name with the local name localName and the namespace given by the prefix, as defined by the following table:

xml
http://www.w3.org/XML/1998/namespace
html
http://www.w3.org/1999/xhtml
svg
http://www.w3.org/2000/svg

For simplicity, terms such as shown, displayed, and visible might sometimes be used when referring to the way a document is rendered to the user. These terms are not meant to imply a visual medium; they must be considered to apply to other media in equivalent ways.

Various DOM interfaces are defined in this specification using pseudo-IDL. This looks like OMG IDL but isn't. For instance, method overloading is used, and types from the W3C DOM specifications are used without qualification. Language-specific bindings for these abstract interface definitions must be derived in the way consistent with W3C DOM specifications. Some interface-specific binding information for ECMAScript is included in this specification.

The current situation with IDL blocks is pitiful. IDL is totally inadequate to properly represent what objects have to look like in JS; IDL can't say if a member is enumerable, what the indexing behaviour is, what the stringification behaviour is, what behaviour setting a member whose type is a particular interface should be (e.g. setting of document.location or element.className), what constructor an object implementing an interface should claim to have, how overloads work, etc. I think we should make the IDL blocks non-normative, and/or replace them with something else that is better for JS while still being clear on how it applies to other languages. However, we do need to have something that says what types the methods take as arguments, since we have to raise exceptions if they are wrong.

The construction "a Foo object", where Foo is actually an interface, is sometimes used instead of the more accurate "an object implementing the interface Foo".

A DOM attribute is said to be getting when its value is being retrieved (e.g. by author script), and is said to be setting when a new value is assigned to it.

If a DOM object is said to be live, then that means that any attributes returning that object must always return the same object (not a new object each time), and the attributes and methods on that object must operate on the actual underlying data, not a snapshot of the data.

The terms fire and dispatch are used interchangeably in the context of events, as in the DOM Events specifications. [DOM3EVENTS]

The term text node refers to any Text node, including CDATASection nodes (any Node with node type 3 or 4).

Some of the algorithms in this specification, for historical reasons, require the user agent to pause until some condition has been met. While a user agent is paused, it must ensure that no scripts execute (e.g. no event handlers, no timers, etc). User agents should remain responsive to user input while paused, however.

1.4.1. HTML vs XHTML

This section is non-normative.

This specification defines an abstract language for describing documents and applications, and some APIs for interacting with in-memory representations of resources that use this language.

The in-memory representation is known as "DOM5 HTML", or "the DOM" for short.

There are various concrete syntaxes that can be used to transmit resources that use this abstract language, two of which are defined in this specification.

The first such concrete syntax is "HTML5". This is the format recommended for most authors. It is compatible with all legacy Web browsers. If a document is transmitted with the MIME type text/html, then it will be processed as an "HTML5" document by Web browsers.

The second concrete syntax uses XML, and is known as "XHTML5". When a document is transmitted with an XML MIME type, such as application/xhtml+xml, then it is processed by an XML processor by Web browsers, and treated as an "XHTML5" document. Generally speaking, authors are discouraged from trying to use XML on the Web, because XML has much stricter syntax rules than the "HTML5" variant described above, and is relatively newer and therefore less mature.

The "DOM5 HTML", "HTML5", and "XHTML5" representations cannot all represent the same content. For example, namespaces cannot be represented using "HTML5", but they are supported in "DOM5 HTML" and "XHTML5". Similarly, documents that use the noscript feature can be represented using "HTML5", but cannot be represented with "XHTML5" and "DOM5 HTML". Comments that contain the string "-->" can be represented in "DOM5 HTML" but not in "HTML5" and "XHTML5". And so forth.

2. The Document Object Model

The Document Object Model (DOM) is a representation — a model — of a document and its content. [DOM3CORE] The DOM is not just an API; the conformance criteria of HTML implementations are defined, in this specification, in terms of operations on the DOM.

This specification defines the language represented in the DOM by features together called DOM5 HTML. DOM5 HTML consists of DOM Core Document nodes and DOM Core Element nodes, along with text nodes and other content.

Elements in the DOM represent things; that is, they have intrinsic meaning, also known as semantics.

For example, a p element represents a paragraph.

In addition, documents and elements in the DOM host APIs that extend the DOM Core APIs, providing new features to application developers using DOM5 HTML.

2.1. Documents

Every XML and HTML document in an HTML UA is represented by a Document object. [DOM3CORE]

Document objects are assumed to be XML documents unless they are flagged as being HTML documents when they are created. Whether a document is an HTML document or an XML document affects the behaviour of certain APIs, as well as a few CSS rendering rules. [CSS21]

A Document object created by the createDocument() API on the DOMImplementation object is initially an XML document, but can be made into an HTML document by calling document.open() on it.

All Document objects (in user agents implementing this specification) must also implement the HTMLDocument interface, available using binding-specific methods. (This is the case whether or not the document in question is an HTML document or indeed whether it contains any HTML elements at all.) Document objects must also implement the document-level interface of any other namespaces found in the document that the UA supports. For example, if an HTML implementation also supports SVG, then the Document object must implement HTMLDocument and SVGDocument.

Because the HTMLDocument interface is now obtained using binding-specific casting methods instead of simply being the primary interface of the document object, it is no longer defined as inheriting from Document.

interface HTMLDocument {
  // Resource metadata management
  readonly attribute Location location;
  readonly attribute DOMString URL;
           attribute DOMString domain;
  readonly attribute DOMString referrer;
           attribute DOMString cookie;
  readonly attribute DOMString lastModified;
  readonly attribute DOMString compatMode;

  // DOM tree accessors
           attribute DOMString title;
           attribute DOMString dir;
           attribute HTMLElement body;
  readonly attribute HTMLCollection images;
  readonly attribute HTMLCollection links;
  readonly attribute HTMLCollection forms;
  readonly attribute HTMLCollection anchors;
  NodeList getElementsByName(in DOMString elementName);
  NodeList getElementsByClassName(in DOMString[] classNames);

  // Dynamic markup insertion
           attribute DOMString innerHTML;
  void open();
  void open(in DOMString type);
  void open(in DOMString type, in DOMString replace);
  void open(in DOMString url, in DOMString name, in DOMString features);
  void open(in DOMString url, in DOMString name, in DOMString features, in bool replace);
  void close();
  void write(in DOMString text);
  void writeln(in DOMString text);

  // Interaction
  readonly attribute Element activeElement;
  readonly attribute boolean hasFocus;

  // Commands
  readonly attribute HTMLCollection commands;

  // Editing
           attribute boolean designMode;
  boolean execCommand(in DOMString commandId);
  boolean execCommand(in DOMString commandId, in boolean doShowUI);
  boolean execCommand(in DOMString commandId, in boolean doShowUI, in DOMString value);
  Selection getSelection();

  // Cross-document messaging
  void postMessage(in DOMString message);

};

Since the HTMLDocument interface holds methods and attributes related to a number of disparate features, the members of this interface are described in various different sections.

2.1.1. Security

User agents must raise a security exception whenever any of the members of an HTMLDocument object are accessed by scripts whose origin is not the same as the Document's origin, with the following exceptions:

We may want to just put postMessage on Window instead of Document, as that reduces the XSS risk.

2.1.2. Resource metadata management

The URL attribute must return the document's address.

The domain attribute must be initialised to the document's domain, if it has one, and null otherwise. On getting, the attribute must return its current value. On setting, if the new value is an allowed value (as defined below), the attribute's value must be changed to the new value. If the new value is not an allowed value, then a security exception must be raised instead.

A new value is an allowed value for the document.domain attribute if it is equal to the attribute's current value, or if the new value, prefixed by a U+002E FULL STOP ("."), exactly matches the end of the current value. If the current value is null, new values other than null will never be allowed.

If the Document object's address is hierarchical and uses a server-based naming authority, then its domain is the <hostname> part of that address. Otherwise, it has no domain.

The domain attribute is used to enable pages on different hosts of a domain to access each others' DOMs, though this is not yet defined by this specification.

The referrer attribute must return either the URI of the page which navigated the browsing context to the current document (if any), or the empty string (if there is no such originating page, or if the UA has been configured not to report referrers).

In the case of HTTP, the referrer DOM attribute will match the Referer (sic) header that was sent when fetching the current page.

The cookie attribute must, on getting, return the same string as the value of the Cookie HTTP header it would include if fetching the resource indicated by the document's address over HTTP, as per RFC 2109 section 4.3.4. [RFC2109]

On setting, the cookie attribute must cause the user agent to act as it would when processing cookies if it had just attempted to fetch the document's address over HTTP, and had received a response with a Set-Cookie header whose value was the specified value, as per RFC 2109 sections 4.3.1, 4.3.2, and 4.3.3. [RFC2109]

Since the cookie attribute is accessible across frames, the path restrictions on cookies are only a tool to help manage which cookies are sent to which parts of the site, and are not in any way a security feature.

The lastModified attribute, on getting, must return the date and time of the Document's source file's last modification, in the user's local timezone, in the following format:

  1. The month component of the date.
  2. A U+002F SOLIDUS character ('/').
  3. The day component of the date.
  4. A U+002F SOLIDUS character ('/').
  5. The year component of the date.
  6. A U+0020 SPACE character.
  7. The hours component of the time.
  8. A U+003A COLON character (':').
  9. The minutes component of the time.
  10. A U+003A COLON character (':').
  11. The seconds component of the time.

All the numeric components above, other than the year, must be given as two digits in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE representing the number in base ten, zero-padded if necessary.

The Document's source file's last modification date and time must be derived from relevant features of the networking protocols used, e.g. from the value of the HTTP Last-Modified header of the document, or from metadata in the filesystem for local files. If the last modification date and time are not known, the attribute must return the string 01/01/1970 00:00:00.

The compatMode DOM attribute must return the literal string "CSS1Compat" unless the document has been set to quirks mode by the HTML parser, in which case it must instead return the literal string "BackCompat". The document can also be set to limited quirks mode (also known as "almost standards" mode). By default, the document is set to no quirks mode (also known as "standards mode").

As far as parsing goes, the quirks I know of are:

2.2. Elements

The nodes representing HTML elements in the DOM must implement, and expose to scripts, the interfaces listed for them in the relevant sections of this specification. This includes XHTML elements in XML documents, even when those documents are in another context (e.g. inside an XSLT transform).

The basic interface, from which all the HTML elements' interfaces inherit, and which must be used by elements that have no additional requirements, is the HTMLElement interface.

interface HTMLElement : Element {
  // DOM tree accessors
  NodeList getElementsByClassName(in DOMString[] classNames);

  // Dynamic markup insertion
           attribute DOMString innerHTML;

  // Metadata attributes
           attribute DOMString id;
           attribute DOMString title;
           attribute DOMString lang;
           attribute DOMString dir;
           attribute DOMString className;
  readonly attribute DOMTokenList classList;

  // Interaction
           attribute boolean irrelevant;
           attribute long tabIndex;
  void click();
  void focus();
  void blur();
  void scrollIntoView();
  void scrollIntoView(in boolean top);

  // Commands
           attribute HTMLMenuElement contextMenu;

  // Editing
           attribute boolean draggable;
           attribute DOMString contentEditable;

  // event handler DOM attributes
           attribute EventListener onabort;
           attribute EventListener onbeforeunload;
           attribute EventListener onblur;
           attribute EventListener onchange;
           attribute EventListener onclick;
           attribute EventListener oncontextmenu;
           attribute EventListener ondblclick;
           attribute EventListener ondrag;
           attribute EventListener ondragend;
           attribute EventListener ondragenter;
           attribute EventListener ondragleave;
           attribute EventListener ondragover;
           attribute EventListener ondragstart;
           attribute EventListener ondrop;
           attribute EventListener onerror;
           attribute EventListener onfocus;
           attribute EventListener onkeydown;
           attribute EventListener onkeypress;
           attribute EventListener onkeyup;
           attribute EventListener onload;
           attribute EventListener onmessage;
           attribute EventListener onmousedown;
           attribute EventListener onmousemove;
           attribute EventListener onmouseout;
           attribute EventListener onmouseover;
           attribute EventListener onmouseup;
           attribute EventListener onmousewheel;
           attribute EventListener onresize;
           attribute EventListener onscroll;
           attribute EventListener onselect;
           attribute EventListener onsubmit;
           attribute EventListener onunload;

};

As with the HTMLDocument interface, the HTMLElement interface holds methods and attributes related to a number of disparate features, and the members of this interface are therefore described in various different sections of this specification.

2.2.1. Reflecting content attributes in DOM attributes

Some DOM attributes are defined to reflect a particular content attribute. This means that on getting, the DOM attribute returns the current value of the content attribute, and on setting, the DOM attribute changes the value of the content attribute to the given value.

If a reflecting DOM attribute is a DOMString attribute whose content attribute is defined to contain a URI, then on getting, the DOM attribute must return the value of the content attribute, resolved to an absolute URI, and on setting, must set the content attribute to the specified literal value. If the content attribute is absent, the DOM attribute must return the default value, if the content attribute has one, or else the empty string.

If a reflecting DOM attribute is a DOMString whose content attribute is an enumerated attribute, and the DOM attribute is limited to only known values, then, on getting, the DOM attribute must return the value associated with the state the attribute is in (in its canonical case), or the empty string if the attribute is in a state that has no associated keyword value; and on setting, if the new value case-insensitively matches one of the keywords given for that attribute, then the content attribute must be set to that value, otherwise, if the new value is the empty string, then the content attribute must be removed, otherwise, the setter must raise a SYNTAX_ERR exception.

If a reflecting DOM attribute is a DOMString but doesn't fall into any of the above categories, then the getting and setting must be done in a transparent, case-preserving manner.

If a reflecting DOM attribute is a boolean attribute, then the DOM attribute must return true if the attribute is set, and false if it is absent. On setting, the content attribute must be removed if the DOM attribute is set to false, and must be set to have the same value as its name if the DOM attribute is set to true. (This corresponds to the rules for boolean content attributes.)

If a reflecting DOM attribute is a signed integer type (long) then the content attribute must be parsed according to the rules for parsing signed integers first. If that fails, or if the attribute is absent, the default value must be returned instead, or 0 if there is no default value. On setting, the given value must be converted to a string representing the number as a valid integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is an unsigned integer type (unsigned long) then the content attribute must be parsed according to the rules for parsing unsigned integers first. If that fails, or if the attribute is absent, the default value must be returned instead, or 0 if there is no default value. On setting, the given value must be converted to a string representing the number as a valid non-negative integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is an unsigned integer type (unsigned long) that is limited to only positive non-zero numbers, then the behavior is similar to the previous case, but zero is not allowed. On getting, the content attribute must first be parsed according to the rules for parsing unsigned integers, and if that fails, or if the attribute is absent, the default value must be returned instead, or 1 if there is no default value. On setting, if the value is zero, the user agent must fire an INDEX_SIZE_ERR exception. Otherwise, the given value must be converted to a string representing the number as a valid non-negative integer in base ten and then that string must be used as the new content attribute value.

If a reflecting DOM attribute is a floating point number type (float) and the content attribute is defined to contain a time offset, then the content attribute must be parsed according to the rules for parsing time ofsets first. If that fails, or if the attribute is absent, the default value must be returned instead, or the not-a-number value (NaN) if there is no default value. On setting, the given value must be converted to a string using the time offset serialisation rules, and that string must be used as the new content attribute value.

If a reflecting DOM attribute is of the type DOMTokenList, then on getting it must return a DOMTokenList object whose underlying string is the element's corresponding content attribute. When the DOMTokenList object mutates its underlying string, the attribute must itself be immediately mutated. When the attribute is absent, then the string represented by the DOMTokenList object is the empty string; when the object mutates this empty string, the user agent must first add the corresponding content attribute, and then mutate that attribute instead. DOMTokenList attributes are always read-only. The same DOMTokenList object must be returned every time for each attribute.

If a reflecting DOM attribute has the type HTMLElement, or an interface that descends from HTMLElement, then, on getting, it must run the following algorithm (stopping at the first point where a value is returned):

  1. If the corresponding content attribute is absent, then the DOM attribute must return null.
  2. Let candidate be the element that the document.getElementById() method would find if it was passed as its argument the current value of the corresponding content attribute.
  3. If candidate is null, or if it is not type-compatible with the DOM attribute, then the DOM attribute must return null.
  4. Otherwise, it must return candidate.

On setting, if the given element has an id attribute, then the content attribute must be set to the value of that id attribute. Otherwise, the DOM attribute must be set to the empty string.

2.3. Common DOM interfaces

2.3.1. Collections

The HTMLCollection, HTMLFormControlsCollection, and HTMLOptionsCollection interfaces represent various lists of DOM nodes. Collectively, objects implementing these interfaces are called collections.

When a collection is created, a filter and a root are associated with the collection.

For example, when the HTMLCollection object for the document.images attribute is created, it is associated with a filter that selects only img elements, and rooted at the root of the document.

The collection then represents a live view of the subtree rooted at the collection's root, containing only nodes that match the given filter. The view is linear. In the absence of specific requirements to the contrary, the nodes within the collection must be sorted in tree order.

The rows list is not in tree order.

An attribute that returns a collection must return the same object every time it is retrieved.

2.3.1.1. HTMLCollection

The HTMLCollection interface represents a generic collection of elements.

interface HTMLCollection {
  readonly attribute unsigned long length;
  Element item(in unsigned long index);
  Element namedItem(in DOMString name);
};

The length attribute must return the number of nodes represented by the collection.

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The namedItem(key) method must return the first node in the collection that matches the following requirements:

If no such elements are found, then the method must return null.

In ECMAScript implementations, objects that implement the HTMLCollection interface must also have a [[Get]] method that, when invoked with a property name that is a number, acts like the item() method would when invoked with that argument, and when invoked with a property name that is a string, acts like the namedItem() method would when invoked with that argument.

2.3.1.2. HTMLFormControlsCollection

The HTMLFormControlsCollection interface represents a collection of form controls.

interface HTMLFormControlsCollection {
  readonly attribute unsigned long length;
  HTMLElement item(in unsigned long index);
  Object namedItem(in DOMString name);
};

The length attribute must return the number of nodes represented by the collection.

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The namedItem(key) method must act according to the following algorithm:

  1. If, at the time the method is called, there is exactly one node in the collection that has either an id attribute or a name attribute equal to key, then return that node and stop the algorithm.
  2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to key, then return null and stop the algorithm.
  3. Otherwise, create a NodeList object representing a live view of the HTMLFormControlsCollection object, further filtered so that the only nodes in the NodeList object are those that have either an id attribute or a name attribute equal to key. The nodes in the NodeList object must be sorted in tree order.
  4. Return that NodeList object.

In the ECMAScript DOM binding, objects implementing the HTMLFormControlsCollection interface must support being dereferenced using the square bracket notation, such that dereferencing with an integer index is equivalent to invoking the item() method with that index, and such that dereferencing with a string index is equivalent to invoking the namedItem() method with that index.

2.3.1.3. HTMLOptionsCollection

The HTMLOptionsCollection interface represents a list of option elements.

interface HTMLOptionsCollection {
           attribute unsigned long length;
  HTMLOptionElement item(in unsigned long index);
  Object namedItem(in DOMString name);
};

On getting, the length attribute must return the number of nodes represented by the collection.

On setting, the behaviour depends on whether the new value is equal to, greater than, or less than the number of nodes represented by the collection at that time. If the number is the same, then setting the attribute must do nothing. If the new value is greater, then n new option elements with no attributes and no child nodes must be appended to the select element on which the HTMLOptionsCollection is rooted, where n is the difference between the two numbers (new value minus old value). If the new value is lower, then the last n nodes in the collection must be removed from their parent nodes, where n is the difference between the two numbers (old value minus new value).

Setting length never removes or adds any optgroup elements, and never adds new children to existing optgroup elements (though it can remove children from them).

The item(index) method must return the indexth node in the collection. If there is no indexth node in the collection, then the method must return null.

The namedItem(key) method must act according to the following algorithm:

  1. If, at the time the method is called, there is exactly one node in the collection that has either an id attribute or a name attribute equal to key, then return that node and stop the algorithm.
  2. Otherwise, if there are no nodes in the collection that have either an id attribute or a name attribute equal to key, then return null and stop the algorithm.
  3. Otherwise, create a NodeList object representing a live view of the HTMLOptionsCollection object, further filtered so that the only nodes in the NodeList object are those that have either an id attribute or a name attribute equal to key. The nodes in the NodeList object must be sorted in tree order.
  4. Return that NodeList object.

In the ECMAScript DOM binding, objects implementing the HTMLOptionsCollection interface must support being dereferenced using the square bracket notation, such that dereferencing with an integer index is equivalent to invoking the item() method with that index, and such that dereferencing with a string index is equivalent to invoking the namedItem() method with that index.

We may want to add add() and remove() methods here too because IE implements HTMLSelectElement and HTMLOptionsCollection on the same object, and so people use them almost interchangeably in the wild.

2.3.2. DOMTokenList

The DOMTokenList interface represents an interface to an underlying string that consists of an unordered set of space-separated tokens.

Which string underlies a particular DOMTokenList object is defined when the object is created. It might be a content attribute (e.g. the string that underlies the classList object is the class attribute), or it might be an anonymous string (e.g. when a DOMTokenList object is passed to an author-implemented callback in the datagrid APIs).

interface DOMTokenList {
  readonly attribute unsigned long length;
  DOMString item(in unsigned long index);
  boolean has(in DOMString token);
  void add(in DOMString token);
  void remove(in DOMString token);
  boolean toggle(in DOMString token);
};

The length attribute must return the number of unique tokens that result from splitting the underlying string on spaces.

The item(index) method must split the underlying string on spaces, sort the resulting list of tokens by Unicode codepoint, remove exact duplicates, and then return the indexth item in this list. If index is equal to or greater than the number of tokens, then the method must return null.

In ECMAScript implementations, objects that implement the DOMTokenList interface must also have a [[Get]] method that, when invoked with a property name that is a number, acts like the item() method would when invoked with that argument.

The has(token) method must run the following algorithm:

  1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the token indicated by token is one of the tokens in the object's underlying string then return true and stop this algorithm.
  4. Otherwise, return false.

The add(token) method must run the following algorithm:

  1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the given token is already one of the tokens in the DOMTokenList object's underlying string then stop the algorithm.
  4. Otherwise, if the last character of the DOMTokenList object's underlying string is not a space character, then append a U+0020 SPACE character to the end of that string.
  5. Append the value of token to the end of the DOMTokenList object's underlying string.

The remove(token) method must run the following algorithm:

  1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, remove the given token from the underlying string.

The toggle(token) method must run the following algorithm:

  1. If the token argument contains any spaces, then raise an INVALID_CHARACTER_ERR exception and stop the algorithm.
  2. Otherwise, split the underlying string on spaces to get the list of tokens in the object's underlying string.
  3. If the given token is already one of the tokens in the DOMTokenList object's underlying string then remove the given token from the underlying string, and stop the algorithm, returning false.
  4. Otherwise, if the last character of the DOMTokenList object's underlying string is not a space character, then append a U+0020 SPACE character to the end of that string.
  5. Append the value of token to the end of the DOMTokenList object's underlying string.
  6. Return true.

In the ECMAScript DOM binding, objects implementing the DOMTokenList interface must stringify to the object's underlying string representation.

2.3.3. DOM feature strings

DOM3 Core defines mechanisms for checking for interface support, and for obtaining implementations of interfaces, using feature strings. [DOM3CORE]

A DOM application can use the hasFeature(feature, version) method of the DOMImplementation interface with parameter values "HTML" and "5.0" (respectively) to determine whether or not this module is supported by the implementation. In addition to the feature string "HTML", the feature string "XHTML" (with version string "5.0") can be used to check if the implementation supports XHTML. User agents should respond with a true value when the hasFeature method is queried with these values. Authors are cautioned, however, that UAs returning true might not be perfectly compliant, and that UAs returning false might well have support for features in this specification; in general, therefore, use of this method is discouraged.

The values "HTML" and "XHTML" (both with version "5.0") should also be supported in the context of the getFeature() and isSupported() methods, as defined by DOM3 Core.

The interfaces defined in this specification are not always supersets of the interfaces defined in DOM2 HTML; some features that were formerly deprecated, poorly supported, rarely used or considered unnecessary have been removed. Therefore it is not guarenteed that an implementation that supports "HTML" "5.0" also supports "HTML" "2.0".

2.4. DOM tree accessors

The html element of a document is the document's root element, if there is one and it's an html element, or null otherwise.

The head element of a document is the first head element that is a child of the html element, if there is one, or null otherwise.

The title element of a document is the first title element that is a child of the head element, if there is one, or null otherwise.

The title attribute must, on getting, run the following algorithm:

  1. If the root element is an svg element in the "http://www.w3.org/2000/svg" namespace, and the user agent supports SVG, then the getter must return the value that would have been returned by the DOM attribute of the same name on the SVGDocument interface.

  2. Otherwise, it must return a concatenation of the data of all the child text nodes of the title element, in tree order, or the empty string if the title element is null.

On setting, the following algorithm must be run:

  1. If the root element is an svg element in the "http://www.w3.org/2000/svg" namespace, and the user agent supports SVG, then the setter must defer to the setter for the DOM attribute of the same name on the SVGDocument interface. Stop the algorithm here.

  2. If the head element is null, then the attribute must do nothing. Stop the algorithm here.
  3. If the title element is null, then a new title element must be created and appended to the head element.
  4. The children of the title element (if any) must all be removed.
  5. A single Text node whose data is the new value being assigned must be appended to the title element.

The title attribute on the HTMLDocument interface should shadow the attribute of the same name on the SVGDocument interface when the user agent supports both HTML and SVG.

The body element of a document is the first child of the html element that is either a body element or a frameset element. If there is no such element, it is null. If the body element is null, then when the specification requires that events be fired at "the body element", they must instead be fired at the Document object.

The body attribute, on getting, must return the body element of the document (either a body element, a frameset element, or null). On setting, the following algorithm must be followed:

  1. If the new value is not a body or frameset element, then raise a HIERARCHY_REQUEST_ERR exception and abort these steps.
  2. Otherwise, if the new value is the same as the body element, do nothing. Abort these steps.
  3. Otherwise, if the body element is not null, then replace that element with the new value in the DOM, as if the root element's replaceChild() method had been called with the new value and the incumbent body element as its two arguments respectively, then abort these steps.
  4. Otherwise, the the body element is null. Append the new value to the root element.

The images attribute must return an HTMLCollection rooted at the Document node, whose filter matches only img elements.

The links attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with href attributes and area elements with href attributes.

The forms attribute must return an HTMLCollection rooted at the Document node, whose filter matches only form elements.

The anchors attribute must return an HTMLCollection rooted at the Document node, whose filter matches only a elements with name attributes.

The getElementsByName(name) method a string name, and must return a live NodeList containing all the a, applet, button, form, iframe, img, input, map, meta, object, select, and textarea elements in that document that have a name attribute whose value is equal to the name argument.

The getElementsByClassName(classNames) method takes an array of strings representing classes. When called, the method must return a live NodeList object containing all the elements in the document that have all the classes specified in that array. If the array is empty, then the method must return an empty NodeList.

HTML, XHTML, SVG and MathML elements define which classes they are in by having an attribute in the per-element partition with the name class containing a space-separated list of classes to which the element belongs. Other specifications may also allow elements in their namespaces to be labelled as being in specific classes. UAs must not assume that all attributes of the name class for elements in any namespace work in this way, however, and must not assume that such attributes, when used as global attributes, label other elements as being in specific classes.

Given the following XHTML fragment:

<div id="example">
 <p id="p1" class="aaa bbb"/>
 <p id="p2" class="aaa ccc"/>
 <p id="p3" class="bbb ccc"/>
</div>

A call to document.getElementById('example').getElementsByClassName('aaa') would return a NodeList with the two paragraphs p1 and p2 in it.

A call to getElementsByClassName(['ccc', 'bbb']) would only return one node, however, namely p3. A call to document.getElementById('example').getElementsByClassName('ccc bbb') would return the same thing.

A call to getElementsByClassName(['aaa bbb']) would return no nodes; none of the elements above are in the "aaa bbb" class.

A call to getElementsByClassName(['']) would also return no nodes, since none of the nodes are in the "" class (indeed, in HTML, it is impossible to specify that an element is in the "" class).

The getElementsByClassName() method on the HTMLElement interface must return the nodes that the HTMLDocument getElementsByClassName() method would return, excluding any elements that are not descendants of the HTMLElement object on which the method was invoked.

The dir attribute on the HTMLDocument interface is defined along with the dir content attribute.

2.5. Dynamic markup insertion

The document.write() family of methods and the innerHTML family of DOM attributes enable script authors to dynamically insert markup into the document.

bz argues that innerHTML should be called something else on XML documents and XML elements. Is the sanity worth the migration pain?

Because these APIs interact with the parser, their behaviour varies depending on whether they are used with HTML documents (and the HTML parser) or XHTML in XML documents (and the XML parser). The following table cross-references the various versions of these APIs.

document.write() innerHTML
For documents that are HTML documents document.write() in HTML innerHTML in HTML
For documents that are XML documents document.write() in XML innerHTML in XML

Regardless of the parsing mode, the document.writeln(s) method must call the document.write() method with the same argument s, and then call the document.write() method with, as its argument, a string consisting of a single line feed character (U+000A).

2.5.1. Controlling the input stream

The open() method comes in several variants with different numbers of arguments.

When called with two or fewer arguments, the method must act as follows:

  1. Let type be the value of the first argument, if there is one, or "text/html" otherwise.

  2. Let replace be true if there is a second argument and it has the value "replace", and false otherwise.

  3. If the document has an active parser that isn't a script-created parser, and the insertion point associated with that parser's input stream is not undefined (that is, it does point to somewhere in the input stream), then the method does nothing. Abort these steps.

    This basically causes document.open() to be ignored when it's called in an inline script found during the parsing of data sent over the network, while still letting it have an effect when called asynchronously or on a document that is itself being spoon-fed using these APIs.

  4. onbeforeunload, onunload

  5. If the document has an active parser, then stop that parser, and throw away any pending content in the input stream. what about if it doesn't, because it's either like a text/plain, or Atom, or PDF, or XHTML, or image document, or something?

  6. Remove all child nodes of the document.

  7. Create a new HTML parser and associate it with the document. This is a script-created parser (meaning that it can be closed by the document.open() and document.close() methods, and that the tokeniser will wait for an explicit call to document.close() before emitting an end-of-file token).

  8. Mark the document as being an HTML document (it might already be so-marked).
  9. If type does not have the value "text/html", then act as if the tokeniser had emitted a pre element start tag, then set the HTML parser's tokenisation stage's content model flag to PLAINTEXT.

  10. If replace is false, then:

    1. Remove all the entries in the browsing context's session history after the current entry in its Document's History object
    2. Remove any earlier entries that share the same Document
    3. Add a new entry just before the last entry that is associated with the text that was parsed by the previous parser associated with the Document object, as well as the state of the document at the start of these steps. (This allows the user to step backwards in the session history to see the page before it was blown away by the document.open() call.)
  11. Finally, set the insertion point to point at just before the end of the input stream (which at this point will be empty).

We shouldn't hard-code text/plain there. We should do it some other way, e.g. hand off to the section on content-sniffing and handling of incoming data streams, the part that defines how this all works when stuff comes over the network.

When called with three or more arguments, the open() method on the HTMLDocument object must call the open() method on the Window interface of the object returned by the defaultView attribute of the DocumentView interface of the HTMLDocument object, with the same arguments as the original call to the open() method. If the defaultView attribute of the DocumentView interface of the HTMLDocument object is null, then the method must raise an INVALID_ACCESS_ERR exception.

The close() method must do nothing if there is no script-created parser associated with the document. If there is such a parser, then, when the method is called, the user agent must insert an explicit "EOF" character at the insertion point of the parser's input stream.

2.5.2. Dynamic markup insertion in HTML

In HTML, the document.write(s) method must act as follows:

  1. If the insertion point is undefined, the open() method must be called (with no arguments) on the document object. The insertion point will point at just before the end of the (empty) input stream.

  2. The string s must be inserted into the input stream just before the insertion point.

  3. If there is a script that will execute as soon as the parser resumes, then the method must now return without further processing of the input stream.

  4. Otherwise, the tokeniser must process the characters that were inserted, one at a time, processing resulting tokens as they are emitted, and stopping when the tokeniser reaches the insertion point or when the processing of the tokeniser is aborted by the tree construction stage (this can happen if a script start tag token is emitted by the tokeniser).

    If the document.write() method was called from script executing inline (i.e. executing because the parser parsed a set of script tags), then this is a reentrant invocation of the parser.

  5. Finally, the method must return.

In HTML, the innerHTML DOM attribute of all HTMLElement and HTMLDocument nodes returns a serialisation of the node's children using the HTML syntax. On setting, it replaces the node's children with new nodes that result from parsing the given value. The formal definitions follow.

On getting, the innerHTML DOM attribute must return the result of running the HTML fragment serialisation algorithm on the node.

On setting, if the node is a document, the innerHTML DOM attribute must run the following algorithm:

  1. If the document has an active parser, then stop that parser, and throw away any pending content in the input stream. what about if it doesn't, because it's either like a text/plain, or Atom, or PDF, or XHTML, or image document, or something?

  2. Remove the children nodes of the Document whose innerHTML attribute is being set.

  3. Create a new HTML parser, in its initial state, and associate it with the Document node.

  4. Place into the input stream for the HTML parser just created the string being assigned into the innerHTML attribute.

  5. Start the parser and let it run until it has consumed all the characters just inserted into the input stream. (The Document node will have been populated with elements and a load event will have fired on its body element.)

Otherwise, if the node is an element, then setting the innerHTML DOM attribute must cause the following algorithm to run instead:

  1. Invoke the HTML fragment parsing algorithm, with the element whose innerHTML attribute is being set as the context and the string being assigned into the innerHTML attribute as the input. Let new children be the result of this algorithm.

  2. Remove the children of the element whose innerHTML attribute is being set.

  3. Let target document be the ownerDocument of the Element node whose innerHTML attribute is being set.

  4. Set the ownerDocument of all the nodes in new children to the target document.

  5. Append all the new children nodes to the node whose innerHTML attribute is being set, preserving their order.

script elements inserted using innerHTML do not execute when they are inserted.

2.5.3. Dynamic markup insertion in XML

In an XML context, the document.write(s) method must raise an INVALID_ACCESS_ERR exception.

On the other hand, however, the innerHTML attribute is indeed usable in an XML context.

In an XML context, the innerHTML DOM attribute on HTMLElements and HTMLDocuments, on getting, must return a string in the form of an internal general parsed entity that is XML namespace-well-formed, the string being an isomorphic serialisation of all of that node's child nodes, in document order. User agents may adjust prefixes and namespace declarations in the serialisation (and indeed might be forced to do so in some cases to obtain namespace-well-formed XML). [XML] [XMLNS]

If any of the following cases are found in the DOM being serialised, the user agent must raise an INVALID_STATE_ERR exception:

These are the only ways to make a DOM unserialisable. The DOM enforces all the other XML constraints; for example, trying to set an attribute with a name that contains an equals sign (=) will raised an INVALID_CHARACTER_ERR exception.

On setting, in an XML context, the innerHTML DOM attribute on HTMLElements and HTMLDocuments must run the following algorithm:

  1. The user agent must create a new XML parser.

  2. If the innerHTML attribute is being set on an element, the user agent must feed the parser just created the string corresponding to the start tag of that element, declaring all the namespace prefixes that are in scope on that element in the DOM, as well as declaring the default namespace (if any) that is in scope on that element in the DOM.

  3. The user agent must feed the parser just created the string being assigned into the innerHTML attribute.

  4. If the innerHTML attribute is being set on an element, the user agent must feed the parser the string corresponding to the end tag of that element.

  5. If the parser found a well-formedness error, the attribute's setter must raise a SYNTAX_ERR exception and abort these steps.

  6. The user agent must remove the children nodes of the node whose innerHTML attribute is being set.

  7. If the attribute is being set on a Document node, let new children be the children of the document, preserving their order. Otherwise, the attribute is being set on an Element node; let new children be the children of the the document's root element, preserving their order.

  8. If the attribute is being set on a Document node, let target document be that Document node. Otherwise, the attribute is being set on an Element node; let target document be the ownerDocument of that Element.

  9. Set the ownerDocument of all the nodes in new children to the target document.

  10. Append all the new children nodes to the node whose innerHTML attribute is being set, preserving their order.

script elements inserted using innerHTML do not execute when they are inserted.

2.6. APIs in HTML documents

For HTML documents, and for HTML elements in HTML documents, certain APIs defined in DOM3 Core become case-insensitive or case-changing, as sometimes defined in DOM3 Core, and as summarised or required below. [DOM3CORE].

This does not apply to XML documents or to elements that are not in the HTML namespace despite being in HTML documents.

Element.tagName, Node.nodeName, and Node.localName

These attributes return tag names in all uppercase and attribute names in all lowercase, regardless of the case with which they were created.

Document.createElement()

The canonical form of HTML markup is all-lowercase; thus, this method will lowercase the argument before creating the requisite element. Also, the element created must be in the HTML namespace.

This doesn't apply to Document.createElementNS(). Thus, it is possible, by passing this last method a tag name in the wrong case, to create an element that claims to have the tag name of an HTML element, but doesn't support its interfaces, because it really has another tag name not accessible from the DOM APIs.

Element.setAttributeNode()

When an Attr node is set on an HTML element, it must have its name lowercased before the element is affected.

This doesn't apply to Document.setAttributeNodeNS().

Element.setAttribute()

When an attribute is set on an HTML element, the name argument must be lowercased before the element is affected.

This doesn't apply to Document.setAttributeNS().

Document.getElementsByTagName() and Element.getElementsByTagName()

These methods (but not their namespaced counterparts) must compare the given argument case-insensitively when looking at HTML elements, and case-sensitively otherwise.

Thus, in an HTML document with nodes in multiple namespaces, these methods will be both case-sensitive and case-insensitive at the same time.

Document.renameNode()

If the new namespace is the HTML namespace, then the new qualified name must be lowercased before the rename takes place.

3. Semantics and structure of HTML elements

3.1. Introduction

This section is non-normative.

An introduction to marking up a document.

3.2. Common microsyntaxes

There are various places in HTML that accept particular data types, such as dates or numbers. This section describes what the conformance criteria for content in those formats is, and how to parse them.

Need to go through the whole spec and make sure all the attribute values are clearly defined either in terms of microsyntaxes or in terms of other specs, or as "Text" or some such.

3.2.1. Common parser idioms

The space characters, for the purposes of this specification, are U+0020 SPACE, U+0009 CHARACTER TABULATION (tab), U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), and U+000D CARRIAGE RETURN (CR).

Some of the micro-parsers described below follow the pattern of having an input variable that holds the string being parsed, and having a position variable pointing at the next character to parse in input.

For parsers based on this pattern, a step that requires the user agent to collect a sequence of characters means that the following algorithm must be run, with characters being the set of characters that can be collected:

  1. Let input and position be the same variables as those of the same name in the algorithm that invoked these steps.

  2. Let result be the empty string.

  3. While position doesn't point past the end of input and the character at position is one of the characters, append that character to the end of result and advance position to the next character in input.

  4. Return result.

The step skip whitespace means that the user agent must collect a sequence of characters that are space characters. The step skip Zs characters means that the user agent must collect a sequence of characters that are in the Unicode character class Zs. In both cases, the collected characters are not used. [UNICODE]

3.2.2. Boolean attributes

A number of attributes in HTML5 are boolean attributes. The presence of a boolean attribute on an element represents the true value, and the absence of the attribute represents the false value.

If the attribute is present, its value must either be the empty string or the attribute's canonical name, exactly, with no leading or trailing whitespace, and in lowercase.

3.2.3. Numbers

3.2.3.1. Unsigned integers

A string is a valid non-negative integer if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9).

The rules for parsing non-negative integers are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return zero, a positive integer, or an error. Leading spaces are ignored. Trailing spaces and indeed any trailing garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 0.

  4. Skip whitespace.

  5. If position is past the end of input, return an error.

  6. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  7. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is not past the end of input, return to the top of step 7 in the overall algorithm (that's the step within which these substeps find themselves).
  8. Return value.

3.2.3.2. Signed integers

A string is a valid integer if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally prefixed with a U+002D HYPHEN-MINUS ("-") character.

The rules for parsing integers are similar to the rules for non-negative integers, and are as given in the following algorithm. When invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return an integer or an error. Leading spaces are ignored. Trailing spaces and trailing garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 0.

  4. Let sign have the value "positive".

  5. Skip whitespace.

  6. If position is past the end of input, return an error.

  7. If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS ("-") character:

    1. Let sign be "negative".
    2. Advance position to the next character.
    3. If position is past the end of input, return an error.
  8. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  9. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is not past the end of input, return to the top of step 9 in the overall algorithm (that's the step within which these substeps find themselves).
  10. If sign is "positive", return value, otherwise return 0-value.

3.2.3.3. Real numbers

A string is a valid floating point number if it consists of one of more characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), optionally with a single U+002E FULL STOP (".") character somewhere (either before these numbers, in between two numbers, or after the numbers), all optionally prefixed with a U+002D HYPHEN-MINUS ("-") character.

The rules for parsing floating point number values are as given in the following algorithm. As with the previous algorithms, when this one is invoked, the steps must be followed in the order given, aborting at the first step that returns a value. This algorithm will either return a number or an error. Leading spaces are ignored. Trailing spaces and garbage characters are ignored.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let value have the value 0.

  4. Let sign have the value "positive".

  5. Skip whitespace.

  6. If position is past the end of input, return an error.

  7. If the character indicated by position (the first character) is a U+002D HYPHEN-MINUS ("-") character:

    1. Let sign be "negative".
    2. Advance position to the next character.
    3. If position is past the end of input, return an error.
  8. If the next character is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9) or U+002E FULL STOP ("."), then return an error.

  9. If the next character is U+002E FULL STOP ("."), but either that is the last character or the character after that one is not one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9), then return an error.

  10. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply value by ten.
    2. Add the value of the current character (0..9) to value.
    3. Advance position to the next character.
    4. If position is past the end of input, then if sign is "positive", return value, otherwise return 0-value.
    5. Otherwise return to the top of step 10 in the overall algorithm (that's the step within which these substeps find themselves).
  11. Otherwise, if the next character is not a U+002E FULL STOP ("."), then if sign is "positive", return value, otherwise return 0-value.

  12. The next character is a U+002E FULL STOP ("."). Advance position to the character after that.

  13. Let divisor be 1.

  14. If the next character is one of U+0030 DIGIT ZERO (0) .. U+0039 DIGIT NINE (9):

    1. Multiply divisor by ten.
    2. Add the value of the current character (0..9) divided by divisor, to value.
    3. Advance position to the next character.
    4. If position is past the end of input, then if sign is "positive", return value, otherwise return 0-value.
    5. Otherwise return to the top of step 14 in the overall algorithm (that's the step within which these substeps find themselves).
  15. Otherwise, if sign is "positive", return value, otherwise return 0-value.

3.2.3.4. Ratios

The algorithms described in this section are used by the progress and meter elements.

A valid denominator punctuation character is one of the characters from the table below. There is a value associated with each denominator punctuation character, as shown in the table below.

Denominator Punctuation Character Value
U+0025 PERCENT SIGN % 100
U+066A ARABIC PERCENT SIGN ٪ 100
U+FE6A SMALL PERCENT SIGN 100
U+FF05 FULLWIDTH PERCENT SIGN 100
U+2030 PER MILLE SIGN 1000
U+2031 PER TEN THOUSAND SIGN 10000

The steps for finding one or two numbers of a ratio in a string are as follows:

  1. If the string is empty, then return nothing and abort these steps.
  2. Find a number in the string according to the algorithm below, starting at the start of the string.
  3. If the sub-algorithm in step 2 returned nothing or returned an error condition, return nothing and abort these steps.
  4. Set number1 to the number returned by the sub-algorithm in step 2.
  5. Starting with the character immediately after the last one examined by the sub-algorithm in step 2, skip any characters in the string that are in the Unicode character class Zs (this might match zero characters). [UNICODE]
  6. If there are still further characters in the string, and the next character in the string is a valid denominator punctuation character, set denominator to that character.
  7. If the string contains any other characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, but denominator was given a value in the step 6, return nothing and abort these steps.
  8. Otherwise, if denominator was given a value in step 6, return number1 and denominator and abort these steps.
  9. Find a number in the string again, starting immediately after the last character that was examined by the sub-algorithm in step 2.
  10. If the sub-algorithm in step 9 returned nothing or an error condition, return nothing and abort these steps.
  11. Set number2 to the number returned by the sub-algorithm in step 9.
  12. If there are still further characters in the string, and the next character in the string is a valid denominator punctuation character, return nothing and abort these steps.
  13. If the string contains any other characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, return nothing and abort these steps.
  14. Otherwise, return number1 and number2.

The algorithm to find a number is as follows. It is given a string and a starting position, and returns either nothing, a number, or an error condition.

  1. Starting at the given starting position, ignore all characters in the given string until the first character that is either a U+002E FULL STOP or one of the ten characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE.
  2. If there are no such characters, return nothing and abort these steps.
  3. Starting with the character matched in step 1, collect all the consecutive characters that are either a U+002E FULL STOP or one of the ten characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, and assign this string of one or more characters to string.
  4. If string contains more than one U+002E FULL STOP character then return an error condition and abort these steps.
  5. Parse string according to the rules for parsing floating point number values, to obtain number. This step cannot fail (string is guarenteed to be a valid floating point number).
  6. Return number.
3.2.3.5. Percentages and dimensions

valid non-negative percentages, rules for parsing dimension values (only used by height/width on img, embed, object — maybe they should do the same as canvas, then this wouldn't even be needed)

3.2.3.6. Lists of integers

A valid list of integers is a number of valid integers separated by U+002C COMMA characters, with no other characters (e.g. no space characters). In addition, there might be restrictions on the number of integers that can be given, or on the range of values allowed.

The rules for parsing a list of integers are as follows:

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let numbers be an initially empty list of integers. This list will be the result of this algorithm.

  4. If there is a character in the string input at position position, and it is either U+002C COMMA character or a U+0020 SPACE character, then advance position to the next character in input, or to beyond the end of the string if there are no more characters.

  5. If position points to beyond the end of input, return numbers and abort.

  6. If the character in the string input at position position is a U+002C COMMA character or a U+0020 SPACE character, return to step 4.

  7. Let negated be false.

  8. Let value be 0.

  9. Let multiple be 1.

  10. Let started be false.

  11. Let finished be false.

  12. Let bogus be false.

  13. Parser: If the character in the string input at position position is:

    A U+002D HYPHEN-MINUS character

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. If started is true or if bogus is true, let negated be false.
    3. Otherwise, if started is false and if bogus is false, let negated be true.
    4. Let started be true.
    A character in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. Let n be the value of the digit, interpreted in base ten, multiplied by multiple.
    3. Add n to value.
    4. If value is greater than zero, multiply multiple by ten.
    5. Let started be true.
    A U+002C COMMA character
    A U+0020 SPACE character

    Follow these substeps:

    1. If started is false, return the numbers list and abort.
    2. If negated is true, then negate value.
    3. Append value to the numbers list.
    4. Jump to step 4 in the overall set of steps.
    A U+002E FULL STOP character

    Follow these substeps:

    1. Let finished be true.
    Any other character

    Follow these substeps:

    1. If finished is true, skip to the next step in the overall set of steps.
    2. Let negated be false.
    3. Let bogus be true.
    4. If started is true, then return the numbers list, and abort. (The value in value is not appended to the list first; it is dropped.)
  14. Advance position to the next character in input, or to beyond the end of the string if there are no more characters.

  15. If position points to a character (and not to beyond the end of input), jump to the big Parser step above.

  16. If negated is true, then negate value.

  17. If started is true, then append value to the numbers list, return that list, and abort.

  18. Return the numbers list and abort.

3.2.4. Dates and times

In the algorithms below, the number of days in month month of year year is: 31 if month is 1, 3, 5, 7, 8, 10, or 12; 30 if month is 4, 6, 9, or 11; 29 if month is 2 and year is a number divisible by 400, or if year is a number divisible by 4 but not by 100; and 28 otherwise. This takes into account leap years in the Gregorian calendar. [GREGORIAN]

3.2.4.1. Specific moments in time

A string is a valid datetime if it has four digits (representing the year), a literal hyphen, two digits (representing the month), a literal hyphen, two digits (representing the day), optionally some spaces, either a literal T or a space, optionally some more spaces, two digits (for the hour), a colon, two digits (the minutes), optionally the seconds (which, if included, must consist of another colon, two digits (the integer part of the seconds), and optionally a decimal point followed by one or more digits (for the fractional part of the seconds)), optionally some spaces, and finally either a literal Z (indicating the time zone is UTC), or, a plus sign or a minus sign followed by two digits, a colon, and two digits (for the sign, the hours and minutes of the timezone offset respectively); with the month-day combination being a valid date in the given year according to the Gregorian calendar, the hour values (h) being in the range 0 ≤ h ≤ 23, the minute values (m) in the range 0 ≤ m ≤ 59, and the second value (s) being in the range 0 ≤ h < 60. [GREGORIAN]

The digits must be characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), the hyphens must be a U+002D HYPHEN-MINUS characters, the T must be a U+0054 LATIN CAPITAL LETTER T, the colons must be U+003A COLON characters, the decimal point must be a U+002E FULL STOP, the Z must be a U+005A LATIN CAPITAL LETTER Z, the plus sign must be a U+002B PLUS SIGN, and the minus U+002D (same as the hyphen).

The following are some examples of dates written as valid datetimes.

"0037-12-13 00:00 Z"
Midnight UTC on the birthday of Nero (the Roman Emperor).
"1979-10-14T12:00:00.001-04:00"
One millisecond after noon on October 14th 1979, in the time zone in use on the east coast of North America during daylight saving time.
"8592-01-01 T 02:09 +02:09"
Midnight UTC on the 1st of January, 8592. The time zone associated with that time is two hours and nine minutes ahead of UTC.

Several things are notable about these dates:

Conformance checkers can use the algorithm below to determine if a datetime is a valid datetime or not.

To parse a string as a datetime value, a user agent must apply the following algorithm to the string. This will either return a time in UTC, with associated timezone information for round tripping or display purposes, or nothing, indicating the value is not a valid datetime. If at any point the algorithm says that it "fails", this means that it returns nothing.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly four characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the year.

  4. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

  5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the month.

  6. If month is not a number in the range 1 ≤ month ≤ 12, then fail.
  7. Let maxday be the number of days in month month of year year.

  8. If position is beyond the end of input or if the character at position is not a U+002D HYPHEN-MINUS character, then fail. Otherwise, move position forwards one character.

  9. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the day.

  10. If day is not a number in the range 1 ≤ month ≤ maxday, then fail.

  11. Collect a sequence of characters that are either U+0054 LATIN CAPITAL LETTER T characters or space characters. If the collected sequence is zero characters long, or if it contains more than one U+0054 LATIN CAPITAL LETTER T character, then fail.

  12. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the hour.

  13. If hour is not a number in the range 0 ≤ hour ≤ 23, then fail.
  14. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.

  15. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the minute.

  16. If minute is not a number in the range 0 ≤ minute ≤ 59, then fail.
  17. Let second be a string with the value "0".

  18. If position is beyond the end of input, then fail.

  19. If the character at position is a U+003A COLON, then:

    1. Advance position to the next character in input.

    2. If position is beyond the end of input, or at the last character in input, or if the next two characters in input starting at position are not two characters both in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then fail.

    3. Collect a sequence of characters that are either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) or U+002E FULL STOP characters. If the collected sequence has more than one U+002E FULL STOP characters, or if the last character in the sequence is a U+002E FULL STOP character, then fail. Otherwise, let the collected string be second instead of its previous value.

  20. Interpret second as a base ten number (possibly with a fractional part). Let that number be second instead of the string version.

  21. If second is not a number in the range 0 ≤ hour < 60, then fail. (The values 60 and 61 are not allowed: leap seconds cannot be represented by datetime values.)
  22. If position is beyond the end of input, then fail.

  23. Skip whitespace.

  24. If the character at position is a U+005A LATIN CAPITAL LETTER Z, then:

    1. Let timezonehours be 0.

    2. Let timezoneminutes be 0.

    3. Advance position to the next character in input.

  25. Otherwise, if the character at position is either a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:

    1. If the character at position is a U+002B PLUS SIGN ("+"), let sign be "positive". Otherwise, it's a U+002D HYPHEN-MINUS ("-"); let sign be "negative".

    2. Advance position to the next character in input.

    3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the timezonehours.

    4. If timezonehours is not a number in the range 0 ≤ timezonehours ≤ 23, then fail.
    5. If sign is "negative", then negate timezonehours.
    6. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then fail. Otherwise, move position forwards one character.

    7. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then fail. Otherwise, interpret the resulting sequence as a base ten integer. Let that number be the timezoneminutes.

    8. If timezoneminutes is not a number in the range 0 ≤ timezoneminutes ≤ 59, then fail.
    9. If sign is "negative", then negate timezoneminutes.
  26. If position is not beyond the end of input, then fail.

  27. Let time be the moment in time at year year, month month, day day, hours hour, minute minute, second second, subtracting timezonehours hours and timezoneminutes minutes. That moment in time is a moment in the UTC timezone.

  28. Let timezone be timezonehours hours and timezoneminutes minutes from UTC.

  29. Return time and timezone.

3.2.4.2. Vaguer moments in time

This section defines date or time strings. There are two kinds, date or time strings in content, and date or time strings in attributes. The only difference is in the handling of whitespace characters.

To parse a date or time string, user agents must use the following algorithm. A date or time string is a valid date or time string if the following algorithm, when run on the string, doesn't say the string is invalid.

The algorithm may return nothing (in which case the string will be invalid), or it may return a date, a time, a date and a time, or a date and a time and and a timezone. Even if the algorithm returns one or more values, the string can still be invalid.

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let results be the collection of results that are to be returned (one or more of a date, a time, and a timezone), initially empty. If the algorithm aborts at any point, then whatever is currently in results must be returned as the result of the algorithm.

  4. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

  5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

  6. Let the sequence of characters collected in the last step be s.

  7. If position is past the end of input, the string is invalid; abort these steps.

  8. If the character at position is not a U+003A COLON character, then:

    1. If the character at position is not a U+002D HYPHEN-MINUS ("-") character either, then the string is invalid, abort these steps.

    2. If the sequence s is not exactly four digits long, then the string is invalid. (This does not stop the algorithm, however.)

    3. Interpret the sequence of characters collected in step 5 as a base ten integer, and let that number be year.

    4. Advance position past the U+002D HYPHEN-MINUS ("-") character.

    5. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

    6. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

    7. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be month.

    8. If month is not a number in the range 1 ≤ month ≤ 12, then the string is invalid, abort these steps.
    9. Let maxday be the number of days in month month of year year.

    10. If position is past the end of input, or if the character at position is not a U+002D HYPHEN-MINUS ("-") character, then the string is invalid, abort these steps. Otherwise, advance position to the next character.

    11. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

    12. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

    13. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be day.

    14. If day is not a number in the range 1 ≤ day ≤ maxday, then the string is invalid, abort these steps.

    15. Add the date represented by year, month, and day to the results.

    16. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

    17. If the character at position is a U+0054 LATIN CAPITAL LETTER T, then move position forwards one character.

    18. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

    19. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

    20. Let s be the sequence of characters collected in the last step.

  9. If s is not exactly two digits long, then the string is invalid.

  10. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be hour.

  11. If hour is not a number in the range 0 ≤ hour ≤ 23, then the string is invalid, abort these steps.

  12. If position is past the end of input, or if the character at position is not a U+003A COLON character, then the string is invalid, abort these steps. Otherwise, advance position to the next character.

  13. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is empty, then the string is invalid; abort these steps.

  14. If the sequence collected in the last step is not exactly two digits long, then the string is invalid.

  15. Interpret the sequence of characters collected two steps ago as a base ten integer, and let that number be minute.

  16. If minute is not a number in the range 0 ≤ minute ≤ 59, then the string is invalid, abort these steps.

  17. Let second be 0. It may be changed to another value in the next step.

  18. If position is not past the end of input and the character at position is a U+003A COLON character, then:

    1. Collect a sequence of characters that are either characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9) or are U+002E FULL STOP. If the collected sequence is empty, or contains more than one U+002E FULL STOP character, then the string is invalid; abort these steps.

    2. If the first character in the sequence collected in the last step is not in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9), then the string is invalid.

    3. Interpret the sequence of characters collected two steps ago as a base ten number (possibly with a fractional part), and let that number be second.

    4. If second is not a number in the range 0 ≤ minute < 60, then the string is invalid, abort these steps.

  19. Add the time represented by hour, minute, and second to the results.

  20. If results has both a date and a time, then:

    1. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

    2. If position is past the end of input, then skip to the next step in the overall set of steps.

    3. Otherwise, if the character at position is a U+005A LATIN CAPITAL LETTER Z, then:

      1. Add the timezone corresponding to UTC (zero offset) to the results.

      2. Advance position to the next character in input.

      3. Skip to the next step in the overall set of steps.

    4. Otherwise, if the character at position is either a U+002B PLUS SIGN ("+") or a U+002D HYPHEN-MINUS ("-"), then:

      1. If the character at position is a U+002B PLUS SIGN ("+"), let sign be "positive". Otherwise, it's a U+002D HYPHEN-MINUS ("-"); let sign be "negative".

      2. Advance position to the next character in input.

      3. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then the string is invalid.

      4. Interpret the sequence collected in the last step as a base ten number, and let that number be timezonehours.

      5. If timezonehours is not a number in the range 0 ≤ timezonehours ≤ 23, then the string is invalid; abort these steps.
      6. If sign is "negative", then negate timezonehours.
      7. If position is beyond the end of input or if the character at position is not a U+003A COLON character, then the string is invalid; abort these steps. Otherwise, move position forwards one character.

      8. Collect a sequence of characters in the range U+0030 DIGIT ZERO (0) to U+0039 DIGIT NINE (9). If the collected sequence is not exactly two characters long, then the string is invalid.

      9. Interpret the sequence collected in the last step as a base ten number, and let that number be timezoneminutes.

      10. If timezoneminutes is not a number in the range 0 ≤ timezoneminutes ≤ 59, then the string is invalid; abort these steps.
      11. Add the timezone corresponding to an offset of timezonehours hours and timezoneminutes minutes to the results.

      12. Skip to the next step in the overall set of steps.

    5. Otherwise, the string is invalid; abort these steps.

  21. For the "in content" variant: skip Zs characters; for the "in attributes" variant: skip whitespace.

  22. If position is not past the end of input, then the string is invalid.

  23. Abort these steps (the string is parsed).

3.2.5. Time offsets

valid time offset, rules for parsing time offsets, time offset serialisation rules; in the format "5d4h3m2s1ms" or "3m 9.2s" or "00:00:00.00" or similar.

3.2.6. Tokens

A set of space-separated tokens is a set of zero or more words separated by one or more space characters, where words consist of any string of one or more characters, none of which are space characters.

A string containing a set of space-separated tokens may have leading or trailing space characters.

An unordered set of space-separated tokens is a set of space-separated tokens where none of the words are duplicated.

An ordered set of unique space-separated tokens is a set of space-separated tokens where none of the words are duplicated but where the order of the tokens is meaningful.

When a user agent has to split a string on spaces, it must use the following algorithm:

  1. Let input be the string being parsed.

  2. Let position be a pointer into input, initially pointing at the start of the string.

  3. Let tokens be a list of tokens, initially empty.

  4. Skip whitespace

  5. While position is not past the end of input:

    1. Collect a sequence of characters that are not space characters.

    2. Add the string collected in the previous step to tokens.

    3. Skip whitespace

  6. Return tokens.

When a user agent has to remove a token from a string, it must use the following algorithm:

  1. Let input be the string being modified.

  2. Let token be the token being removed. It will not contain any space characters.

  3. Let output be the output string, initially empty.

  4. Let position be a pointer into input, initially pointing at the start of the string.

  5. If position is beyond the end of input, set the string being modified to output, and abort these steps.

  6. If the character at position is a space character:

    1. Append the character at position to the end of output.

    2. Increment position so it points at the next character in input.

    3. Return to step 5 in the overall set of steps.

  7. Otherwise, the character at position is the first character of a token. Collect a sequence of characters that are not space characters, and let that be s.

  8. If s is exactly equal to token, then:

    1. Skip whitespace (in input).

    2. Remove any space characters currently at the end of output.

    3. If position is not past the end of input, and output is not the empty string, append a single U+0020 SPACE character at the end of output.

  9. Otherwise, append s to the end of output.

  10. Return to step 6 in the overall set of steps.

This causes any occurrences of the token to be removed from the string, and any spaces that were surrounding the token to be collapsed to a single space, except at the start and end of the string, where such spaces are removed.

3.2.7. Keywords and enumerated attributes

Some attributes are defined as taking one of a finite set of keywords. Such attributes are called enumerated attributes. The keywords are each defined to map to a particular state (several keywords might map to the same state, in which case some of the keywords are synonyms of each other; additionally, some of the keywords can be said to be non-conforming, and are only in the specification for historical reasons). In addition, two default states can be given. The first is the invalid value default, the second is the missing value default.

If an enumerated attribute is specified, the attribute's value must be one of the given keywords that are not said to be non-conforming, with no leading or trailing whitespace. The keyword may use any mix of uppercase and lowercase letters.

When the attribute is specified, if its value case-insensitively matches one of the given keywords then that keyword's state is the state that the attribute represents. If the attribute value matches none of the given keywords, but the attribute has an invalid value default, then the attribute represents that state. Otherwise, if the attribute value matches none of the keywords but there is a missing value default state defined, then that is the state represented by the attribute. Otherwise, there is no default, and invalid values must simply be ignored.

When the attribute is not specified, if there is a missing value default state defined, then that is the state represented by the (missing) attribute. Otherwise, the absence of the attribute means that there is no state represented.

The empty string can be one of the keywords in some cases. For example the contenteditable attribute has two states: true, matching the true keyword and the empty string, false, matching false and all other keywords (it's the invalid value default). It could further be thought of as having a third state inherit, which would be the default when the attribute is not specified at all (the missing value default), but for various reasons that isn't the way this specification actually defines it.

3.2.8. References

A valid hashed ID reference to an element of type type is a string consisting of a U+0023 NUMBER SIGN (#) character followed by a string which exactly matches the value of the id attribute of an element in the document with type type.

The rules for parsing a hashed ID reference to an element of type type are as follows:

  1. If the string being parsed does not contain a U+0023 NUMBER SIGN character, or if the first such character in the string is the last character in the string, then return null and abort these steps.

  2. Let s be the string from the character immediately after the first U+0023 NUMBER SIGN character in the string being parsed up to the end of that string.

  3. Return the first element of type type that has an id or name attribute whose value case-insensitively matches s.

3.3. Documents and document fragments

3.3.1. Semantics

Elements, attributes, and attribute values in HTML are defined (by this specification) to have certain meanings (semantics). For example, the ol element represents an ordered list, and the lang attribute represents the language of the content.

Authors must only use elements, attributes, and attribute values for their appropriate semantic purposes.

For example, the following document is non-conforming, despite being syntactically correct:

<!DOCTYPE html>
<html lang="en-GB">
 <head> <title> Demonstration </title> </head>
 <body>
  <table>
   <tr> <td> My favourite animal is the cat. </td> </tr>
   <tr>
    <td>
     —<a href="http://example.org/~ernest/"><cite>Ernest</cite></a>,
     in an essay from 1992
    </td>
   </tr>
  </table>
 </body>
</html>

...because the data placed in the cells is clearly not tabular data. A corrected version of this document might be:

<!DOCTYPE html>
<html lang="en-GB">
 <head> <title> Demonstration </title> </head>
 <body>
  <blockquote>
   <p> My favourite animal is the cat. </p>
  </blockquote>
  <p>
   —<a href="http://example.org/~ernest/"><cite>Ernest</cite></a>,
   in an essay from 1992
  </p>
 </body>
</html>

This next document fragment, intended to represent the heading of a corporate site, is similarly non-conforming because the second line is not intended to be a heading of a subsection, but merely a subheading or subtitle (a subordinate heading for the same section).

<body>
 <h1>ABC Company</h1>
 <h2>Leading the way in widget design since 1432</h2>
 ...

The header element should be used in these kinds of situations:

<body>
 <header>
  <h1>ABC Company</h1>
  <h2>Leading the way in widget design since 1432</h2>
 </header>
 ...

Through scripting and using other mechanisms, the values of attributes, text, and indeed the entire structure of the document may change dynamically while a user agent is processing it. The semantics of a document at an instant in time are those represented by the state of the document at that instant in time, and the semantics of a document can therefore change over time. User agents must update their presentation of the document as this occurs.

HTML has a progress element that describes a progress bar. If its "value" attribute is dynamically updated by a script, the UA would update the rendering to show the progress changing.

3.3.2. Structure

All the elements in this specification have a defined content model, which describes what nodes are allowed inside the elements, and thus what the structure of an HTML document or fragment must look like. Authors must only put elements inside an element if that element allows them to be there according to its content model.

As noted in the conformance and terminology sections, for the purposes of determining if an element matches its content model or not, CDATASection nodes in the DOM are treated as equivalent to Text nodes, and entity reference nodes are treated as if they were expanded in place.

The space characters are always allowed between elements. User agents represent these characters between elements in the source markup as text nodes in the DOM. Empty text nodes and text nodes consisting of just sequences of those characters are considered inter-element whitespace.

Inter-element whitespace, comment nodes, and processing instruction nodes must be ignored when establishing whether an element matches its content model or not, and must be ignored when following algorithms that define document and element semantics.

An element A is said to be preceeded or followed by a second element B if A and B have the same parent node and there are no other element nodes or text nodes (other than inter-element whitespace) between them.

Authors must only use elements in the HTML namespace in the contexts where they are allowed, as defined for each element. For XML compound documents, these contexts could be inside elements from other namespaces, if those elements are defined as providing the relevant contexts.

The SVG specification defines the SVG foreignObject element as allowing foreign namespaces to be included, thus allowing compound documents to be created by inserting subdocument content under that element. This specification defines the XHTML html element as being allowed where subdocument fragments are allowed in a compound document. Together, these two definitions mean that placing an XHTML html element as a child of an SVG foreignObject element is conforming.

3.3.3. Kinds of elements

Each element in HTML falls into zero or more categories that group elements with similar characteristics together. This specification uses the following categories:

Some elements have unique requirements and do not fit into any particular category.

In addition, some elements represent various common concepts; for example, some elements represent paragraphs.

3.3.3.1. Block-level elements

Block-level elements are used for structural grouping of page content.

There are several kinds of block-level elements:

There are also elements that seem to be block-level but aren't, such as body, li, dt, dd, and td. These elements are allowed only in specific places, not simply anywhere that block-level elements are allowed.

Some block-level elements play multiple roles. For instance, the script elements is allowed inside head elements and can also be used as inline-level content. Similarly, the ul, ol, dl, table, and blockquote elements play dual roles as both block-level and inline-level elements.

3.3.3.2. Inline-level content

Inline-level content consists of text and various elements to annotate the text, as well as some embedded content (such as images or sound clips).

Inline-level content comes in various types:

Strictly inline-level content
Text, embedded content, and elements that annotate the text without introducing structural grouping. For example: a, meter, img. Elements used in contexts allowing only strictly inline-level content must not have any descendants that are anything other than strictly inline-level content.
Structured inline-level elements
Block-level elements that can also be used as inline-level content. For example: ol, blockquote, table.

Some elements are defined to have as a content model significant inline content. This means that at least one descendant of the element must be significant text or embedded content.

Unless an element's content model explicitly states that it must contain significant inline content, simply having no text nodes and no elements satisfies an element whose content model is some kind of inline content.

Significant text, for the purposes of determining the presence of significant inline content, consists of any character other than those falling in the Unicode categories Zs, Zl, Zp, Cc, and Cf. [UNICODE]

The following three paragraphs are non-conforming because their content model is not satisfied (they all count as empty).

<p></p>
<p><em>&#x00A0;</em></p>
<p>
 <ol>
  <li></li>
 </ol>
</p>

Embedded content consists of elements that introduce content from other resources into the document, for example img. Embedded content elements can have fallback content: content that is to be used when the external resource cannot be used (e.g. because it is of an unsupported format). The element definitions state what the fallback is, if any.

3.3.3.3. Transparent content models

Some elements are described as transparent; they have "transparent" as their content model. Some elements are described as semi-transparent; this means that part of their content model is "transparent" but that is not the only part of the content model that must be satisfied.

When a content model includes a part that is "transparent", those parts must only contain content that would still be conformant if all transparent and semi-transparent elements in the tree were replaced, in their parent element, by the children in the "transparent" part of their content model, retaining order.

When a transparent or semi-transparent element has no parent, then the part of its content model that is "transparent" must instead be treated as zero or more block-level elements, or inline-level content (but not both).

3.3.3.4. Determining if a particular element contains block-level elements or inline-level content

Some elements are defined to have content models that allow either block-level elements or inline-level content, but not both. For example, the aside and li elements.

To establish whether such an element is being used as a block-level container or as an inline-level container, for example in order to determine if a document conforms to these requirements, user agents must look at the element's child nodes. If any of the child nodes are not allowed in block-level contexts, then the element is being used for inline-level content. If all the child nodes are allowed in a block-level context, then the element is being used for block-level elements.

Whenever this search would examine a transparent element, the element's own child nodes must be examined instead, potentially recursing further if any of those are themselves transparent.

For instance, in the following (non-conforming) XML fragment, the li element is being used as an inline-level element container, because the meta element is not allowed in a block-level context. (It doesn't matter, for the purposes of determining whether it is an inline-level or block-level context, that the meta element is not allowed in inline-level contexts either.)

<ol>
 <li>
  <p> Hello World </p>
  <meta title="this is an invalid example"/>
 </li>
</ol>

In the following fragment, the aside element is being used as a block-level container, because even though all the elements it contains could be considered inline-level elements, there are no nodes that can only be considered inline-level.

<aside>
 <ol>
  <li> ... </li>
 </ol>
 <ul>
  <li> ... </li>
 </ul>
</aside>

On the other hand, in the following similar fragment, the aside element is an inline-level container, because the text ("Foo") can only be considered inline-level.

<aside>
 <ol>
  <li> ... </li>
 </ol>
 Foo
</aside>
3.3.3.5. Interactive elements

Parts of this section should eventually be moved to DOM3 Events.

Certain elements in HTML can be activated, for instance a elements, button elements, or input elements when their type attribute is set to radio. Activation of those elements can happen in various (UA-defined) ways, for instance via the mouse or keyboard.

When activation is performed via some method other than clicking the pointing device, the default action of the event that triggers the activation must, instead of being activating the element directly, be to fire a click event on the same element.

The default action of this click event, or of the real click event if the element was activated by clicking a pointing device, must be to fire a further DOMActivate event at the same element, whose own default action is to go through all the elements the DOMActivate event bubbled through (starting at the target node and going towards the Document node), looking for an element with an activation behavior; the first element, in reverse tree order, to have one, must have its activation behavior executed.

The above doesn't happen for arbitrary synthetic events dispatched by author script. However, the click() method can be used to make it happen programmatically.

For certain form controls, this process is complicated further by changes that must happen around the click event. [WF2]

Most interactive elements have content models that disallow nesting interactive elements.

3.3.3.6. Paragraphs

A paragraph is typically a block of text with one or more sentences that discuss a particular topic, as in typography, but can also be used for more general thematic grouping. For instance, an address is also a paragraph, as is a part of a form, a byline, or a stanza in a poem.

Paragraphs can be represented by several elements. The address element always represents a paragraph of contact information for its section, the aside, nav, footer, li, and dd elements represent paragraphs with various specific semantics when they are used as inline-level content containers, the figure element represents a paragraph in the form of embedded content, and the p element represents all the other kinds of paragraphs, for which there are no dedicated elements.

3.4. Global attributes

The following attributes are common to and may be specified on all HTML elements (even those not defined in this specification):

Global attributes:
class
contenteditable
contextmenu
dir
draggable
id
irrelevant
lang
tabindex
title

In addition, the following event handler content attributes may be specified on any HTML element:

3.4.1. The id attribute

The id attribute represents its element's unique identifier. The value must be unique in the subtree within which the element finds itself and must contain at least one character. The value must not contain any space characters.

If the value is not the empty string, user agents must associate the element with the given value (exactly, including any space characters) for the purposes of ID matching within the subtree the element finds itself (e.g. for selectors in CSS or for the getElementById() method in the DOM).

Identifiers are opaque strings. Particular meanings should not be derived from the value of the id attribute.

This specification doesn't preclude an element having multiple IDs, if other mechanisms (e.g. DOM Core methods) can set an element's ID in a way that doesn't conflict with the id attribute.

The id DOM attribute must reflect the id content attribute.

3.4.2. The title attribute

The title attribute represents advisory information for the element, such as would be appropriate for a tooltip. On a link, this could be the title or a description of the target resource; on an image, it could be the image credit or a description of the image; on a paragraph, it could be a footnote or commentary on the text; on a citation, it could be further information about the source; and so forth. The value is text.

If this attribute is omitted from an element, then it implies that the title attribute of the nearest ancestor with a title attribute set is also relevant to this element. Setting the attribute overrides this, explicitly stating that the advisory information of any ancestors is not relevant to this element. Setting the attribute to the empty string indicates that the element has no advisory information.

If the title attribute's value contains U+000A LINE FEED (LF) characters, the content is split into multiple lines. Each U+000A LINE FEED (LF) character represents a line break.

Some elements, such as link and dfn, define additional semantics for the title attribute beyond the semantics described above.

The title DOM attribute must reflect the title content attribute.

3.4.3. The lang (HTML only) and xml:lang (XML only) attributes

The lang attribute specifies the primary language for the element's contents and for any of the element's attributes that contain text. Its value must be a valid RFC 3066 language code, or the empty string. [RFC3066]

The xml:lang attribute is defined in XML. [XML]

If these attributes are omitted from an element, then it implies that the language of this element is the same as the language of the parent element. Setting the attribute to the empty string indicates that the primary language is unknown.

The lang attribute may only be used on elements of HTML documents. Authors must not use the lang attribute in XML documents.

The xml:lang attribute may only be used on elements of XML documents. Authors must not use the xml:lang attribute in HTML documents.

To determine the language of a node, user agents must look at the nearest ancestor element (including the element itself if the node is an element) that has a lang or xml:lang attribute set. That specifies the language of the node.

If both the xml:lang attribute and the lang attribute are set on an element, user agents must use the xml:lang attribute, and the lang attribute must be ignored for the purposes of determining the element's language.

If no explicit language is given for the root element, then language information from a higher-level protocol (such as HTTP), if any, must be used as the final fallback language. In the absence of any language information, the default value is unknown (the empty string).

User agents may use the element's language to determine proper processing or rendering (e.g. in the selection of appropriate fonts or pronounciations, or for dictionary selection).

The lang DOM attribute must reflect the lang content attribute.

3.4.4. The dir attribute

The dir attribute specifies the element's text directionality. The attribute is an enumerated attribute with the keyword ltr mapping to the state ltr, and the keyword rtl mapping to the state rtl. The attribute has no defaults.

If the attribute has the state ltr, the element's directionality is left-to-right. If the attribute has the state rtl, the element's directionality is right-to-left. Otherwise, the element's directionality is the same as its parent.

The processing of this attribute depends on the presentation layer. For example, CSS 2.1 defines a mapping from this attribute to the CSS 'direction' and 'unicode-bidi' properties, and defines rendering in terms of those properties.

The dir DOM attribute on an element must reflect the dir content attribute of that element, limited to only known values.

The dir DOM attribute on HTMLDocument objects must reflect the dir content attribute of the html element, if any, limited to only known values. If there is no such element, then the attribute must return the empty string and do nothing on setting.

3.4.5. The class attribute

Every HTML element may have a class attribute specified.

The attribute, if specified, must have a value that is an unordered set of space-separated tokens representing the various classes that the element belongs to.

The classes that an HTML element has assigned to it consists of all the classes returned when the value of the class attribute is split on spaces.

Assigning classes to an element affects class matching in selectors in CSS, the getElementsByClassName() method in the DOM, and other such features.

Authors may use any value in the class attribute, but are encouraged to use the values that describe the nature of the content, rather than values that describe the desired presentation of the content.

The className and classList DOM attributes must both reflect the class content attribute.

3.4.6. The irrelevant attribute

All elements may have the irrelevant content attribute set. The irrelevant attribute is a boolean attribute. When specified on an element, it indicates that the element is not yet, or is no longer, relevant. User agents should not render elements that have the irrelevant attribute specified.

In the following skeletal example, the attribute is used to hide the a Web game until the user logs in:

  <h1>The Example Game</h1>
  <section id="login">
   <h2>Login</h2>
   <form>
    ...
    <!-- calls login() once the user's credentials have been checked -->
   </form>
   <script>
    function login() {
      // switch screens
      document.getElementById('login').irrelevant = true;
      document.getElementById('game').irrelevant = false;
    }
   </script>
  </section>
  <section id="game">
   ...
  </section>

In the following example, an image acts as a surrogate for an video. When the image is clicked, it tries to load the video (and disables the playback button). If the load succeeds enough that a frame of data has been downloaded, the video element hides the surrogate image and shows the video instead, along with its controls, and turns on autoplay (so that the video will commence playback as soon as enough of it is loaded). If the load fails for any reason, the video and the surrogate frame are both hidden (by hiding the paragraph element containing them both), and the following paragraph is shown instead, with its unhelpful error message and potentially helpful link to download the video directly.

In legacy user agents, the surrogate image would show (though clicking it would have no effect) and the link to the video would be present (allowing the video to be viewed in another application).

  <p>
   <input type="image" src="frame.png" alt="Play Video"
     onclick="   nextSibling.load();
                 disabled = true;
                 return false;"
   ><video src="video.ogg" controls="" irrelevant=""
     onloadedfirstframe="
                 irrelevant = false;
                 previousSibling.irrelevant = true;
                 autoplay = true"
     onerror="   parentNode.irrelevant = true;
                 parentNode.nextSibling.irrelevant = false">
   </video>
  </p><p irrelevant="">
   Playback unavailable.
   <a href="video.ogg">Download Video</a>
  </p>

The irrelevant attribute must not be used to hide content that could legitimately be shown in another presentation. For example, it is incorrect to use irrelevant to hide panels in a tabbed dialog, because the tabbed interface is merely a kind of overflow presentation — showing all the form controls in one big page with a scrollbar would be equivalent, and no less correct.

Elements in a section hidden by the irrelevant attribute are still active, e.g. scripts and form controls in such sections still render execute and submit respectively. Only their presentation to the user changes.

The irrelevant DOM attribute must reflect the content attribute of the same name.

3.5. Interaction

3.5.1. Activation

The click() method must fire a click event at the element, whose default action is the firing of a further DOMActivate event at the same element, whose own default action is to go through all the elements the DOMActivate event bubbled through (starting at the target node and going towards the Document node), looking for an element with an activation behavior; the first element, in reverse tree order, to have one, must have its activation behavior executed.

3.5.2. Focus

When an element is focused, key events received by the document must be targeted at that element. There is always an element focused; in the absence of other elements being focused, the document's root element is it.

Which element within a document currently has focus is independent of whether or not the document itself has the system focus.

Some focusable elements might take part in sequential focus navigation.

3.5.2.1. Focus management

The focus() and blur() methods must focus and unfocus the element respectively, if the element is focusable.

Some elements, most notably area, can correspond to more than one distinct focusable area. When such an element is focused using the focus() method, the first such region in tree order is the one that must be focused.

Well that clearly needs more.

The activeElement attribute must return the element in the document that has focus. If no element specifically has focus, this must return the body element.

The hasFocus attribute must return true if the document, one of its nested browsing contexts, or any element in the document or its browsing contexts currently has the system focus.

3.5.2.2. Sequential focus navigation

This section on the tabindex attribute needs to be checked for backwards-compatibility.

The tabindex attribute specifies the relative order of elements for the purposes of sequential focus navigation. The name "tab index" comes from the common use of the "tab" key to navigate through the focusable elements. The term "tabbing" refers to moving forward through the focusable elements.

The tabindex attribute, if specified, must have a value that is a valid integer.

If the attribute is specified, it must be parsed using the rules for parsing integers. If parsing the value returns an error, the attribute is ignored for the purposes of focus management (as if it wasn't specified).

A positive integer or zero specifies the index of the element in the current scope's tab order. Elements with the same index are sorted in tree order for the purposes of tabbing.

A negative integer specifies that the element should be removed from the tab order. If the element does normally take focus, it may still be focused using other means (e.g. it could be focused by a click).

If the attribute is absent (or invalid), then the user agent must treat the element as if it had the value 0 or the value -1, based on platform conventions.

For example, a user agent might default textarea elements to 0, and button elements to -1, making text fields part of the tabbing cycle but buttons not.

When an element that does not normally take focus (i.e. whose default value would be -1) has the tabindex attribute specified with a positive value, then it should be added to the tab order and should be made focusable. When focused, the element matches the CSS :focus pseudo-class and key events are dispatched on that element in response to keyboard input.

The tabIndex DOM attribute reflects the value of the tabIndex content attribute. If the attribute is not present (or has an invalid value) then the DOM attribute must return the UA's default value for that element, which will be either 0 (for elements in the tab order) or -1 (for elements not in the tab order).

3.5.3. Scrolling elements into view

The scrollIntoView([top]) method, when called, must cause the element on which the method was called to have the attention of the user called to it.

In a speech browser, this could happen by having the current playback position move to the start of the given element.

In visual user agents, if the argument is present and has the value false, the user agent should scroll the element into view such that both the bottom and the top of the element are in the viewport, with the bottom of the element aligned with the bottom of the viewport. If it isn't possible to show the entire element in that way, or if the argument is omitted or is true, then the user agent must instead simply align the top of the element with the top of the viewport.

Non-visual user agents may ignore the argument, or may treat it in some media-specific manner most useful to the user.

3.6. The root element

3.6.1. The html element

Contexts in which this element may be used:
As the root element of a document.
Wherever a subdocument fragment is allowed in a compound document.
Content model:
A head element followed by a body element.
Element-specific attributes:
None (but see prose).
DOM interface:
No difference from HTMLElement.

The html element represents the root of an HTML document.

Though it has absolutely no effect and no meaning, the html element, in HTML documents, may have an xmlns attribute specified, if, and only if, it has the exact value "http://www.w3.org/1999/xhtml". This does not apply to XML documents.

In HTML, the xmlns attribute has absolutely no effect. It is basically a talisman. It is allowed merely to make migration to and from XHTML mildly easier. When parsed by an HTML parser, the attribute ends up in the null namespace, not the "http://www.w3.org/2000/xmlns/" namespace like namespace declaration attributes in XML do.

In XML, an xmlns attribute is part of the namespace declaration mechanism, and an element cannot actually have an xmlns attribute in the null namespace specified.

3.7. Document metadata

Document metadata is represented by metadata elements in the document's head element.

3.7.1. The head element

Contexts in which this element may be used:
As the first element in an html element.
Content model:
In any order unless otherwise specified: optionally one meta element with a charset attribute, exactly one title element, optionally one base element, and zero or more other metadata elements (in particular, link, meta, style, and script).
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The head element collects the document's metadata.

3.7.2. The title element

Metadata element.

Contexts in which this element may be used:
In a head element containing no other title elements.
Content model:
Text (for details, see prose).
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The title element represents the document's title or name. Authors should use titles that identify their documents even when they are used out of context, for example in a user's history or bookmarks, or in search results. The document's title is often different from its first header, since the first header does not have to stand alone when taken out of context.

Here are some examples of appropriate titles, contrasted with the top-level headers that might be used on those same pages.

  <title>Introduction to The Mating Rituals of Bees</title>
    ...
  <h1>Introduction</h1>
  <p>This companion guide to the highly successful
  <cite>Introduction to Medieval Bee-Keeping</cite> book is...

The next page might be a part of the same site. Note how the title describes the subject matter unambiguously, while the first header assumes the reader knowns what the context is and therefore won't wonder if the dances are Salsa or Waltz:

  <title>Dances used during bee mating rituals</title>
    ...
  <h1>The Dances</h1>

The title element must not contain any elements.

The string to use as the document's title is given by the document.title DOM attribute. User agents should use the document's title when referring to the document in their user interface.

3.7.3. The base element

Metadata element.

Contexts in which this element may be used:
In a head element, after the meta element with the charset attribute, if any, but before any other elements.
Content model:
Empty.
Element-specific attributes:
href
target
DOM interface:
interface HTMLBaseElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
};

The base element allows authors to specify the document's base URI for the purposes of resolving relative URIs, and the name of the default browsing context for the purposes of following hyperlinks.

There must be no more than one base element per document.

The href content attribute, if specified, must contain a URI (or IRI).

User agents must use the value of the href attribute of the first base element that is both a child of the head element and has an href attribute, if there is such an element, as the document entity's base URI for the purposes of section 5.1.1 of RFC 2396 ("Establishing a Base URI": "Base URI within Document Content"). This base URI from RFC 2396 is referred to by the algorithm given in XML Base, which is a normative part of this specification. [RFC2396]

If the base URI given by this attribute is a relative URI, it must be resolved relative to the higher-level base URIs (i.e. the base URI from the encapsulating entity or the URI used to retrieve the entity) to obtain an absolute base URI. All xml:base attributes must be ignored when resolving relative URIs in this href attribute.

If there are multiple base elements with href attributes, all but the first are ignored.

The target attribute, if specified, must contain a valid browsing context name. User agents use this name when following hyperlinks.

The href and target DOM attributes must reflect the content attributes of the same name.

Pages with multiple base elements have all but their first base element with an href attribute ignored for the purposes of URI resolution, and all but their first base element with a target attribute ignored for the purposes of default browsing context name resolution.

Metadata element.

Contexts in which this element may be used:
In a head element.
In a noscript element that is a child of a head element.
Content model:
Empty.
Element-specific attributes:
href (required)
rel (required)
media
hreflang
type
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLLinkElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString href;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
};

The LinkStyle interface must also be implemented by this element, the styling processing model defines how. [CSSOM]

The link element allows authors to indicate explicit relationships between their document and other resources.

The destination of the link is given by the href attribute, which must be present and must contain a URI (or IRI). If the href attribute is absent, then the element does not define a link.

The type of link indicated (the relationship) is given by the value of the rel attribute, which must be present, and must have a value that is an unordered set of space-separated tokens. The allowed values and their meanings are defined in a later section. If the rel attribute is absent, or if the value used is not allowed according to the definitions in this specification, then the element does not define a link.

Two categories of links can be created using the link element. Links to external resources are links to resources that are to be used to augment the current document, and hyperlink links are links to other documents. The link types section defines whether a particular link type is an external resource or a hyperlink. One element can create multiple links (of which some might be external resource links and some might be hyperlinks). User agents should process the links on a per-link basis, not a per-element basis.

The exact behaviour for links to external resources depends on the exact relationship, as defined for the relevant link type. Some of the attributes control whether or not the external resource is to be applied (as defined below). For external resources that are represented in the DOM (for example, style sheets), the DOM representation must be made available even if the resource is not applied. (However, user agents may opt to only fetch such resources when they are needed, instead of pro-actively downloading all the external resources that are not applied.)

Interactive user agents should provide users with a means to follow the hyperlinks created using the link element, somewhere within their user interface. The exact interface is not defined by this specification, but it should include the following information (obtained from the element's attributes, again as defined below), in some form or another (possibly simplified), for each hyperlink created with each link element in the document:

User agents may also include other information, such as the type of the resource (as given by the type attribute).

The media attribute says which media the resource applies to. The value must be a valid media query. [MQ]

If the link is a hyperlink then the media attribute is purely advisory, and describes for which media the document in question was designed.

However, if the link is an external resource link, then the media attribute is prescriptive. The user agent must only apply the external resource to views while their state match the listed media.

The default, if the media attribute is omitted, is all, meaning that by default links apply to all media.

The hreflang attribute on the link element has the same semantics as the hreflang attribute on hyperlink elements.

The type attribute gives the MIME type of the linked resource. It is purely advisory. The value must be a valid MIME type, optionally with parameters. [RFC2046]

For external resource links, user agents may use the type given in this attribute to decide whether or not to consider using the resource at all. If the UA does not support the given MIME type for the given link relationship, then the UA may opt not to download and apply the resource.

User agents must not consider the type attribute authoritative — upon fetching the resource, user agents must not use metadata included in the link to the resource to determine its type.

If the attribute is omitted, then the UA must fetch the resource to determine its type and thus determine if it supports (and can apply) that external resource.

If a document contains three style sheet links labelled as follows:

<link rel="stylesheet" href="A" type="text/css">
<link rel="stylesheet" href="B" type="text/plain">
<link rel="stylesheet" href="C">

...then a compliant UA that supported only CSS style sheets would fetch the A and C files, and skip the B file (since text/plain is not the MIME type for CSS style sheets). For these two files, it would then check the actual types returned by the UA. For those that are sent as text/css, it would apply the styles, but for those labelled as text/plain, or any other type, it would not.

The title attribute gives the title of the link. With one exception, it is purely advisory. The value is text. The exception is for style sheet links, where the title attribute defines alternative style sheet sets.

The title attribute on link elements differs from the global title attribute of most other elements in that a link without a title does not inherit the title of the parent element: it merely has no title.

Some versions of HTTP defined a Link: header, to be processed like a series of link elements. When processing links, those must be taken into consideration as well. For the purposes of ordering, links defined by HTTP headers must be assumed to come before any links in the document, in the order that they were given in the HTTP entity header. Relative URIs in these headers must be resolved according to the rules given in HTTP, not relative to base URIs set by the document (e.g. using a base element or xml:base attributes). [RFC2616] [RFC2068]

The DOM attributes href, rel, media, hreflang, and type each must reflect the respective content attributes of the same name.

The DOM attribute relList must reflect the rel content attribute.

The DOM attribute disabled only applies to style sheet links. When the link element defines a style sheet link, then the disabled attribute behaves as defined for the alternative style sheets DOM. For all other link elements it always return false and does nothing on setting.

3.7.5. The meta element

Metadata element.

Contexts in which this element may be used:
In a head element.
If the http-equiv attribute is present: in a noscript element that is a child of a head element.
Content model:
Empty.
Element-specific attributes:
name
http-equiv
content
charset (HTML only)
DOM interface:
interface HTMLMetaElement : HTMLElement {
           attribute DOMString content;
           attribute DOMString name;
           attribute DOMString httpEquiv;
};

The meta element represents various kinds of metadata that cannot be expressed using the title, base, link, style, and script elements.

The meta element can represent document-level metadata with the name attribute, pragma directives with the http-equiv attribute, and the file's character encoding declaration when an HTML document is serialised to string form (e.g. for transmission over the network or for disk storage) with the charset attribute.

Exactly one of the name, http-equiv, and charset attributes must be specified.

If either name or http-equiv is specified, then the content attribute must also be specified. Otherwise, it must be omitted.

The charset attribute may only be specified in HTML documents, it must not be used in XML documents. If the charset attribute is specified, the element must be the first element in the head element of the file.

The content attribute gives the value of the document metadata or pragma directive when the element is used for those purposes. The allowed values depend on the exact context, as described in subsequent sections of this specification.

If a meta element has a name attribute, it sets document metadata. Document metadata is expressed in terms of name/value pairs, the name attribute on the meta element giving the name, and the content attribute on the same element giving the value. The name specifies what aspect of metadata is being set; valid names and the meaning of their values are described in the following sections. If a meta element has no content attribute, then the value part of the metadata name/value pair is the empty string.

If a meta element has the http-equiv attribute specified, it must be either in a head element or in a noscript element that itself is in a head element. If a meta element does not have the http-equiv attribute specified, it must be in a head element.

The DOM attributes name and content must reflect the respective content attributes of the same name. The DOM attribute httpEquiv must reflect the content attribute http-equiv.

3.7.5.1. Standard metadata names

This specification defines a few names for the name attribute of the meta element.

generator

The value must be a free-form string that identifies the software used to generate the document. This value must not be used on hand-authored pages. WYSIWYG editors have additional constraints on the value used with this metadata name.

dns

The value must be an ordered set of unique space-separated tokens, each word of which is a host name. The list allows authors to provide a list of host names that the user is expected to subsequently need. User agents may, according to user preferences and prevailing network conditions, pre-emptively resolve the given DNS names (extracting the names from the value using the rules for splitting a string on spaces), thus precaching the DNS information for those hosts and potentially reducing the time between page loads for subsequent user interactions. Higher priority should be given to host names given earlier in the list.

3.7.5.2. Other metadata names

Extensions to the predefined set of metadata names may be registered in the WHATWG Wiki MetaExtensions page.

Anyone is free to edit the WHATWG Wiki MetaExtensions page at any time to add a type. These new names must be specified with the following information:

Keyword

The actual name being defined. The name should not be confusingly similar to any other defined name (e.g. differing only in case).

Brief description

A short description of what the metadata name's meaning is, including the format the value is required to be in.

Link to more details
A link to a more detailed description of the metadata name's semantics and requirements. It could be another page on the Wiki, or a link to an external page.
Synonyms

A list of other names that have exactly the same processing requirements. Authors should not use the names defined to be synonyms, they are only intended to allow user agents to support legacy content.

Status

One of the following:

Proposal
The name has not received wide peer review and approval. Someone has proposed it and is using it.
Accepted
The name has received wide peer review and approval. It has a specification that unambiguously defines how to handle pages that use the name, including when they use it in incorrect ways.
Unendorsed
The metadata name has received wide peer review and it has been found wanting. Existing pages are using this keyword, but new pages should avoid it. The "brief description" and "link to more details" entries will give details of what authors should use instead, if anything.

If a metadata name is added with the "proposal" status and found to be redundant with existing values, it should be removed and listed as a synonym for the existing value.

Conformance checkers must use the information given on the WHATWG Wiki MetaExtensions page to establish if a value not explicitly defined in this specification is allowed or not. When an author uses a new type not defined by either this specification or the Wiki page, conformance checkers should offer to add the value to the Wiki, with the details described above, with the "proposal" status.

This specification does not define how new values will get approved. It is expected that the Wiki will have a community that addresses this.

Metadata names whose values are to be URIs must not be proposed or accepted. Links must be represented using the link element, not the meta element.

3.7.5.3. Pragma directives

When the http-equiv attribute is specified on a meta element, the element is a pragma directive.

The http-equiv attribute is an enumerated attribute. The following table lists the keywords defined for this attribute. The states given in the first cell of the the rows with keywords give the states to which those keywords map.

State Keywords
Refresh refresh
Default style default-style

When a meta element is inserted into the document, if its http-equiv attribute is present and represents one of the above states, then the user agent must run the algorithm appropriate for that state, as described in the following list:

Refresh state
  1. If another meta element in the Refresh state has already been successfully processed (i.e. when it was inserted the user agent processed it and reached the last step of this list of steps), then abort these steps.

  2. If the meta element has no content attribute, or if that attribute's value is the empty string, then abort these steps.

  3. Let input be the value of the element's content attribute.

  4. Let position point at the first character of input.

  5. Skip whitespace.

  6. Collect a sequence of characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, and parse the resulting string using the rules for parsing non-negative integers. If the sequence of characters collected is the empty string, then no number will have been parsed; abort these steps. Otherwise, let time be the parsed number.

  7. Collect a sequence of characters in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE and U+002E FULL STOP ("."). Ignore any collected characters.

  8. Skip whitespace.

  9. Let url be the address of the current page.

  10. If the character in input pointed to by position is a U+003B SEMICOLON (";"), then advance position to the next character. Otherwise, jump to the last step.

  11. Skip whitespace.

  12. If the character in input pointed to by position is one of U+0055 LATIN CAPITAL LETTER U or U+0075 LATIN SMALL LETTER U, then advance position to the next character. Otherwise, jump to the last step.

  13. If the character in input pointed to by position is one of U+0052 LATIN CAPITAL LETTER R or U+0072 LATIN SMALL LETTER R, then advance position to the next character. Otherwise, jump to the last step.

  14. If the character in input pointed to by position is one of U+004C LATIN CAPITAL LETTER L or U+006C LATIN SMALL LETTER L, then advance position to the next character. Otherwise, jump to the last step.

  15. Skip whitespace.

  16. If the character in input pointed to by position is a U+003D EQUALS SIGN ("="), then advance position to the next character. Otherwise, jump to the last step.

  17. Skip whitespace.

  18. Let url be equal to the substring of input from the character at position to the end of the string.

  19. Strip any trailing space characters from the end of url.

  20. Strip any U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), and U+000D CARRIAGE RETURN (CR) characters from url.

  21. Resolve the url value to an absolute URI using the base URI of the meta element.

  22. Set a timer so that in time seconds, if the user has not canceled the redirect, the user agent navigates to url, with replacement enabled.

For meta elements in the Refresh state, the content attribute must have a value consisting either of:

In the former case, the integer represents a number of seconds before the page is to be reloaded; in the latter case the integer represents a number of seconds before the page is to be replaced by the page at the given URI.

Default style state
  1. ...
3.7.5.4. Specifying the document's character encoding

The meta element may also be used to provide UAs with character encoding information for HTML files, by setting the charset attribute to the name of a character encoding. This is called a character encoding declaration.

The following restrictions apply to character encoding declarations:

If the document does not start with a BOM, and if its encoding is not explicitly given by Content-Type metadata, then the character encoding used must be a superset of US-ASCII (specifically, ANSI_X3.4-1968) for bytes in the range 0x09 - 0x0D, 0x20, 0x21, 0x22, 0x26, 0x27, 0x2C - 0x3F, 0x41 - 0x5A, and 0x61 - 0x7A , and, in addition, if that encoding isn't US-ASCII itself, then the encoding must be specified using a meta element with a charset attribute.

Authors should not use JIS_X0212-1990, x-JIS0208, and encodings based on EBCDIC. Authors should not use UTF-32. Authors must not use the CESU-8, UTF-7, BOCU-1 and SCSU encodings. [CESU8] [UTF7] [BOCU1] [SCSU]

Authors are encouraged to use UTF-8. Conformance checkers may advise against authors using legacy encodings.

In XHTML, the XML declaration should be used for inline character encoding information, if necessary.

3.7.6. The style element

Metadata element.

Contexts in which this element may be used:
If the scoped attribute is absent: in a head element.
If the scoped attribute is absent: in a noscript element that is a child of a head element.
If the scoped attribute is present: at the start of article, aside, div, and section elements.
Content model:
Depends on the value of the type attribute.
Element-specific attributes:
media
type
scoped
Also, the title attribute has special semantics on this element.
DOM interface:
interface HTMLStyleElement : HTMLElement {
           attribute boolean disabled;
           attribute DOMString media;
           attribute DOMString type;
           attribute boolean scoped;
};

The LinkStyle interface must also be implemented by this element, the styling processing model defines how. [CSSOM]

The style element allows authors to embed style information in their documents. The style element is one of several inputs to the styling processing model.

If the type attribute is given, it must contain a valid MIME type, optionally with parameters, that designates a styling language. [RFC2046] If the attribute is absent, the type defaults to text/css. [RFC2138]

When examining types to determine if they support the language, user agents must not ignore unknown MIME parameters — types with unknown parameters must be assumed to be unsupported.

The media attribute says which media the styles apply to. The value must be a valid media query. [MQ] User agents must only apply the styles to views while their state match the listed media. [DOM3VIEWS]

The default, if the media attribute is omitted, is all, meaning that by default styles apply to all media.

The scoped attribute is a boolean attribute. If the attribute is present, then the user agent must only apply the specified style information to the style element's parent element (if any), and that element's child nodes. Otherwise, the specified styles must, if applied, be applied to the entire document.

If the scoped attribute is not specified, the style element must be the child of a head element or of a noscript element that is a child of a head element.

If the scoped attribute is specified, then the style element must be the child of an article, aside, div, or section element, before any significant text or any elements other than style elements.

The title attribute on style elements defines alternative style sheet sets. If the style element has no title attribute, then it has no title; the title attribute of ancestors does not apply to the style element.

The title attribute on style elements, like the title attribute on link elements, differs from the global title attribute in that a style block without a title does not inherit the title of the parent element: it merely has no title.

All descendant elements must be processed, according to their semantics, before the style element itself is evaluated. For styling languages that consist of pure text, user agents must evaluate style elements by passing the concatenation of the contents of all the text nodes that are direct children of the style element (not any other nodes such as comments or elements), in tree order, to the style system. For XML-based styling languages, user agents must pass all the children nodes of the style element to the style system.

This specification does not specify a style system, but CSS is expected to be supported by most Web browsers. [CSS21]

The media, type and scoped DOM attributes must reflect the respective content attributes of the same name.

The DOM disabled attribute behaves as defined for the alternative style sheets DOM.

3.7.7. Styling

The link and style elements can provide styling information for the user agent to use when rendering the document. The DOM Styling specification specifies what styling information is to be used by the user agent and how it is to be used. [CSSOM]

The style and link elements implement the LinkStyle interface. [CSSOM]

For style elements, if the user agent does not support the specified styling language, then the sheet attribute of the element's LinkStyle interface must return null. Similarly, link elements that do not represent external resource links that contribute to the styling processing model (i.e. that do not have a stylesheet keyword in their rel attribute), and link elements whose specified resource has not yet been downloaded, or is not in a supported styling language, must have their LinkStyle interface's sheet attribute return null.

Otherwise, the LinkStyle interface's sheet attribute must return a StyleSheet object with the attributes implemented as follows: [CSSOM]

The content type (type DOM attribute)

The content type must be the same as the style's specified type. For style elements, this is the same as the type content attribute's value, or text/css if that is omitted. For link elements, this is the Content-Type metadata of the specified resource.

The location (href DOM attribute)

For link elements, the location must be the URI given by the element's href content attribute. For style elements, there is no location.

The intended destination media for style information (media DOM attribute)

The media must be the same as the value of the element's media content attribute.

The style sheet title (title DOM attribute)

The title must be the same as the value of the element's title content attribute. If the attribute is absent, then the style sheet does not have a title. The title is used for defining alternative style sheet sets.

The disabled DOM attribute on link and style elements must return false and do nothing on setting, if the sheet attribute of their LinkStyle interface is null. Otherwise, it must return the value of the StyleSheet interface's disabled attribute on getting, and forward the new value to that same attribute on setting.

3.8. Sections

Sectioning elements are elements that divide the page into, for lack of a better word, sections. This section describes HTML's sectioning elements and elements that support them.

Some elements are scoped to their nearest ancestor sectioning element. For example, address elements apply just to their section. For such elements x, the elements that apply to a sectioning element e are all the x elements whose nearest sectioning element is e.

3.8.1. The body element

Sectioning element.

Contexts in which this element may be used:
As the second element in an html element.
Content model:
Zero or more block-level elements.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The body element represents the main content of the document.

The body element potentially has a heading. See the section on headings and sections for further details.

In conforming documents, there is only one body element. The document.body DOM attribute provides scripts with easy access to a document's body element.

Some DOM operations (for example, parts of the drag and drop model) are defined in terms of "the body element". This refers to a particular element in the DOM, as per the definition of the term, and not any arbitrary body element.

3.8.2. The section element

Sectioning block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Zero or more style elements, followed by zero or more block-level elements.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The section element represents a generic document or application section. A section, in this context, is a thematic grouping of content, typically with a header, possibly with a footer.

Examples of sections would be chapters, the various tabbed pages in a tabbed dialog box, or the numbered sections of a thesis. A Web site's home page could be split into sections for an introduction, news items, contact information.

Each section element potentially has a heading. See the section on headings and sections for further details.

3.8.3. The nav element

Sectioning block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Zero or more block-level elements, or inline-level content (but not both).
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The nav element represents a section of a page that links to other pages or to parts within the page: a section with navigation links.

When used as an inline-level content container, the element represents a paragraph.

Each nav element potentially has a heading. See the section on headings and sections for further details.

3.8.4. The article element

Sectioning block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Zero or more style elements, followed by zero or more block-level elements.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The article element represents a section of a page that consists of a composition that forms an independent part of a document, page, or site. This could be a forum post, a magazine or newspaper article, a Web log entry, a user-submitted comment, or any other independent item of content.

An article element is "independent" in that its contents could stand alone, for example in syndication. However, the element is still associated with its ancestors; for instance, contact information that applies to a parent body element still covers the article as well.

When article elements are nested, the inner article elements represent articles that are in principle related to the contents of the outer article. For instance, a Web log entry on a site that accepts user-submitted comments could represent the comments as article elements nested within the article element for the Web log entry.

Author information associated with an article element (q.v. the address element) does not apply to nested article elements.

Each article element potentially has a heading. See the section on headings and sections for further details.

3.8.5. The blockquote element

Sectioning block-level element, and structured inline-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Where structured inline-level elements are allowed.
Content model:
Zero or more block-level elements.
Element-specific attributes:
cite
DOM interface:
interface HTMLQuoteElement : HTMLElement {
           attribute DOMString cite;
};

The HTMLQuoteElement interface is also used by the q element.

The blockquote element represents a section that is quoted from another source.

Content inside a blockquote must be quoted from another source, whose URI, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a URI (or IRI). User agents should allow users to follow such citation links.

If a blockquote element is preceeded or followed by a p element that contains a single cite element and is itself not preceeded or followed by another blockquote element and does not itself have a q element descendant, then, the citation given by that cite element gives the source of the quotation contained in the blockquote element.

Each blockquote element potentially has a heading. See the section on headings and sections for further details.

The cite DOM attribute reflects the element's cite content attribte.

The best way to represent a conversation is not with the cite and blockquote elements, but with the dialog element.

3.8.6. The aside element

Sectioning block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Zero or more style elements, followed by either zero or more block-level elements, or inline-level content (but not both).
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The aside element represents a section of a page that consists of content that is tangentially related to the content around the aside element, and which could be considered separate from that content. Such sections are often represented as sidebars in printed typography.

When used as an inline-level content container, the element represents a paragraph.

Each aside element potentially has a heading. See the section on headings and sections for further details.

3.8.7. The h1, h2, h3, h4, h5, and h6 elements

Block-level elements.

Contexts in which these elements may be used:
Where block-level elements are expected.
Content model:
Significant strictly inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

These elements define headers for their sections.

The semantics and meaning of these elements are defined in the section on headings and sections.

These elements have a rank given by the number in their name. The h1 element is said to have the highest rank, the h6 element has the lowest rank, and two elements with the same name have equal rank.

These elements must not be empty.

3.8.8. The header element

Block-level element.

Contexts in which this element may be used:
Where block-level elements are expected and there are no header ancestors.
Content model:
Zero or more block-level elements, including at least one descendant h1, h2, h3, h4, h5, or h6 element, but no sectioning element descendants, no header element descendants, and no footer element descendants.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The header element represents the header of a section. Headers may contain more than just the section's heading — for example it would be reasonable for the header to include version history information.

header elements must not contain any header elements, footer elements, or any sectioning elements (such as section) as descendants.

header elements must have at least one h1, h2, h3, h4, h5, or h6 element as a descendant.

For the purposes of document summaries, outlines, and the like, header elements are equivalent to the highest ranked h1-h6 element descendant (the first such element if there are multiple elements with that rank).

Other heading elements indicate subheadings or subtitles.

Here are some examples of valid headers. In each case, the emphasised text represents the text that would be used as the header in an application extracting header data and ignoring subheadings.

<header>
 <h1>The reality dysfunction</h1>
 <h2>Space is not the only void</h2>
</header>
<header>
 <p>Welcome to...</p>
 <h1>Voidwars!</h1>
</header>
<header>
 <h1>Scalable Vector Graphics (SVG) 1.2</h1>
 <h2>W3C Working Draft 27 October 2004</h2>
 <dl>
  <dt>This version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20041027/">http://www.w3.org/TR/2004/WD-SVG12-20041027/</a></dd>
  <dt>Previous version:</dt>
  <dd><a href="http://www.w3.org/TR/2004/WD-SVG12-20040510/">http://www.w3.org/TR/2004/WD-SVG12-20040510/</a></dd>
  <dt>Latest version of SVG 1.2:</dt>
  <dd><a href="http://www.w3.org/TR/SVG12/">http://www.w3.org/TR/SVG12/</a></dd>
  <dt>Latest SVG Recommendation:</dt>
  <dd><a href="http://www.w3.org/TR/SVG/">http://www.w3.org/TR/SVG/</a></dd>
  <dt>Editor:</dt>
  <dd>Dean Jackson, W3C, <a href="mailto:dean@w3.org">dean@w3.org</a></dd>
  <dt>Authors:</dt>
  <dd>See <a href="#authors">Author List</a></dd>
 </dl>
 <p class="copyright"><a href="http://www.w3.org/Consortium/Legal/ipr-notic ...
</header>

The section on headings and sections defines how header elements are assigned to individual sections.

The rank of a header element is the same as for an h1 element (the highest rank).

Block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Either zero or more block-level elements, but with no h1, h2, h3, h4, h5, h6, header, or footer elements as descendants, and with no sectioning elements as descendants; or, inline-level content (but not both).
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The footer element represents the footer for the section it applies to. A footer typically contains information about its section such as who wrote it, links to related documents, copyright data, and the like.

footer elements must not contain any footer, header, h1, h2, h3, h4, h5, or h6 elements, or any of the sectioning elements (such as section), as descendants.

When used as an inline-level content container, the element represents a paragraph.

Contact information for the section given in a footer should be marked up using the address element.

3.8.10. The address element

Block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The address element represents a paragraph of contact information for the section it applies to.

For example, a page at the W3C Web site related to HTML might include the following contact information:

<ADDRESS>
 <A href="../People/Raggett/">Dave Raggett</A>, 
 <A href="../People/Arnaud/">Arnaud Le Hors</A>, 
 contact persons for the <A href="Activity">W3C HTML Activity</A>
</ADDRESS>

The address element must not be used to represent arbitrary addresses (e.g. postal addresses), unless those addresses are contact information for the section. (The p element is the appropriate element for marking up such addresses.)

The address element must not contain information other than contact information.

For example, the following is non-conforming use of the address element:

<ADDRESS>Last Modified: 1999/12/24 23:37:50</ADDRESS>

Typically, the address element would be included with other information in a footer element.

To determine the contact information for a sectioning element (such as a document's body element, which would give the contact information for the page), UAs must collect all the address elements that apply to that sectioning element and its ancestor sectioning elements. The contact information is the collection of all the information given by those elements.

Contact information for one sectioning element, e.g. a aside element, does not apply to its ancestor elements, e.g. the page's body.

3.8.11. Headings and sections

The h1-h6 elements and the header element are headings.

The first heading in a sectioning element gives the header for that section. Subsequent headers of equal or higher rank start new (implied) sections, headers of lower rank start subsections that are part of the previous one.

Sectioning elements other than blockquote are always considered subsections of their nearest ancestor sectioning element, regardless of what implied sections other headings may have created. However, blockquote elements are associated with implied sections. Effectively, blockquote elements act like sections on the inside, and act opaquely on the outside.

For the following fragment:

<body>
 <h1>Foo</h1>
 <h2>Bar</h2>
 <blockquote>
  <h3>Bla</h3>
 </blockquote>
 <p>Baz</p>
 <h2>Quux</h2>
 <section>
  <h3>Thud</h3>
 </section>
 <p>Grunt</p>
</body>

...the structure would be:

  1. Foo (heading of explicit body section)
    1. Bar (heading starting implied section)
      1. Bla (heading of explicit blockquote section)
      Baz (paragraph)
    2. Quux (heading starting implied section)
    3. Thud (heading of explicit section section)
    Grunt (paragraph)

Notice how the blockquote nests inside an implicit section while the section does not (and in fact, ends the earlier implicit section so that a later paragraph is back at the top level).

Sections may contain headers of any rank, but authors are strongly encouraged to either use only h1 elements, or to use elements of the appropriate rank for the section's nesting level.

Authors are also encouraged to explictly wrap sections in sectioning elements, instead of relying on the implicit sections generated by having multiple heading in one sectioning element.

For example, the following is correct:

<body>
 <h4>Apples</h4>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <h6>Sweet</h6>
  <p>Red apples are sweeter than green ones.</p>
  <h1>Color</h1>
  <p>Apples come in various colors.</p>
 </section>
</body>

However, the same document would be more clearly expressed as:

<body>
 <h1>Apples</h1>
 <p>Apples are fruit.</p>
 <section>
  <h2>Taste</h2>
  <p>They taste lovely.</p>
  <section>
   <h3>Sweet</h3>
   <p>Red apples are sweeter than green ones.</p>
  </section>
 </section>
 <section>
  <h2>Color</h2>
  <p>Apples come in various colors.</p>
 </section>
</body>

Both of the documents above are semantically identical and would produce the same outline in compliant user agents.

3.8.11.1. Creating an outline

Documents can be viewed as a tree of sections, which defines how each element in the tree is semantically related to the others, in terms of the overall section structure. This tree is related to the document tree, but there is not a one-to-one relationship between elements in the DOM and the document's sections.

The tree of sections should be used when generating document outlines, for example when generating tables of contents.

To derive the tree of sections from the document tree, a hypothetical tree is used, consisting of a view of the document tree containing only the h1-h6 and header elements, and the sectioning elements other than blockquote. Descendants of h1-h6, header, and blockquote elements must be removed from this view.

The hypothetical tree must be rooted at the root element or at a sectioning element. In particular, while the sections inside blockquotes do not contribute to the document's tree of sections, blockquotes can have outlines of their own.

UAs must take this hypothetical tree (which will become the outline) and mutate it by walking it depth first in tree order and, for each h1-h6 or header element that is not the first element of its parent sectioning element, inserting a new sectioning element, as follows:

If the element is a header element, or if it is an h1-h6 node of rank equal to or higher than the first element in the parent sectioning element (assuming that is also an h1-h6 node), or if the first element of the parent sectioning element is a sectioning element:
Insert the new sectioning element as the immediately following sibling of the parent sectioning element, and move all the elements from the current heading element up to the end of the parent sectioning element into the new sectioning element.
Otherwise:
Move the current heading element, and all subsequent siblings up to but excluding the next sectioning element, header element, or h1-h6 of equal or higher rank, whichever comes first, into the new sectioning element, then insert the new sectioning element where the current header was.

The outline is then the resulting hypothetical tree. The ranks of the headers become irrelevant at this point: each sectioning element in the hypothetical tree contains either no or one heading element child. If there is one, then it gives the section's heading, of there isn't, the section has no heading.

Sections are nested as in the hypothetical tree. If a sectioning element is a child of another, that means it is a subsection of that other section.

When creating an interactive table of contents, entries should jump the user to the relevant section element, if it was a real element in the original document, or to the heading, if the section element was one of those created during the above process.

Selecting the first section of the document therefore always takes the user to the top of the document, regardless of where the first header in the body is to be found.

The hypothetical tree (before mutations) could be generated by creating a TreeWalker with the following NodeFilter (described here as an anonymous ECMAScript function). [DOMTR] [ECMA262]

function (n) {
  // This implementation only knows about HTML elements.
  // An implementation that supports other languages might be
  // different.

  // Reject anything that isn't an element.
  if (n.nodeType != Node.ELEMENT_NODE)
    return NodeFilter.FILTER_REJECT;

  // Skip any descendants of headings.
  if ((n.parentNode && n.parentNode.namespaceURI == 'http://www.w3.org/1999/xhtml') &&
      (n.parentNode.localName == 'h1' || n.parentNode.localName == 'h2' ||
       n.parentNode.localName == 'h3' || n.parentNode.localName == 'h4' ||
       n.parentNode.localName == 'h5' || n.parentNode.localName == 'h6' ||
       n.parentNode.localName == 'header'))
    return NodeFilter.FILTER_REJECT;

  // Skip any blockquotes.
  if ((n.namespaceURI == 'http://www.w3.org/1999/xhtml') &&
      (n.localName == 'blockquote'))
    return NodeFilter.FILTER_REJECT;

  // Accept HTML elements in the list given in the prose above.
  if ((n.namespaceURI == 'http://www.w3.org/1999/xhtml') &&
      (n.localName == 'body' || /*n.localName == 'blockquote' ||*/
       n.localName == 'section' || n.localName == 'nav' ||
       n.localName == 'article' || n.localName == 'aside' ||
       n.localName == 'h1' || n.localName == 'h2' ||
       n.localName == 'h3' || n.localName == 'h4' ||
       n.localName == 'h5' || n.localName == 'h6' ||
       n.localName == 'header'))
    return NodeFilter.FILTER_ACCEPT;

  // Skip the rest.
  return NodeFilter.FILTER_SKIP;
}
3.8.11.2. Determining which heading and section applies to a particular node

Given a particular node, user agents must use the following algorithm, in the given order, to determine which heading and section the node is most closely associated with. The processing of this algorithm must stop as soon as the associated section and heading are established (even if they are established to be nothing).

  1. If the node has an ancestor that is a header element, then the associated heading is the most distant such ancestor. The associated section is that header's associated section (i.e. repeat this algorithm for that header).
  2. If the node has an ancestor that is an h1-h6 element, then the associated heading is the most distant such ancestor. The associated section is that heading's section (i.e. repeat this algorithm for that heading element).
  3. If the node is an h1-h6 element or a header element, then the associated heading is the element itself. The UA must then generate the hypothetical section tree described in the previous section, rooted at the nearest section ancestor (or the root element if there is no such ancestor). If the parent of the heading in that hypothetical tree is an element in the real document tree, then that element is the associated section. Otherwise, there is no associated section element.
  4. If the node is a sectioning element, then the associated section is itself. The UA must then generate the hypothetical section tree described in the previous section, rooted at the section itself. If the section element, in that hypothetical tree, has a child element that is an h1-h6 element or a header element, then that element is the associated heading. Otherwise, there is no associated heading element.
  5. If the node is a footer or address element, then the associated section is the nearest ancestor sectioning element, if there is one. The node's associated heading is the same as that sectioning element's associated heading (i.e. repeat this algorithm for that sectioning element). If there is no ancestor sectioning element, the element has no associated section nor an associated heading.
  6. Otherwise, the node is just a normal node, and the document has to be examined more closely to determine its section and heading. Create a view rooted at the nearest ancestor sectioning element (or the root element if there is none) that has just h1-h6 elements, header elements, the node itself, and sectioning elements other than blockquote elements. (Descendants of any of the nodes in this view can be ignored, as can any node later in the tree than the node in question, as the algorithm below merely walks backwards up this view.)
  7. Let n be an iterator for this view, initialised at the node in question.
  8. Let c be the current best candidate heading, initially null, and initially not used. It is used when top-level heading candidates are to be searched for (see below).
  9. Repeat these steps (which effectively goes backwards through the node's previous siblings) until an answer is found:
    1. If n points to a node with no previous sibling, and c is null, then return the node's parent node as the answer. If the node has no parent node, return null as the answer.
    2. Otherwise, if n points to a node with no previous sibling, return c as the answer.
    3. Adjust n so that it points to the previous sibling of the current position.
    4. If n is pointing at an h1 or header element, then return that element as the answer.
    5. If n is pointing at an h2-h6 element, and heading candidates are not being searched for, then return that element as the answer.
    6. Otherwise, if n is pointing at an h2-h6 element, and either c is still null, or c is a heading of lower rank than this one, then set c to be this element, and continue going backwards through the previous siblings.
    7. If n is pointing at a sectioning element, then from this point on top-level heading candidates are being searched for. (Specifically, we are looking for the nearest top-level header for the current section.) Continue going backwards through the previous siblings.
  10. If the answer from the previous step (the loop) is null, which can only happen if the node has no preceeding headings and is not contained in a sectioning element, then there is no associated heading and no associated section.
  11. Otherwise, if the answer from the earlier loop step is a sectioning element, then the associated section is that element and the associated heading is that sectioning element's associated heading (i.e. repeat this algorithm for that section).
  12. Otherwise, if the answer from that same earlier step is an h1-h6 element or a header element, then the associated heading is that element and the associated section is that heading element's associated section (i.e. repeat this algorithm for that heading).

Not all nodes have an associated header or section. For example, if a section is implied, as when multiple headers are found in one sectioning element, then a node in that section has an anonymous associated section (its section is not represented by a real element), and the algorithm above does not associate that node with any particular sectioning element.

For the following fragment:

<body>
 <h1>X</h1>
 <h2>X</h2>
 <blockquote>
  <h3>X</h3>
 </blockquote>
 <p id="a">X</p>
 <h4>Text Node A</h4>
 <section>
  <h5>X</h5>
 </section>
 <p>Text Node B</p>
</body>

The associations are as follows (not all associations are shown):

Node Associated heading Associated section
<body> <h1> <body>
<h1> <h1> <body>
<h2> <h2> None.
<blockquote> <h2> None.
<h3> <h3> <blockquote>
<p id="a"> <h2> None.
Text Node A <h4> None.
Text Node B <h1> <body>
3.8.11.3. Distinguishing site-wide headers from page headers

Given the hypothetical section tree, but ignoring any sections created for nav and aside elements, and any of their descendants, if the root of the tree is the body element's section, and it has only a single subsection which is created by an article element, then the header of the body element should be assumed to be a site-wide header, and the header of the article element should be assumed to be the page's header.

If a page starts with a heading that is common to the whole site, the document must be authored such that, in the document's hypothetical section tree, ignoring any sections created for nav and aside elements and any of their descendants, the root of the tree is the body element's section, its heading is the site-wide heading, the body element has just one subsection, that subsection is created by an article element, and that article's header is the page heading.

If a page does not contain a site-wide heading, then the page must be authored such that, in the document's hypothetical section tree, ignoring any sections created for nav and aside elements and any of their descendants, either the body element has no subsections, or it has more than one subsection, or it has a single subsection but that subsection is not created by an article element.

Conceptually, a site is thus a document with many articles — when those articles are split into many pages, the heading of the original single page becomes the heading of the site, repeated on every page.

3.9. Prose

3.9.1. The p element

Block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Significant inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The p element represents a paragraph.

p elements can contain a mixture of strictly inline-level content, such as text, images, hyperlinks, etc, and structured inline-level elements, such as lists, tables, and block quotes. p elements must not be empty.

The following examples are conforming HTML fragments:

<p>The little kitten gently seated himself on a piece of
carpet. Later in his life, this would be referred to as the time the
cat sat on the mat.</p>
<fieldset>
 <legend>Personal information</legend>
 <p>
   <label>Name: <input name="n"></label>
   <label><input name="anon" type="checkbox"> Hide from other users</label>
 </p>
 <p><label>Address: <textarea name="a"></textarea></label></p>
</fieldset>
<p>There was once an example from Femley,<br>
Whose markup was of dubious quality.<br>
The validator complained,<br>
So the author was pained,<br>
To move the error from the markup to the rhyming.</p>

The p element should not be used when a more specific element is more appropriate.

The following example is technically correct:

<section>
 <!-- ... -->
 <p>Last modified: 2001-04-23</p>
 <p>Author: fred@example.com</p>
</section>

However, it would be better marked-up as:

<section>
 <!-- ... -->
 <footer>Last modified: 2001-04-23</footer>
 <address>Author: fred@example.com</address>
</section>

Or:

<section>
 <!-- ... -->
 <footer>
  <p>Last modified: 2001-04-23</p>
  <address>Author: fred@example.com</address>
 </footer>
</section>

3.9.2. The hr element

Block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Empty.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The hr element represents a paragraph-level thematic break, e.g. a scene change in a story, or a transition to another topic within a section of a reference book.

3.9.3. The br element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Empty.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The br element represents a line break.

br elements must be empty. Any content inside br elements must not be considered part of the surrounding text.

br elements must only be used for line breaks that are actually part of the content, as in poems or addresses.

The following example is correct usage of the br element:

<p>P. Sherman<br>
42 Wallaby Way<br>
Sydney</p>

br elements must not be used for separating thematic groups in a paragraph.

The following examples are non-conforming, as they abuse the br element:

<p><a ...>34 comments.</a><br>
<a ...>Add a comment.<a></p>
<p>Name: <input name="name"><br>
Address: <input name="address"></p>

Here are alternatives to the above, which are correct:

<p><a ...>34 comments.</a></p>
<p><a ...>Add a comment.<a></p>
<p>Name: <input name="name"></p>
<p>Address: <input name="address"></p>

3.9.4. The dialog element

Block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
Zero or more pairs of dt and dd elements.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The dialog element represents a conversation.

Each part of the conversation must have an explicit talker (or speaker) given by a dt element, and a discourse (or quote) given by a dd element.

This example demonstrates this using an extract from Abbot and Costello's famous sketch, Who's on first:

<dialog>
 <dt> Costello
 <dd> Look, you gotta first baseman?
 <dt> Abbott
 <dd> Certainly.
 <dt> Costello
 <dd> Who's playing first?
 <dt> Abbott
 <dd> That's right.
 <dt> Costello
 <dd> When you pay off the first baseman every month, who gets the money?
 <dt> Abbott
 <dd> Every dollar of it. 
</dialog>

Text in a dt element in a dialog element is implicitly the source of the text given in the following dd element, and the contents of the dd element are implicitly a quote from that speaker. There is thus no need to include cite, q, or blockquote elements in this markup. Indeed, a q element inside a dd element in a conversation would actually imply the person talking were themselves quoting someone else. See the cite, q, and blockquote elements for other ways to cite or quote.

3.10. Preformatted text

3.10.1. The pre element

Block-level element, and structured inline-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Where structured inline-level elements are allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The pre element represents a block of preformatted text, in which structure is represented by typographic conventions rather than by elements.

Some examples of cases where the pre element could be used:

If, ignoring text nodes consisting only of whitespace, the only child of a pre is a code element, then the pre element represents a block of computer code.

If, ignoring text nodes consisting only of whitespace, the only child of a pre is a samp element, then the pre element represents a block of computer output.

3.11. Lists

3.11.1. The ol element

Block-level element, and structured inline-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Where structured inline-level elements are allowed.
Content model:
Zero or more li elements.
Element-specific attributes:
start
DOM interface:
interface HTMLOListElement : HTMLElement {
           attribute long start;
};

The ol element represents an ordered list of items (which are represented by li elements).

The start attribute, if present, must be a valid integer giving the ordinal value of the first list item.

If the start attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. The default value, used if the attribute is missing or if the value cannot be converted to a number according to the referenced algorithm, is 1.

The items of the list are the li element child nodes of the ol element, in tree order.

The first item in the list has the ordinal value given by the ol element's start attribute, unless that li element has a value attribute with a value that can be successfully parsed, in which case it has the ordinal value given by that value attribute.

Each subsequent item in the list has the ordinal value given by its value attribute, if it has one, or, if it doesn't, the ordinal value of the previous item, plus one.

The start DOM attribute must reflect the value of the start content attribute.

3.11.2. The ul element

Block-level element, and structured inline-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Where structured inline-level elements are allowed.
Content model:
Zero or more li elements.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The ul element represents an unordered list of items (which are represented by li elements).

The items of the list are the li element child nodes of the ul element.

3.11.3. The li element

Contexts in which this element may be used:
Inside ol elements.
Inside ul elements.
Inside menu elements.
Content model:
When the element is a child of an ol or ul element and the grandchild of an element that is being used as an inline-level content container, or, when the element is a child of a menu element: inline-level content.
Otherwise: zero or more block-level elements, or inline-level content (but not both).
Element-specific attributes:
If the element is a child of an ol element: value
If the element is not the child of an ol element: None.
DOM interface:
interface HTMLLIElement : HTMLElement {
           attribute long value;
};

The li element represents a list item. If its parent element is an ol, ul, or menu element, then the element is an item of the parent element's list, as defined for those elements. Otherwise, the list item has no defined list-related relationship to any other li element.

When the list item is the child of an ol or ul element, the content model of the item depends on the way that parent element was used. If it was used as structured inline content (i.e. if that element's parent was used as an inline-level content container), then the li element must only contain inline-level content. Otherwise, the element may be used either for inline content or block-level elements.

When the list item is the child of a menu element, the li element must contain only inline-level content.

When the list item is not the child of an ol, ul, or menu element, e.g. because it is an orphaned node not in the document, it may contain either for inline content or block-level elements.

When used as an inline-level content container, the list item represents a single paragraph.

The value attribute, if present, must be a valid integer giving the ordinal value of the first list item.

If the value attribute is present, user agents must parse it as an integer, in order to determine the attribute's value. If the attribute's value cannot be converted to a number, it must be treated as if the attribute was absent. The attribute has no default value.

The value attribute is processed relative to the element's parent ol element (q.v.), if there is one. If there is not, the attribute has no effect.

The value DOM attribute must reflect the value of the value content attribute.

3.11.4. The dl element

Block-level element, and structured inline-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Where structured inline-level elements are allowed.
Content model:
Zero or more groups each consisting of one or more dt elements followed by one or mode dd elements.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The dl element introduces an unordered association list consisting of zero or more name-value groups (a description list). Each group must consist of one or more names (dt elements) followed by one or more values (dd elements).

Name-value groups may be terms and definitions, metadata topics and values, or any other groups of name-value data.

The following are all conforming HTML fragments.

In the following example, one entry ("Authors") is linked to two values ("John" and "Luke").

<dl>
 <dt> Authors
 <dd> John
 <dd> Luke
 <dt> Editor
 <dd> Frank
</dl>

In the following example, one definition is linked to two terms.

<dl>
 <dt lang="en-US"> <dfn>color</dfn> </dt>
 <dt lang="en-GB"> <dfn>colour</dfn> </dt>
 <dd> A sensation which (in humans) derives from the ability of
 the fine structure of the eye to distinguish three differently
 filtered analyses of a view. </dd>
</dl>

The following example illustrates the use of the dl element to mark up metadata of sorts. At the end of the example, one group has two metadata labels ("Authors" and "Editors") and two values ("Robert Rothman" and "Daniel Jackson").

<dl>
 <dt> Last modified time </dt>
 <dd> 2004-12-23T23:33Z </dd>
 <dt> Recommended update interval </dt>
 <dd> 60s </dd>
 <dt> Authors </dt>
 <dt> Editors </dt>
 <dd> Robert Rothman </dd>
 <dd> Daniel Jackson </dd>
</dl>

If a dl element is empty, it contains no groups.

If a dl element contains non-whitespace text nodes, or elements other than dt and dd, then those elements or text nodes do not form part of any groups in that dl, and the document is non-conforming.

If a dl element contains only dt elements, then it consists of one group with names but no values, and the document is non-conforming.

If a dl element contains only dd elements, then it consists of one group with values but no names, and the document is non-conforming.

The dl element is inappropriate for marking up dialogue, since dialogue is ordered (each speaker/line pair comes after the next). For an example of how to mark up dialogue, see the dialog element.

3.11.5. The dt element

Contexts in which this element may be used:
Before dd or dt elements inside dl elements.
Before a dd element inside a dialog element.
Content model:
Strictly inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The dt element represents the term, or name, part of a term-description group in a description list (dl element), and the talker, or speaker, part of a talker-discourse pair in a conversation (dialog element).

The dt element itself, when used in a dl element, does not indicate that its contents are a term being defined, but this can be indicated using the dfn element.

3.11.6. The dd element

Contexts in which this element may be used:
After dt or dd elements inside dl elements.
After a dt element inside a dialog element.
Content model:
When the element is a child of a dl element and the grandchild of an element that is being used as an inline-level content container: inline-level content.
Otherwise: zero or more block-level elements, or inline-level content (but not both).
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The dd element represents the description, definition, or value, part of a term-description group in a description list (dl element), and the discourse, or quote, part in a conversation (dialog element).

The content model of a dd element depends on the way its parent element is being used. If the parent element is a dl element that is being used as structured inline content (i.e. if the dl element's parent element is being used as an inline-level content container), then the dd element must only contain inline-level content.

Otherwise, the element may be used either for inline content or block-level elements.

3.12. Phrase elements

3.12.1. The a element

Interactive, strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed, if there are no ancestor interactive elements.
Content model:
When used in an element whose content model is only strictly inline-level content: only significant strictly inline-level content, but there must be no interactive descendants.
Otherwise: any significant inline-level content, but there must be no interactive descendants.
Element-specific attributes:
href
target
ping
rel
media
hreflang
type
DOM interface:
interface HTMLAnchorElement : HTMLElement {
           attribute DOMString href;
           attribute DOMString target;
           attribute DOMString ping;
           attribute DOMString rel;
  readonly attribute DOMTokenList relList;
           attribute DOMString media;
           attribute DOMString hreflang;
           attribute DOMString type;
};

The Command interface must also be implemented by this element.

If the a element has an href attribute, then it represents a hyperlink.

If the a element has no href attribute, then the element is a placeholder for where a link might otherwise have been placed, if it had been relevant.

The target, ping, rel, media, hreflang, and type attributes must be omitted if the href attribute is not present.

If a site uses a consistent navigation toolbar on every page, then the link that would normally link to the page itself could be marked up using an a element:

<nav>
 <ul>
  <li> <a href="/">Home</a> </li>
  <li> <a href="/news">News</a> </li>
  <li> <a>Examples</a> </li>
  <li> <a href="/legal">Legal</a> </li>
 </ul>
</nav>

Interactive user agents should allow users to follow hyperlinks created using the a element. The href, target and ping attributes decide how the link is followed. The rel, media, hreflang, and type attributes may be used to indicate to the user the likely nature of the target resource before the user follows the link.

The activation behavior of a elements that represent hyperlinks is to run the following steps:

  1. If the DOMActivate event in question is not trusted (i.e. a click() method call was the reason for the event being dispatched), and the a element's target attribute is ... then raise an INVALID_ACCESS_ERR exception and abort these steps.

  2. If the target of the DOMActivate event is an img element with an ismap attribute specified, then server-side image map processing must be performed, as follows:

    1. If the DOMActivate event was dispatched as the result of a real pointing-device-triggered click event on the img element, then let x be the distance in CSS pixels from the left edge of the image to the location of the click, and let y be the distance in CSS pixels from the top edge of the image to the location of the click. Otherwise, let x and y be zero.
    2. Let the hyperlink suffix be a U+003F QUESTION MARK character, the value of x expressed as a base-ten integer using ASCII digits (U+0030 DIGIT ZERO to U+0039 DIGIT NINE), a U+002C COMMA character, and the value of y expressed as a base-ten integer using ASCII digits.
  3. Finally, the user agent must follow the hyperlink defined by the a element. If the steps above defined a hyperlink suffix, then take that into account when following the hyperlink.

One way that a user agent can enable users to follow hyperlinks is by allowing a elements to be clicked, or focussed and activated by the keyboard. This will cause the aforementioned activation behavior to be invoked.

The a element must not be empty.

The DOM attributes href, ping, target, rel, media, hreflang, and type, must each reflect the respective content attributes of the same name.

The DOM attribute relList must reflect the rel content attribute.

3.12.2. The q element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.
Otherwise: any inline-level content.
Element-specific attributes:
cite
DOM interface:
The q element uses the HTMLQuoteElement interface.

The q element represents a part of a paragraph quoted from another source.

Content inside a q element must be quoted from another source, whose URI, if it has one, should be cited in the cite attribute.

If the cite attribute is present, it must be a URI (or IRI). User agents should allow users to follow such citation links.

If a q element is contained (directly or indirectly) in a paragraph that contains a single cite element and has no other q element descendants, then, the citation given by that cite element gives the source of the quotation contained in the q element.

3.12.3. The cite element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The cite element represents a citation: the source, or reference, for a quote or statement made in the document.

A citation is not a quote (for which the q element is appropriate).

This is incorrect usage:

<p><cite>This is wrong!</cite>, said Ian.</p>

This is the correct way to do it:

<p><q>This is correct!</q>, said <cite>Ian</cite>.</p>

This is also wrong, because the title and the name are not references or citations:

<p>My favourite book is <cite>The Reality Dysfunction</cite>
by <cite>Peter F. Hamilton</cite>.</p>

This is correct, because even though the source is not quoted, it is cited:

<p>According to <cite>the Wikipedia article on
HTML</cite>, HTML is defined in formal specifications that were
developed and published throughout the 1990s.</p>

The cite element can apply to blockquote and q elements in certain cases described in the definitions of those elements.

3.12.4. The em element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.
Otherwise: any inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The em element represents stress emphasis of its contents.

The level of emphasis that a particlar piece of content has is given by its number of ancestor em elements.

The placement of emphasis changes the meaning of the sentence. The element thus forms an integral part of the content. The precise way in which emphasis is used in this way depends on the language.

These examples show how changing the emphasis changes the meaning. First, a general statement of fact, with no emphasis:

<p>Cats are cute animals.</p>

By emphasising the first word, the statement implies that the kind of animal under discussion is in question (maybe someone is asserting that dogs are cute):

<p><em>Cats</em> are cute animals.</p>

Moving the emphasis to the verb, one highlights that the truth of the entire sentence is in question (maybe someone is saying cats are not cute):

<p>Cats <em>are</em> cute animals.</p>

By moving it to the adjective, the exact nature of the cats is reasserted (maybe someone suggested cats were mean animals):

<p>Cats are <em>cute</em> animals.</p>

Similarly, if someone asserted that cats were vegetables, someone correcting this might emphasise the last word:

<p>Cats are cute <em>animals</em>.</p>

By emphasising the entire sentence, it becomes clear that the speaker is fighting hard to get the point across. This kind of emphasis also typically affects the punctuation, hence the exclamation mark here.

<p><em>Cats are cute animals!</em></p>

Anger mixed with emphasising the cuteness could lead to markup such as:

<p><em>Cats are <em>cute</em> animals!</em></p>

3.12.5. The strong element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.
Otherwise: any inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The strong element represents strong importance for its contents.

The relative level of importance of a piece of content is given by its number of ancestor strong elements; each strong element increases the importance of its contents.

Changing the importance of a piece of text with the strong element does not change the meaning of the sentence.

Here is an example of a warning notice in a game, with the various parts marked up according to how important they are:

<p><strong>Warning.</strong> This dungeon is dangerous.
<strong>Avoid the ducks.</strong> Take any gold you find.
<strong><strong>Do not take any of the diamonds</strong>,
they are explosive and <strong>will destroy anything within
ten meters.</strong></strong> You have been warned.</p>

3.12.6. The small element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.
Otherwise: any inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The small element represents small print (part of a document often describing legal restrictions, such as copyrights or other disadvantages), or other side comments.

The small element does not "de-emphasise" or lower the importance of text emphasised by the em element or marked as important with the strong element.

In this example the footer contains contact information and a copyright.

<footer>
 <address>
  For more details, contact
  <a href="mailto:js@example.com">John Smith</a>.
 </address>
 <p><small>© copyright 2038 Example Corp.</small></p>
</footer>

In this second example, the small element is used for a side comment.

<p>Example Corp today announced record profits for the
second quarter <small>(Full Disclosure: Foo News is a subsidiary of
Example Corp)</small>, leading to speculation about a third quarter
merger with Demo Group.</p>

In this last example, the small element is marked as being important small print.

<p><strong><small>Continued use of this service will result in a kiss.</small></strong></p>

3.12.7. The m element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.
Otherwise: any inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The m element represents a run of text marked or highlighted.

In the following snippet, a paragraph of text refers to a specific part of a code fragment.

<p>The highlighted part below is where the error lies:</p>
<pre><code>var i: Integer;
begin
   i := <m>1.1</m>;
end.</code></pre>

Another example of the m element is highlighting parts of a document that are matching some search string. If someone looked at a document, and the server knew that the user was searching for the word "kitten", then the server might return the document with one paragraph modified as follows:

<p>I also have some <m>kitten</m>s who are visiting me
these days. They're really cute. I think they like my garden!</p>

3.12.8. The dfn element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed, if there are no ancestor dfn elements.
Content model:
Strictly inline-level content, but there must be no descendant dfn elements.
Element-specific attributes:
None, but the title attribute has special semantics on this element.
DOM interface:
No difference from HTMLElement.

The dfn element represents the defining instance of a term. The paragraph, description list group, or section that contains the dfn element contains the definition for the term given by the contents of the dfn element.

dfn elements must not be nested.

Defining term: If the dfn element has a title attribute, then the exact value of that attribute is the term being defined. Otherwise, if it contains exactly one element child node and no child text nodes, and that child element is an abbr element with a title attribute, then the exact value of that attribute is the term being defined. Otherwise, it is the exact textContent of the dfn element that gives the term being defined.

If the title attribute of the dfn element is present, then it must only contain the term being defined.

There must only be one dfn element per document for each term defined (i.e. there must not be any duplicate terms).

The title attribute of ancestor elements does not affect dfn elements.

The dfn element enables automatic cross-references. Specifically, any span, abbr, code, var, samp, or i element that has a non-empty title attribute whose value exactly equals the term of a dfn element in the same document, or which has no title attribute but whose textContent exactly equals the term of a dfn element in the document, and that has no interactive elements or dfn elements either as ancestors or descendants, and has no other elements as ancestors that are themselves matching these conditions, should be presented in such a way that the user can jump from the element to the first dfn element giving the defining instance of that term.

In the following fragment, the term "GDO" is first defined in the first paragraph, then used in the second. A compliant UA could provide a link from the abbr element in the second paragraph to the dfn element in the first.

<p>The <dfn><abbr title="Garage Door Opener">GDO</abbr></dfn>
is a device that allows off-world teams to open the iris.</p>
<!-- ... later in the document: -->
<p>Teal'c activated his <abbr title="Garage Door Opener">GDO</abbr>
and so Hammond ordered the iris to be opened.</p>

3.12.9. The abbr element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None, but the title attribute has special semantics on this element.
DOM interface:
No difference from HTMLElement.

The abbr element represents an abbreviation or acronym. The title attribute should be used to provide an expansion of the abbreviation. If present, the attribute must only contain an expansion of the abbreviation.

The paragraph below contains an abbreviation marked up with the abbr element.

<p>The <abbr title="Web Hypertext Application Technology
Working Group">WHATWG</abbr> is a loose unofficial collaboration of
Web browser manufacturers and interested parties who wish to develop
new technologies designed to allow authors to write and deploy
Applications over the World Wide Web.</p>

The title attribute may be omitted if there is a dfn element in the document whose defining term is the abbreviation (the textContent of the abbr element).

In the example below, the word "Zat" is used as an abbreviation in the second paragraph. The abbreviation is defined in the first, so the explanatory title attribute has been omitted. Because of the way dfn elements are defined, the second abbr element in this example would be connected (in some UA-specific way) to the first.

<p>The <dfn><abbr>Zat</abbr></dfn>, short for Zat'ni'catel, is a weapon.</p>
<p>Jack used a <abbr>Zat</abbr> to make the boxes of evidence disappear.</p>

3.12.10. The time element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
datetime
DOM interface:
interface HTMLTimeElement : HTMLElement {
           attribute DOMString dateTime;
  readonly attribute DOMTimeStamp date;
  readonly attribute DOMTimeStamp time;
  readonly attribute DOMTimeStamp timezone;
};

The time element represents a date and/or a time.

The datetime attribute, if present, must contain a date or time string that identifies the date or time being specified.

If the datetime attribute is not present, then the date or time must be specified in the content of the element, such that parsing the element's textContent according to the rules for parsing date or time strings in content successfully extracts a date or time.

The dateTime DOM attribute must reflect the datetime content attribute.

User agents, to obtain the date, time, and timezone represented by a time element, must follow the following steps:

  1. If the datetime attribute is present, then parse it according to the rules for parsing date or time strings in content, and let the result be result.
  2. Otherwise, parse the element's textContent according to the rules for parsing date or time strings in content, and let the result be result.
  3. If result is empty (because the parsing failed), then the date is unknown, the time is unknown, and the timezone is unknown.
  4. Otherwise: if result contains a date, then that is the date; if result contains a time, then that is the time; and if result contains a timezone, then the timezone is the element's timezone. (A timezone can only be present if both a date and a time are also present.)

The date DOM attribute must return null if the date is unknown, and otherwise must return the time corresponding to midnight UTC (i.e. the first second) of the given date.

The time DOM attribute must return null if the time is unknown, and otherwise must return the time corresponding to the given time of 1970-01-01, with the timezone UTC.

The timezone DOM attribute must return null if the timezone is unknown, and otherwise must return the time corresponding to 1970-01-01 00:00 UTC in the given timezone, with the timezone set to UTC (i.e. the time corresponding to 1970-01-01 at 00:00 UTC plus the offset corresponding to the timezone).

In the following snippet:

<p>Our first date was <time datetime="2006-09-23">a saturday</time>.</p>

...the time element's date attribute would have the value 1,158,969,600,000ms, and the time and timezone attributes would return null.

In the following snippet:

<p>We stopped talking at <time datetime="2006-09-24 05:00 -7">5am the next morning</time>.</p>

...the time element's date attribute would have the value 1,159,056,000,000ms, the time attribute would have the value 18,000,000ms, and the timezone attribute would return -25,200,000ms. To obtain the actual time, the three attributes can be added together, obtaining 1,159,048,800,000, which is the specified date and time in UTC.

Finally, in the following snippet:

<p>Many people get up at <time>08:00</time>.</p>

...the time element's date attribute would have the value null, the time attribute would have the value 28,800,000ms, and the timezone attribute would return null.

These APIs may be suboptimal. Comments on making them more useful to JS authors are welcome. The primary use cases for these elements are for marking up publication dates e.g. in blog entries, and for marking event dates in hCalendar markup. Thus the DOM APIs are likely to be used as ways to generate interactive calendar widgets or some such.

3.12.11. The meter element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
value
min
low
high
max
optimum
DOM interface:
interface HTMLMeterElement : HTMLElement {
           attribute long value;
           attribute long min;
           attribute long max;
           attribute long low;
           attribute long high;
           attribute long optimum;
};

The meter element represents a scalar measurement within a known range, or a fractional value; for example disk usage, the relevance of a query result, or the fraction of a voting population to have selected a particular candidate.

This is also known as a gauge.

The meter element should not be used to indicate progress (as in a progress bar). For that role, HTML provides a separate progress element.

There are six attributes that determine the semantics of the gauge represented by the element.

The min attribute specifies the lower bound of the range, and the max attribute specifies the upper bound. The value attribute specifies the value to have the gauge indicate as the "measured" value.

The other three attributes can be used to segment the gauge's range into "low", "medium", and "high" parts, and to indicate which part of the gauge is the "optimum" part. The low attribute specifies the range that is considered to be the "low" part, and the high attribute specifies the range that is considered to be the "high" part. The optimum attribute gives the position that is "optimum"; if that is higher than the "high" value then this indicates that the higher the value, the better; if it's lower than the "low" mark then it indicates that lower values are better, and naturally if it is in between then it indicates that neither high nor low values are good.

Authoring requirements: The recommended way of giving the value is to include it as contents of the element, either as two numbers (the higher number represents the maximum, the other number the current value), or as a percentage or similar (using one of the characters such as "%"), or as a fraction.

The value, min, low, high, max, and optimum attributes are all optional. When present, they must have values that are valid floating point numbers.

The following examples all represent a measurement of three quarters (of the maximum of whatever is being measured):

<meter>75%</meter>
<meter>750‰</meter>
<meter>3/4</meter>
<meter>6 blocks used (out of 8 total)</meter>
<meter>max: 100; current: 75</meter>
<meter><object data="graph75.png">0.75</object></meter>
<meter min="0" max="100" value="75"></meter>

User agent requirements: User agents must parse the min, max, value, low, high, and optimum attributes using the rules for parsing floating point number values.

If the value attribute has been omitted, the user agent must also process the textContent of the element according to the steps for finding one or two numbers of a ratio in a string. These steps will return nothing, one number, one number with a denominator punctuation character, or two numbers.

User agents must then use all these numbers to obtain values for six points on the gauge, as follows. (The order in which these are evaluated is important, as some of the values refer to earlier ones.)

The minimum value

If the min attribute is specified and a value could be parsed out of it, then the minimum value is that value. Otherwise, the minimum value is zero.

The maximum value

If the max attribute is specified and a value could be parsed out of it, the maximum value is that value.

Otherwise, if the max attribute is specified but no value could be parsed out of it, or if it was not specified, but either or both of the min or value attributes were specified, then the maximum value is 1.

Otherwise, none of the max, min, and value attributes were specified. If the result of processing the textContent of the element was either nothing or just one number with no denominator punctuation character, then the maximum value is 1; if the result was one number but it had an associated denominator punctuation character, then the maximum value is the value associated with that denominator punctuation character; and finally, if there were two numbers parsed out of the textContent, then the maximum is the higher of those two numbers.

If the above machinations result in a maximum value less than the minimum value, then the maximum value is actually the same as the minimum value.

The actual value

If the value attribute is specified and a value could be parsed out of it, then that value is the actual value.

If the value attribute is not specified but the max attribute is specified and the result of processing the textContent of the element was one number with no associated denominator punctuation character, then that number is the actual value.

If neither of the value and max attributes are specified, then, if the result of processing the textContent of the element was one number (with or without an associated denominator punctuation character), then that is the actual value, and if the result of processing the textContent of the element was two numbers, then the actual value is the lower of the two numbers found.

Otherwise, if none of the above apply, the actual value is zero.

If the above procedure results in an actual value less than the minimum value, then the actual value is actually the same as the minimum value.

If, on the other hand, the result is an actual value greater than the maximum value, then the actual value is the maximum value.

The low boundary

If the low attribute is specified and a value could be parsed out of it, then the low boundary is that value. Otherwise, the low boundary is the same as the minimum value.

If the above results in a low boundary that is less than the minimum value, the low boundary is the minimum value.

The high boundary

If the high attribute is specified and a value could be parsed out of it, then the high boundary is that value. Otherwise, the high boundary is the same as the maximum value.

If the above results in a high boundary that is higher than the maximum value, the high boundary is the maximum value.

The optimum point

If the optimum attribute is specified and a value could be parsed out of it, then the optimum point is that value. Otherwise, the optimum point is the midpoint between the minimum value and the maximum value.

If the optimum point is then less than the minimum value, then the optimum point is actually the same as the minimum value. Similarly, if the optimum point is greater than the maximum value, then it is actually the maximum value instead.

All of which should result in the following inequalities all being true:

UA requirements for regions of the gauge: If the optimum point is equal to the low boundary or the high boundary, or anywhere in between them, then the region between the low and high boundaries of the gauge must be treated as the optimum region, and the low and high parts, if any, must be treated as suboptimal. Otherwise, if the optimum point is less than the low boundary, then the region between the minimum value and the low boundary must be treated as the optimum region, the region between the low boundary and the high boundary must be treated as a suboptimal region, and the region between the high boundary and the maximum value must be treated as an even less good region. Finally, if the optimum point is higher than the high boundary, then the situation is reversed; the region between the high boundary and the maximum value must be treated as the optimum region, the region between the high boundary and the low boundary must be treated as a suboptimal region, and the remaining region between the low boundary and the minimum value must be treated as an even less good region.

UA requirements for showing the gauge: When representing a meter element to the user, the UA should indicate the relative position of the actual value to the minimum and maximum values, and the relationship between the actual value and the three regions of the gauge.

The following markup:

<h3>Suggested groups</h3>
<menu type="toolbar">
 <a href="?cmd=hsg" onclick="hideSuggestedGroups()">Hide suggested groups</a>
</menu>
<ul>
 <li>
  <p><a href="/group/comp.infosystems.www.authoring.stylesheets/view">comp.infosystems.www.authoring.stylesheets</a> -
     <a href="/group/comp.infosystems.www.authoring.stylesheets/subscribe">join</a></p>
  <p>Group description: <strong>Layout/presentation on the WWW.</strong></p>
  <p><meter value="0.5">Moderate activity,</meter> Usenet, 618 subscribers</p>
 </li>
 <li>
  <p><a href="/group/netscape.public.mozilla.xpinstall/view">netscape.public.mozilla.xpinstall</a> -
     <a href="/group/netscape.public.mozilla.xpinstall/subscribe">join</a></p>
  <p>Group description: <strong>Mozilla XPInstall discussion.</strong></p>
  <p><meter value="0.25">Low activity,</meter> Usenet, 22 subscribers</p>
 </li>
 <li>
  <p><a href="/group/mozilla.dev.general/view">mozilla.dev.general</a> -
     <a href="/group/mozilla.dev.general/subscribe">join</a></p>
  <p><meter value="0.25">Low activity,</meter> Usenet, 66 subscribers</p>
 </li>
</ul>

Might be rendered as follows:

With the <meter> elements rendered as inline green bars of
    varying lengths.

The min, max, value, low, high, and optimum DOM attributes must reflect the elements' content attributes of the same name. When the relevant content attributes are absent, the DOM attributes must return zero. The value parsed from the textContent never affects the DOM values.

Would be cool to have the value DOM attribute update the textContent in-line...

3.12.12. The progress element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
value
max
DOM interface:
interface HTMLProgressElement : HTMLElement {
           attribute float value;
           attribute float max;
  readonly attribute float position;
};

The progress element represents the completion progress of a task. The progress is either indeterminate, indicating that progress is being made but that it is not clear how much more work remains to be done before the task is complete (e.g. because the task is waiting for a remote host to respond), or the progress is a number in the range zero to a maximum, giving the fraction of work that has so far been completed.

There are two attributes that determine the current task completion represented by the element.

The value attribute specifies how much of the task has been completed, and the max attribute specifies how much work the task requires in total. The units are arbitrary and not specified.

Instead of using the attributes, authors are recommended to simply include the current value and the maximum value inline as text inside the element.

Here is a snippet of a Web application that shows the progress of some automated task:

<section>
 <h2>Task Progress</h2>
 <p><label>Progress: <progress><span id="p">0</span>%</progress></p>
 <script>
  var progressBar = document.getElementById('p');
  function updateProgress(newValue) {
    progressBar.textContent = newValue;
  }
 </script>
</section>

(The updateProgress() method in this example would be called by some other code on the page to update the actual progress bar as the task progressed.)

Author requirements: The max and value attributes, when present, must have values that are valid floating point numbers. The max attribute, if present, must have a value greater than zero. The value attribute, if present, must have a value equal to or greater than zero, and less than or equal to the value of the max attribute, if present.

User agent requirements: User agents must parse the max and value attributes' values according to the rules for parsing floating point number values.

If the value attribute is omitted, then user agents must also parse the textContent of the progress element in question using the steps for finding one or two numbers of a ratio in a string. These steps will return nothing, one number, one number with a denominator punctuation character, or two numbers.

Using the results of this processing, user agents must determine whether the progress bar is an indeterminate progress bar, or whether it is a determinate progress bar, and in the latter case, what its current and maximum values are, all as follows:

  1. If the max attribute is omitted, and the value is omitted, and the results of parsing the textContent was nothing, then the progress bar is an indeterminate progress bar. Abort these steps.
  2. Otherwise, it is a determinate progress bar.
  3. If the max attribute is included, then, if a value could be parsed out of it, then the maximum value is that value.
  4. Otherwise, if the max attribute is absent but the value attribute is present, or, if the max attribute is present but no value could be parsed from it, then the maximum is 1.
  5. Otherwise, if neither attribute is included, then, if the textContent contained one number with an associated denominator punctuation character, then the maximum value is the value associated with that denominator punctuation character; otherwise, if the textContent contained two numbers, the maximum value is the higher of the two values; otherwise, the maximum value is 1.
  6. If the value attribute is present on the element and a value could be parsed out of it, that value is the current value of the progress bar. Otherwise, if the attribute is present but no value could be parsed from it, the current value is zero.
  7. Otherwise if the value attribute is absent and the max attribute is present, then, if the textContent was parsed and found to contain just one number, with no associated denominator punctuation character, then the current value is that number. Otherwise, if the value attribute is absent and the max attribute is present then the current value is zero.
  8. Otherwise, if neither attribute is present, then the current value is the lower of the one or two numbers that were found in the textContent of the element.
  9. If the maximum value is less than or equal to zero, then it is reset to 1.
  10. If the current value is less than zero, then it is reset to zero.
  11. Finally, if the current value is greater than the maximum value, then the current value is reset to the maximum value.

UA requirements for showing the progress bar: When representing a progress element to the user, the UA should indicate whether it is a determinate or indeterminate progress bar, and in the former case, should indicate the relative position of the current value relative to the maximum value.

The max and value DOM attributes must reflect the elements' content attributes of the same name. When the relevant content attributes are absent, the DOM attributes must return zero. The value parsed from the textContent never affects the DOM values.

Would be cool to have the value DOM attribute update the textContent in-line...

If the progress bar is an indeterminate progress bar, then the position DOM attribute must return -1. Otherwise, it must return the result of dividing the current value by the maximum value.

3.12.13. The code element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.
Otherwise: any inline-level content.
Element-specific attributes:
None, but the title attribute has special semantics on this element when used with the dfn element.
DOM interface:
No difference from HTMLElement.

The code element represents a fragment of computer code. This could be an XML element name, a filename, a computer program, or any other string that a computer would recognise.

See the pre element for more detais.

The following example shows how a block of code could be marked up using the pre and code elements.

<pre><code>var i: Integer;
begin
   i := 1;
end.</code></pre>

3.12.14. The var element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None, but the title attribute has special semantics on this element when used with the dfn element.
DOM interface:
No difference from HTMLElement.

The var element represents a variable. This could be an actual variable in a mathematical expression or programming context, or it could just be a term used as a placeholder in prose.

In the paragraph below, the letter "n" is being used as a variable in prose:

<p>If there are <var>n</var> pipes leading to the ice
cream factory then I expect at <em>least</em> <var>n</var>
flavours of ice cream to be available for purchase!</p>

3.12.15. The samp element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.
Otherwise: any inline-level content.
Element-specific attributes:
None, but the title attribute has special semantics on this element when used with the dfn element.
DOM interface:
No difference from HTMLElement.

The samp element represents (sample) output from a program or computing system.

See the pre and kbd elements for more detais.

This example shows the samp element being used inline:

<p>The computer said <samp>Too much cheese in tray
two</samp> but I didn't know what that meant.</p>

This second example shows a block of sample output. Nested samp and kbd elements allow for the styling of specific elements of the sample output using a style sheet.

<pre><samp><samp class="prompt">jdoe@mowmow:~$</samp> <kbd>ssh demo.example.com</kbd>
Last login: Tue Apr 12 09:10:17 2005 from mowmow.example.com on pts/1
Linux demo 2.6.10-grsec+gg3+e+fhs6b+nfs+gr0501+++p3+c4a+gr2b-reslog-v6.189 #1 SMP Tue Feb 1 11:22:36 PST 2005 i686 unknown

<samp class="prompt">jdoe@demo:~$</samp> <samp class="cursor">_</samp></samp></pre>

3.12.16. The kbd element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The kbd element represents user input (typically keyboard input, although it may also be used to represent other input, such as voice commands).

When the kbd element is nested inside a samp element, it represents the input as it was echoed by the system.

When the kbd element contains a samp element, it represents input based on system output, for example invoking a menu item.

When the kbd element is nested inside another kbd element, it represents an actual key or other single unit of input as appropriate for the input mechanism.

Here the kbd element is used to indicate keys to press:

<p>To make George eat an apple, press <kbd><kbd>Shift</kbd>+<kbd>F3</kbd></kbd></p>

In this second example, the user is told to pick a particular menu item. The outer kbd element marks up a block of input, with the inner kbd elements representing each individual step of the input, and the samp elements inside them indicating that the steps are input based on something being displayed by the system, in this case menu labels:

<p>To make George eat an apple, select
    <kbd><kbd><samp>File</samp></kbd>|<kbd><samp>Eat Apple...</samp></kbd></kbd>
</p>

3.12.17. The sup and sub elements

Strictly inline-level content.

Contexts in which these elements may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The sup element represents a superscript and the sub element represents a subscript.

These elements must only be used to mark up typographical conventions with specific meanings, not for typographical presentation for presentation's sake. For example, it would be inappropriate for the sup and sub elements to be used in the name of the LaTeX document preparation system. In general, authors should not use these elements if the absence of those elements would not change the meaning of the content.

When the sub element is used inside a var element, it represents the subscript that identifies the variable in a family of variables.

<p>The coordinate of the <var>i</var>th point is
(<var>x<sub><var>i</var></sub></var>, <var>y<sub><var>i</var></sub></var>).
For example, the 10th point has coordinate
(<var>x<sub>10</sub></var>, <var>y<sub>10</sub></var>).</p>

In certain languages, superscripts are part of the typographical conventions for some abbreviations.

<p>The most beautiful women are
<span lang="fr"><abbr>M<sup>lle</sup></abbr> Gwendoline</span> and 
<span lang="fr"><abbr>M<sup>me</sup></abbr> Denise</span>.</p>

Mathematical expressions often use subscripts and superscripts.

<var>E</var>=<var>m</var><var>c</var><sup>2</sup>
f(<var>x</var>, <var>n</var>) = log<sub>4</sub><var>x</var><sup><var>n</var></sup>

3.12.18. The span element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
When used in an element whose content model is only strictly inline-level content: only strictly inline-level content.
Otherwise: any inline-level content.
Element-specific attributes:
None, but the title attribute has special semantics on this element when used with the dfn element.
DOM interface:
No difference from HTMLElement.

The span element doesn't mean anything on its own, but can be useful when used together with other attributes, e.g. class, lang, or dir, or when used in conjunction with the dfn element.

3.12.19. The i element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None, but the title attribute has special semantics on this element when used with the dfn element.
DOM interface:
No difference from HTMLElement.

The i element represents a span of text in an alternate voice or mood, or otherwise offset from the normal prose, such as a taxonomic designation, a technical term, an idiomatic phrase from another language, a thought, a ship name, or some other prose whose typical typographic presentation is italicized.

Terms in languages different from the main text should be annotated with lang attributes (xml:lang in XML).

The examples below show uses of the i element:

<p>The <i>felis silvestris catus</i> is cute.</p>
<p>The <i>block-level elements</i> are defined above.</p>
<p>There is a certain <i lang="fr">je ne sais quoi</i> in the air.</p>

In the following example, a dream sequence is marked up using i elements.

<p>Raymond tried to sleep.</p>
<p><i>The ship sailed away on Thursday</i>, he
dreamt. <i>The ship had many people aboard, including a beautiful
princess called Carey. He watched her, day-in, day-out, hoping she
would notice him, but she never did.</i></p>
<p><i>Finally one night he picked up the courage to speak with
her—</i></p>
<p>Raymond woke with a start as the fire alarm rang out.</p>

The i element should be used as a last resort when no other element is more appropriate. In particular, citations should use the cite element, defining instances of terms should use the dfn element, stress emphasis should use the em element, importance should be denoted with the strong element, quotes should be marked up with the q element, and small print should use the small element.

Style sheets can be used to format i elements, just like any other element can be restyled. Thus, it is not the case that content in i elements will necessarily be italicised.

3.12.20. The b element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The b element represents a span of text to be stylistically offset from the normal prose without conveying any extra importance, such as key words in a document abstract, product names in a review, or other spans of text whose typical typographic presentation is boldened.

The following example shows a use of the b element to highlight key words without marking them up as important:

<p>The <b>frobonitor</b> and <b>barbinator</b> components are fried.</p>

The following would be incorrect usage:

<p><b>WARNING!</b> Do not frob the barbinator!</p>

In the previous example, the correct element to use would have been strong, not b.

In the following example, objects in a text adventure are highlighted as being special by use of the b element.

<p>You enter a small room. Your <b>sword</b> glows
brighter. A <b>rat</b> scurries past the corner wall.</p>

The b element should be used as a last resort when no other element is more appropriate. In particular, headers should use the h1 to h6 elements, stress emphasis should use the em element, importance should be denoted with the strong element, and text marked or highlighted should use the m element.

Style sheets can be used to format b elements, just like any other element can be restyled. Thus, it is not the case that content in b elements will necessarily be boldened.

3.12.21. The bdo element

Strictly inline-level content.

Contexts in which this element may be used:
Where strictly inline-level content is allowed.
Content model:
Strictly inline-level content.
Element-specific attributes:
None, but the dir global attribute is required on this element.
DOM interface:
No difference from HTMLElement.

The bdo element allows authors to override the Unicode bidi algorithm by explicitly specifying a direction override. [BIDI]

Authors must specify the dir attribute on this element, with the value ltr to specify a left-to-right override and with the value rtl to specify a right-to-left override.

If the element has the dir attribute set to the exact value ltr, then for the purposes of the bidi algorithm, the user agent must act as if there was a U+202D LEFT-TO-RIGHT OVERRIDE character at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at the end of the element.

If the element has the dir attribute set to the exact value rtl, then for the purposes of the bidi algorithm, the user agent must act as if there was a U+202E RIGHT-TO-LEFT OVERRIDE character at the start of the element, and a U+202C POP DIRECTIONAL FORMATTING at the end of the element.

The requirements on handling the bdo element for the bidi algorithm may be implemented indirectly through the style layer. For example, an HTML+CSS user agent should implement these requirements by implementing the CSS unicode-bidi property. [CSS21]

3.13. Edits

The ins and del elements represent edits to the document.

3.13.1. The ins element

Transparent block-level element, and transparent strictly inline-level content.

Contexts in which this element may be used:
Where block-level elements is expected.
Where strictly inline-level content is allowed.
Content model:
Transparent.
Element-specific attributes:
cite
datetime
DOM interface:
Uses the HTMLModElement interface.

The ins element represents an addition to the document.

The ins element must be used only where block-level elements or strictly inline-level content can be used.

An ins element can only contain content that would still be conformant if all elements with transparent content models were replaced by their contents.

The following would be syntactically legal:

<aside>
 <ins>
  <p>...</p>
 </ins>
</aside>

As would this:

<aside>
 <ins>
  <em>...</em>
 </ins>
</aside>

However, this last example would be illegal, as em and p cannot both be used inside an aside element at the same time:

<aside>
 <ins>
  <p>...</p>
 </ins>
 <ins>
  <em>...</em>
 </ins>
</aside>

3.13.2. The del element

Block-level element, and strictly inline-level content.

Contexts in which this element may be used:
Where block-level elements is expected.
Where strictly inline-level content is allowed.
Content model:
When the element has a parent: same content model as the parent element (without taking into account the other children of the parent element).
Otherwise: zero or more block-level elements, or inline-level content (but not both).
Element-specific attributes:
cite
datetime
DOM interface:
Uses the HTMLModElement interface.

The del element represents a removal from the document.

The del element must only contain content that would be allowed inside the parent element (regardless of what the parent element actually contains).

The following would be syntactically legal:

<aside>
 <del>
  <p>...</p>
 </del>
 <ins>
  <em>...</em>
 </ins>
</aside>

...even though the p and em elements would never be allowed side by side in the aside element. This is allowed because the del element represents content that was removed, and it is quite possible that an edit could cause an element to go from being an inline-level container to a block-level container, or vice-versa.

3.13.3. Attributes common to ins and del elements

The cite attribute may be used to specify a URI that explains the change. When that document is long, for instance the minutes of a meeting, authors are encouraged to include a fragment identifier pointing to the specific part of that document that discusses the change.

If the cite attribute is present, it must be a URI (or IRI) that explains the change. User agents should allow users to follow such citation links.

The datetime attribute may be used to specify the time and date of the change.

If present, the datetime attribute must be a valid datetime value.

User agents must parse the datetime attribute according to the parse a string as a datetime value algorithm. If that doesn't return a time, then the modification has no associated timestamp (the value is non-conforming; it is not a valid datetime). Otherwise, the modification is marked as having been made at the given datetime. User agents should use the associated timezone information to determine which timezone to present the given datetime in.

The ins and del elements must implement the HTMLModElement interface:

interface HTMLModElement : HTMLElement {
           attribute DOMString cite;
           attribute DOMString dateTime;
};

The cite DOM attribute must reflect the element's >cite content attribute. The dateTime DOM attribute must reflect the element's datetime content attribute.

3.14. Embedded content

3.14.1. The figure element

Block-level element.

Contexts in which this element may be used:
Where block-level elements are expected.
Content model:
In any order, exactly one legend element, and exactly one embedded content element.
Element-specific attributes:
None.
DOM interface:
No difference from HTMLElement.

The figure element represents a paragraph consisting of embedded content and a caption.

The first embedded content element child of the figure element, if any, is the paragraph's content.

The first legend element child of the element, if any, represents the caption of the embedded content. If there is no child legend element, then there is no caption.

If the embedded content cannot be used, then, for the purposes of establishing what the figure element represents:

If the embedded content's fallback content is a single embedded content element
The figure element must be treated as if that embedded content element was the figure element's embedded content. (If that embedded content can't be used either, then this processing must be done again, with the new embedded content's fallback content.)
If the embedded content's fallback is nothing
The entire figure element (including the caption, if any) must be ignored.
If the embedded content's fallback is inline-level content
The entire figure element (including the caption, if any) must be treated as being a single paragraph with that inline-level content as its content.
Otherwise
The entire figure element (including the caption, if any) must be treated as being replaced by that fallback content.

3.14.2. The img element

Strictly inline-level embedded content.

Contexts in which this element may be used:
As the only embedded content child of a figure element.
Where strictly inline-level content is allowed.
Content model:
Empty.
Element-specific attributes:
alt (required)
src (required)
usemap
ismap (but only if one of the ancestor elements is an a element)
height
width
DOM interface:
interface HTMLImageElement : HTMLElement {
           attribute DOMString alt;
           attribute DOMString src;
           attribute DOMString useMap;
           attribute boolean isMap;
           attribute long height;
           attribute long width;
  readonly attribute boolean complete;
};

An instance of HTMLImageElement can be obtained using the Image constructor.

The img element represents a piece of text with an alternate graphical representation. The text is given by the alt attribute, which must be present, and the URI to the graphical representation of that text is given in the src attribute, which must also be present.

The image given by the src attribute is the embedded content, and the value of the alt attribute is the img element's fallback content.

When the alt attribute's value is the empty string, the image supplements the surrounding content. In such cases, the image could be omitted without affecting the meaning of the document.

If the alt attribute is omitted, user agents must treat the element as if it had an alt attribute set to the empty string.

The alt attribute does not represent advisory information. User agents must not present the contents of the alt attribute in the same way as content of the title attribute.

Guidelines on writing "alt" text here.

The src attribute must contain a URI (or IRI). If the src attribute is omitted, there is no alternative image representation.

When the src attribute is set, the user agent must immediately begin to download the specified resource, unless the user agent cannot support images, or its support for images has been disabled.

The download of the image must delay the load event.

Once the download has completed, if the image is a valid image, the user agent must fire a load event on the img element. If the download fails or it completes but the image is not a valid or supported image, the user agent must fire an error event on the img element.

The remote server's response metadata (e.g. an HTTP 404 status code, or associated Content-Type headers) must be ignored when determining whether the resource obtained is a valid image or not.

This allows servers to return images with error responses.

User agents must not support non-image resources with the img element.

The usemap attribute, if present, can indicate that the image has an associated image map.

The ismap attribute, when used on an element that is a descendant of an a element with an href attribute, indicates by its presence that the element provides access to a server-side image map. This affects how events are handled on the corresponding a element.

The ismap attribute is a boolean attribute. The attribute must not be specified on an element that does not have an ancestor a element.

The height and width attributes give the preferred rendered dimensions of the image if the image is to be shown in a visual medium.

Should we require the dimensions to be correct? Should we disallow percentages?

The values of the height and width attributes must be either valid non-negative integers or valid non-negative percentages.

To parse the attributes, user agents must use the rules for parsing dimension values. This will return either an integer length, a percentage value, or nothing. When one of these attributes has no value, it must be ignored.

The user agent requirements for processing the values obtained from parsing these attributes are described in the rendering section.

The img element must be empty.

.

A body element's end tag may be omitted if the body element is not immediately followed by a space character or a comment.

A li element's end tag may be omitted if the li element is immediately followed by another li element or if there is no more content in the parent element.

A dt element's end tag may be omitted if the dt element is immediately followed by another dt element or a dd element.

A dd element's end tag may be omitted if the dd element is immediately followed by another dd element or a dt element, or if there is no more content in the parent element.

A p element's end tag may be omitted if the p element is immediately followed by an address, blockquote, dl, fieldset, form, h1, h2, h3, h4, h5, h6, hr, menu, ol, p, pre, table, or ul element, or if there is no more content in the parent element.

An optgroup element's end tag may be omitted if the optgroup element is immediately followed by another optgroup element, or if there is no more content in the parent element.

An option element's end tag may be omitted if the option element is immediately followed by another option element, or if there is no more content in the parent element.

A colgroup element's start tag may be omitted if the first thing inside the colgroup element is a col element, and if the element is not immediately preceeded by another colgroup element whose end tag has been omitted.

A colgroup element's end tag may be omitted if the colgroup element is not immediately followed by a space character or a comment.

A thead element's end tag may be omitted if the thead element is immediately followed by a tbody or tfoot element.

A tbody element's start tag may be omitted if the first thing inside the tbody element is a tr element, and if the element is not immediately preceeded by a tbody, thead, or tfoot element whose end tag has been omitted.

A tbody element's end tag may be omitted if the tbody element is immediately followed by a tbody or tfoot element, or if there is no more content in the parent element.

A tfoot element's end tag may be omitted if the tfoot element is immediately followed by a tbody element, or if there is no more content in the parent element.

A tr element's end tag may be omitted if the tr element is immediately followed by another tr element, or if there is no more content in the parent element.

A td element's end tag may be omitted if the td element is immediately followed by a td or th element, or if there is no more content in the parent element.

A th element's end tag may be omitted if the th element is immediately followed by a td or th element, or if there is no more content in the parent element.

However, a start tag must never be omitted if it has any attributes.

8.1.2.5. Restrictions on content models

For historical reasons, certain elements have extra restrictions beyond even the restrictions given by their content model.

A p element must not contain blockquote, dl, menu, ol, pre, table, or ul elements, even though these elements are technically allowed inside p elements according to the content models described in this specification. (In fact, if one of those elements is put inside a p element in the markup, it will instead imply a p element end tag before it.)

An optgroup element must not contain optgroup elements, even though these elements are technically allowed to be nested according to the content models described in this specification. (If an optgroup element is put inside another in the markup, it will in fact imply an optgroup end tag before it.)

A table element must not contain tr elements, even though these elements are technically allowed inside table elements according to the content models described in this specification. (If a tr element is put inside a table in the markup, it will in fact imply a tbody start tag before it.)

A single U+000A LINE FEED (LF) character may be placed immediately after the start tag of pre and textarea elements. This does not affect the processing of the element. The otherwise optional U+000A LINE FEED (LF) character must be included if the element's contents start with that character (because otherwise the leading newline in the contents would be treated like the optional newline, and ignored).

The following two pre blocks are equivalent:

<pre>Hello</pre>
<pre>
Hello</pre>
8.1.2.6. Restrictions on the contents of CDATA and RCDATA elements

The text in CDATA and RCDATA elements must not contain any occurences of the string "</" (U+003C LESS-THAN SIGN, U+002F SOLIDUS) followed by characters that case-insensitively match the tag name of the element followed by one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), U+0020 SPACE, U+003E GREATER-THAN SIGN (>), or U+002F SOLIDUS (/), unless that string is part of an escaping text span.

An escaping text span is a span of text (in CDATA and RCDATA elements) and character entity references (in RCDATA elements) that starts with an escaping text span start that is not itself in an escaping text span, and ends at the next escaping text span end.

An escaping text span start is a part of text that consists of the four character sequence "<!--" (U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS).

An escaping text span end is a part of text that consists of the three character sequence "-->" (U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN) whose U+003E GREATER-THAN SIGN (>).

An escaping text span start may share its U+002D HYPHEN-MINUS characters with its corresponding escaping text span end.

The text in CDATA and RCDATA elements must not have an escaping text span start that is not followed by an escaping text span end.

8.1.3. Text

Text is allowed inside elements, attributes, and comments. Text must consist of valid Unicode characters other than U+0000. Text should not contain control characters other than space characters. Extra constraints are placed on what is and what is not allowed in text based on where the text is to be put, as described in the other sections.

8.1.3.1. Newlines

Newlines in HTML may be represented either as U+000D CARRIAGE RETURN (CR) characters, U+000A LINE FEED (LF) characters, or pairs of U+000D CARRIAGE RETURN (CR), U+000A LINE FEED (LF) characters in that order.

8.1.4. Character entity references

In certain cases described in other sections, text may be mixed with character entity references. These can be used to escape characters that couldn't otherwise legally be included in text.

Character entity references must start with a U+0026 AMPERSAND (&). Following this, there are three possible kinds of character entity references:

Named entities
The ampersand must be followed by one of the names given in the entities section, using the same case. The name must be one that is terminated by a U+003B SEMICOLON (;) character.
Decimal numeric entities
The ampersand must be followed by a U+0023 NUMBER SIGN (#) character, followed by one or more digits in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE, representing a base-ten integer that itself is a valid Unicode code point that is not U+0000, U+000D, in the range U+0080 .. U+009F, or in the range 0xD800 .. 0xDFFF (surrogates). The digits must then be followed by a U+003B SEMICOLON character (;).
Hexadecimal numeric entities
The ampersand must be followed by a U+0023 NUMBER SIGN (#) character, which must be followed by either a U+0078 LATIN SMALL LETTER X or a U+0058 LATIN CAPITAL LETTER X character, which must then be followed by one or more digits in the range U+0030 DIGIT ZERO .. U+0039 DIGIT NINE, U+0061 LATIN SMALL LETTER A .. U+0066 LATIN SMALL LETTER F, and U+0041 LATIN CAPITAL LETTER A .. U+0046 LATIN CAPITAL LETTER F, representing a base-sixteen integer that itself is a valid Unicode code point that is not U+0000, U+000D, in the range U+0080 .. U+009F, or in the range 0xD800 .. 0xDFFF (surrogates). The digits must then be followed by a U+003B SEMICOLON character (;).

An ambiguous ampersand is a U+0026 AMPERSAND (&) character that is not the last character in the file, that is not followed by a space character, that is not followed by a start tag that has not been omitted, and that is not followed by another U+0026 AMPERSAND (&) character.

8.1.5. Comments

Comments must start with the four character sequence U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS (<!--). Following this sequence, the comment may have text, with the additional restriction that the text must not contain two consecutive U+002D HYPHEN-MINUS (-) characters, nor end with a U+002D HYPHEN-MINUS (-) character. Finally, the comment must be ended by the three character sequence U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN (-->).

8.2. Parsing HTML documents

This section only applies to user agents, data mining tools, and conformance checkers.

The rules for parsing XML documents (and thus XHTML documents) into DOM trees are covered by the XML and Namespaces in XML specifications, and are out of scope of this specification. [XML] [XMLNS]

For HTML documents, user agents must use the parsing rules described in this section to generate the DOM trees. Together, these rules define what is referred to as the HTML parser.

While the HTML form of HTML5 bears a close resemblance to SGML and XML, it is a separate language with its own parsing rules.

Some earlier versions of HTML (in particular from HTML2 to HTML4) were based on SGML and used SGML parsing rules. However, few (if any) web browsers ever implemented true SGML parsing for HTML documents; the only user agents to strictly handle HTML as an SGML application have historically been validators. The resulting confusion — with validators claiming documents to have one representation while widely deployed Web browsers interoperably implemented a different representation — has wasted decades of productivity. This version of HTML thus returns to a non-SGML basis.

Authors interested in using SGML tools in their authoring pipeline are encouraged to use XML tools and the XML serialisation of HTML5.

This specification defines the parsing rules for HTML documents, whether they are syntactically valid or not. Certain points in the parsing algorithm are said to be parse errors. The error handling for parse errors is well-defined: user agents must either act as described below when encountering such problems, or must abort processing at the first error that they encounter for which they do not wish to apply the rules described below.

Conformance checkers must report at least one parse error condition to the user if one or more parse error conditions exist in the document and must not report parse error conditions if none exist in the document. Conformance checkers may report more than one parse error condition if more than one parse error conditions exist in the document. Conformance checkers are not required to recover from parse errors.

Parse errors are only errors with the syntax of HTML. In addition to checking for parse errors, conformance checkers will also verify that the document obeys all the other conformance requirements described in this specification.

8.2.1. Overview of the parsing model

The input to the HTML parsing process consists of a stream of Unicode characters, which is passed through a tokenisation stage (lexical analysis) followed by a tree construction stage (semantic analysis). The output is a Document object.

Implementations that do not support scripting do not have to actually create a DOM Document object, but the DOM tree in such cases is still used as the model for the rest of the specification.

In the common case, the data handled by the tokenisation stage comes from the network, but it can also come from script, e.g. using the document.write() API.

There is only one set of state for the tokeniser stage and the tree construction stage, but the tree construction stage is reentrant, meaning that while the tree construction stage is handling one token, the tokeniser might be resumed, causing further tokens to be emitted and processed before the first token's processing is complete.

In the following example, the tree construction stage will be called upon to handle a "p" start tag token while handling the "script" start tag token:

...
<script>
 document.write('<p>');
</script>
...

8.2.2. The input stream

The stream of Unicode characters that consists the input to the tokenisation stage will be initially seen by the user agent as a stream of bytes (typically coming over the network or from the local file system). The bytes encode the actual characters according to a particular character encoding, which the user agent must use to decode the bytes into characters.

For XML documents, the algorithm user agents must use to determine the character encoding is given by the XML specification. This section does not apply to XML documents. [XML]

8.2.2.1. Determining the character encoding

In some cases, it might be impractical to unambiguously determine the encoding before parsing the document. Because of this, this specification provides for a two-pass mechanism with an optional pre-scan. Implementations are allowed, as described below, to apply a simplified parsing algorithm to whatever bytes they have available before beginning to parse the document. Then, the real parser is started, using a tentative encoding derived from this pre-parse and other out-of-band metadata. If, while the document is being loaded, the user agent discovers an encoding declaration that conflicts with this information, then the parser can get reinvoked to perform a parse of the document with the real encoding.

User agents must use the following algorithm (the encoding sniffing algorithm) to determine the character encoding to use when decoding a document in the first pass. This algorithm takes as input any out-of-band metadata available to the user agent (e.g. the Content-Type metadata of the document) and all the bytes available so far, and returns an encoding and a confidence. The confidence is either tentative or certain. The encoding used, and whether the confidence in that encoding is tentative or confident, is used during the parsing to determine whether to change the encoding.

  1. If the transport layer specifies an encoding, return that encoding with the confidence certain, and abort these steps.

  2. The user agent may wait for more bytes of the resource to be available, either in this step or at any later step in this algorithm. For instance, a user agent might wait 500ms or 512 bytes, whichever came first. In general preparsing the source to find the encoding improves performance, as it reduces the need to throw away the data structures used when parsing upon finding the encoding information. However, if the user agent delays too long to obtain data to determine the encoding, then the cost of the delay could outweigh any performance improvements from the preparse.

  3. For each of the rows in the following table, starting with the first one and going down, if there are as many or more bytes available than the number of bytes in the first column, and the first bytes of the file match the bytes given in the first column, then return the encoding given in the cell in the second column of that row, with the confidence certain, and abort these steps:

    Bytes in Hexadecimal Description
    FE FF UTF-16BE BOM
    FF FE UTF-16LE BOM
    EF BB BF UTF-8 BOM
  4. Otherwise, the user agent will have to search for explicit character encoding information in the file itself. This should proceed as follows:

    Let position be a pointer to a byte in the input stream, initially pointing at the first byte. If at any point during these substeps the user agent either runs out of bytes or decides that scanning further bytes would not be efficient, then skip to the next step of the overall character encoding detection algorithm. User agents may decide that scanning any bytes is not efficient, in which case these substeps are entirely skipped.

    Now, repeat the following "two" steps until the algorithm aborts (either because user agent aborts, as described above, or because a character encoding is found):

    1. If position points to:

      A sequence of bytes starting with: 0x3C 0x21 0x2D 0x2D (ASCII '<!--')

      Advance the position pointer so that it points at the first 0x3E byte which is preceeded by two 0x2D bytes (i.e. at the end of an ASCII '-->' sequence) and comes after the 0x3C byte that was found. (The two 0x2D bytes can be the same as the those in the '<!--' sequence.)

      A sequence of bytes starting with: 0x3C, 0x4D or 0x6D, 0x45 or 0x65, 0x54 or 0x74, 0x41 or 0x61, and finally one of 0x09, 0x0A, 0x0B, 0x0C, 0x0D, 0x20 (case-insensitive ASCII '<meta' followed by a space)
      1. Advance the position pointer so that it points at the next 0x09, 0x0A, 0x0B, 0x0C, 0x0D, or 0x20 byte (the one in sequence of characters matched above).

      2. Get an attribute and its value. If no attribute was sniffed, then skip this inner set of steps, and jump to the second step in the overall "two step" algorithm.

      3. Examine the attribute's name:

        If it is 'charset'

        If the attribute's value is a supported character encoding, then return the given encoding, with confidence tentative, and abort all these steps. Otherwise, do nothing with this attribute, and continue looking for other attributes.

        If it is 'content'

        The attribute's value is now parsed.

        1. Apply the algorithm for extracting an encoding from a Content-Type, giving the attribute's value as the string to parse.
        2. If an encoding was returned, and it is the name of a supported character encoding, then return that encoding, with the confidence tentative, and abort all these steps.
        3. Otherwise, skip this 'content' attribute and continue on with any other attributes.
        Any other name

        Do nothing with that attribute.

      4. Return to step 1 in these inner steps.

      A sequence of bytes starting with a 0x3C byte (ASCII '<'), optionally a 0x2F byte (ASCII '/'), and finally a byte in the range 0x41-0x5A or 0x61-0x7A (an ASCII letter)
      1. Advance the position pointer so that it points at the next 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII FF), 0x0D (ASCII CR), 0x20 (ASCII space), 0x3E (ASCII '>'), 0x3C (ASCII '<') byte.

      2. If the pointer points to a 0x3C (ASCII '<') byte, then return to the first step in the overall "two step" algorithm.

      3. Repeatedly get an attribute until no further attributes can be found, then jump to the second step in the overall "two step" algorithm.

      A sequence of bytes starting with: 0x3C 0x21 (ASCII '<!')
      A sequence of bytes starting with: 0x3C 0x2F (ASCII '</')
      A sequence of bytes starting with: 0x3C 0x3F (ASCII '<?')

      Advance the position pointer so that it points at the first 0x3E byte (ASCII '>') that comes after the 0x3C byte that was found.

      Any other byte

      Do nothing with that byte.

    2. Move position so it points at the next byte in the input stream, and return to the first step of this "two step" algorithm.

    When the above "two step" algorithm says to get an attribute, it means doing this:

    1. If the byte at position is one of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII FF), 0x0D (ASCII CR), 0x20 (ASCII space), or 0x2F (ASCII '/') then advance position to the next byte and start over.

    2. If the byte at position is 0x3C (ASCII '<'), then move position back to the previous byte, and stop looking for an attribute. There isn't one.

    3. If the byte at position is 0x3E (ASCII '>'), then stop looking for an attribute. There isn't one.

    4. Otherwise, the byte at position is the start of the attribute name. Let attribute name and attribute value be the empty string.

    5. Attribute name: Process the byte at position as follows:

      If it is 0x3D (ASCII '='), and the attribute name is longer than the empty string
      Advance position to the next byte and jump to the step below labelled value.
      If it is 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII FF), 0x0D (ASCII CR), or 0x20 (ASCII space)
      Jump to the step below labelled spaces.
      If it is 0x2F (ASCII '/'), 0x3C (ASCII '<'), or 0x3E (ASCII '>')
      Stop looking for an attribute. The attribute's name is the value of attribute name, its value is the empty string.
      If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')
      Append the Unicode character with codepoint b+0x20 to attribute name (where b is the value of the byte at position).
      Anything else
      Append the Unicode character with the same codepoint as the value of the byte at position) to attribute name. (It doesn't actually matter how bytes outside the ASCII range are handled here, since only ASCII characters can contribute to the detection of a character encoding.)
    6. Advance position to the next byte and return to the previous step.

    7. Spaces. If the byte at position is one of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII FF), 0x0D (ASCII CR), or 0x20 (ASCII space) then advance position to the next byte, then, repeat this step.

    8. If the byte at position is not 0x3D (ASCII '='), stop looking for an attribute. Move position back to the previous byte. The attribute's name is the value of attribute name, its value is the empty string.

    9. Advance position past the 0x3D (ASCII '=') byte.

    10. Value. If the byte at position is one of 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII FF), 0x0D (ASCII CR), or 0x20 (ASCII space) then advance position to the next byte, then, repeat this step.

    11. Process the byte at position as follows:

      If it is 0x22 (ASCII '"') or 0x27 ("'")
      1. Let b be the value of the byte at position.
      2. Advance position to the next byte.
      3. If the value of the byte at position is the value of b, then stop looking for an attribute. The attribute's name is the value of attribute name, and its value is the value of attribute value.
      4. Otherwise, if the value of the byte at position is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z'), then append a Unicode character to attribute value whose codepoint is 0x20 more than the value of the byte at position.
      5. Otherwise, append a Unicode character to attribute value whose codepoint is the same as the value of the byte at position.
      6. Return to the second step in these substeps.
      If it is 0x3C (ASCII '<'), or 0x3E (ASCII '>')
      Stop looking for an attribute. The attribute's name is the value of attribute name, its value is the empty string.
      If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')
      Append the Unicode character with codepoint b+0x20 to attribute value (where b is the value of the byte at position).
      Anything else
      Append the Unicode character with the same codepoint as the value of the byte at position) to attribute value.
    12. Process the byte at position as follows:

      If it is 0x09 (ASCII TAB), 0x0A (ASCII LF), 0x0B (ASCII VT), 0x0C (ASCII FF), 0x0D (ASCII CR), 0x20 (ASCII space), 0x3C (ASCII '<'), or 0x3E (ASCII '>')
      Stop looking for an attribute. The attribute's name is the value of attribute name and its value is the value of attribute value.
      If it is in the range 0x41 (ASCII 'A') to 0x5A (ASCII 'Z')
      Append the Unicode character with codepoint b+0x20 to attribute value (where b is the value of the byte at position).
      Anything else
      Append the Unicode character with the same codepoint as the value of the byte at position) to attribute value.
    13. Advance position to the next byte and return to the previous step.

    For the sake of interoperability, user agents should not use a pre-scan algorithm that returns different results than the one described above. (But, if you do, please at least let us know, so that we can improve this algorithm and benefit everyone...)

  5. If the user agent has information on the likely encoding for this page, e.g. based on the encoding of the page when it was last visited, then return that encoding, with the confidence tentative, and abort these steps.

  6. The user agent may attempt to autodetect the character encoding from applying frequency analysis or other algorithms to the data stream. If autodetection succeeds in determining a character encoding, then return that encoding, with the confidence tentative, and abort these steps. [UNIVCHARDET]

  7. Otherwise, return an implementation-defined or user-specified default character encoding, with the confidence tentative. Due to its use in legacy content, windows-1252 is recommended as a default in predominantly Western demographics. In non-legacy environments, the more comprehensive UTF-8 encoding is recommended instead. Since these encodings can in many cases be distinguished by inspection, a user agent may heuristically decide which to use as a default.

8.2.2.2. Character encoding requirements

User agents must at a minimum support the UTF-8 and Windows-1252 encodings, but may support more.

It is not unusual for Web browsers to support dozens if not upwards of a hundred distinct character encodings.

User agents must support the preferred MIME name of every character encoding they support that has a preferred MIME name, and should support all the IANA-registered aliases. [IANACHARSET]

When a user agent would otherwise use the ISO-8859-1 encoding, it must instead use the Windows-1252 encoding. User agents must not support the CESU-8, UTF-7, BOCU-1 and SCSU encodings. [CESU8] [UTF7] [BOCU1] [SCSU]

Support for UTF-32 is not recommended. This encoding is rarely used, and frequently misimplemented.

8.2.2.3. Preprocessing the input stream

Given an encoding, the bytes in the input stream must be converted to Unicode characters for the tokeniser, as described by the rules for that encoding, except that leading U+FEFF BYTE ORDER MARK characters must not be stripped by the encoding layer.

Bytes or sequences of bytes in the original byte stream that could not be converted to Unicode characters must be converted to U+FFFD REPLACEMENT CHARACTER code points.

One leading U+FEFF BYTE ORDER MARK character must be ignored if any are present.

All U+0000 NULL characters in the input must be replaced by U+FFFD REPLACEMENT CHARACTERs. Any occurrences of such characters is a parse error.

U+000D CARRIAGE RETURN (CR) characters, and U+000A LINE FEED (LF) characters, are treated specially. Any CR characters that are followed by LF characters must be removed, and any CR characters not followed by LF characters must be converted to LF characters. Thus, newlines in HTML DOMs are represented by LF characters, and there are never any CR characters in the input to the tokenisation stage.

The next input character is the first character in the input stream that has not yet been consumed. Initially, the next input character is the first character in the input.

The insertion point is the position (just before a character or just before the end of the input stream) where content inserted using document.write() is actually inserted. The insertion point is relative to the position of the character immediately after it, it is not an absolute offset into the input stream. Initially, the insertion point is uninitialised.

The "EOF" character in the tables below is a conceptual character representing the end of the input stream. If the parser is a script-created parser, then the end of the input stream is reached when an explicit "EOF" character (inserted by the document.close() method) is consumed. Otherwise, the "EOF" character is not a real character in the stream, but rather the lack of any further characters.

8.2.2.4. Changing the encoding while parsing

When the parser requires the user agent to change the encoding, it must follow the following steps. This might happen if the encoding sniffing algorithm described above failed to find an encoding, or if it found an encoding that was not the actual encoding of the file.

  1. If the new encoding is UTF-16, change it to UTF-8.
  2. If the new encoding is identical or equivalent to the encoding that is already being used to interpret the input stream, then set the confidence to confident and abort these steps. This happens when the encoding information found in the file matches what the encoding sniffing algorithm determined to be the encoding, and in the second pass through the parser if the first pass found that the encoding sniffing algorithm described in the earlier section failed to find the right encoding.
  3. If all the bytes up to the last byte converted by the current decoder have the same Unicode interpretations in both the current encoding and the new encoding, and if the user agent supports changing the converter on the fly, then the user agent may change to the new converter for the encoding on the fly. Set the encoding to the new encoding, set the confidence to confident, and abort these steps.
  4. Otherwise, navigate to the document again, with replacement enabled, but this time skip the encoding sniffing algorithm and instead just set the encoding to the new encoding and the confidence to confident. Whenever possible, this should be done without actually contacting the network layer (the bytes should be re-parsed from memory), even if, e.g., the document is marked as not being cacheable.

While the invocation of this algorithm is not a parse error, it is still indicative of non-conforming content.

8.2.3. Tokenisation

Implementations must act as if they used the following state machine to tokenise HTML. The state machine must start in the data state. Most states consume a single character, which may have various side-effects, and either switches the state machine to a new state to reconsume the same character, or switches it to a new state (to consume the next character), or repeats the same state (to consume the next character). Some states have more complicated behaviour and can consume several characters before switching to another state.

The exact behaviour of certain states depends on a content model flag that is set after certain tokens are emitted. The flag has several states: PCDATA, RCDATA, CDATA, and PLAINTEXT. Initially it must be in the PCDATA state. In the RCDATA and CDATA states, a further escape flag is used to control the behaviour of the tokeniser. It is either true or false, and initially must be set to the false state.

The output of the tokenisation step is a series of zero or more of the following tokens: DOCTYPE, start tag, end tag, comment, character, end-of-file. DOCTYPE tokens have a name, a public identifier, a system identifier, and a correctness flag. When a DOCTYPE token is created, its name, public identifier, and system identifier must be marked as missing, and the correctness flag must be set to correct (its other state is incorrect). Start and end tag tokens have a tag name and a list of attributes, each of which has a name and a value. Comment and character tokens have data.

When a token is emitted, it must immediately be handled by the tree construction stage. The tree construction stage can affect the state of the content model flag, and can insert additional characters into the stream. (For example, the script element can result in scripts executing and using the dynamic markup insertion APIs to insert characters into the stream being tokenised.)

When an end tag token is emitted, the content model flag must be switched to the PCDATA state.

When an end tag token is emitted with attributes, that is a parse error.

A permitted slash is a U+002F SOLIDUS character that is immediately followed by a U+003E GREATER-THAN SIGN, if, and only if, the current token being processed is a start tag token whose tag name is one of the following: base, link, meta, hr, br, img, embed, param, area, col, input

Before each step of the tokeniser, the user agent may check to see if either one of the scripts in the list of scripts that will execute as soon as possible or the first script in the list of scripts that will execute asynchronously, has completed loading. If one has, then it must be executed and removed from its list.

The tokeniser state machine is as follows:

Data state

Consume the next input character:

U+0026 AMPERSAND (&)
When the content model flag is set to one of the PCDATA or RCDATA states: switch to the entity data state.
Otherwise: treat it as per the "anything else" entry below.
U+002D HYPHEN-MINUS (-)

If the content model flag is set to either the RCDATA state or the CDATA state, and the escape flag is false, and there are at least three characters before this one in the input stream, and the last four characters in the input stream, including this one, are U+003C LESS-THAN SIGN, U+0021 EXCLAMATION MARK, U+002D HYPHEN-MINUS, and U+002D HYPHEN-MINUS ("<!--"), then set the escape flag to true.

In any case, emit the input character as a character token. Stay in the data state.

U+003C LESS-THAN SIGN (<)
When the content model flag is set to the PCDATA state: switch to the tag open state.
When the content model flag is set to either the RCDATA state or the CDATA state and the escape flag is false: switch to the tag open state.
Otherwise: treat it as per the "anything else" entry below.
U+003E GREATER-THAN SIGN (>)

If the content model flag is set to either the RCDATA state or the CDATA state, and the escape flag is true, and the last three characters in the input stream including this one are U+002D HYPHEN-MINUS, U+002D HYPHEN-MINUS, U+003E GREATER-THAN SIGN ("-->"), set the escape flag to false.

In any case, emit the input character as a character token. Stay in the data state.

EOF
Emit an end-of-file token.
Anything else
Emit the input character as a character token. Stay in the data state.
Entity data state

(This cannot happen if the content model flag is set to the CDATA state.)

Attempt to consume an entity.

If nothing is returned, emit a U+0026 AMPERSAND character token.

Otherwise, emit the character token that was returned.

Finally, switch to the data state.

Tag open state

The behaviour of this state depends on the content model flag.

If the content model flag is set to the RCDATA or CDATA states

Consume the next input character. If it is a U+002F SOLIDUS (/) character, switch to the close tag open state. Otherwise, emit a U+003C LESS-THAN SIGN character token and reconsume the current input character in the data state.

If the content model flag is set to the PCDATA state

Consume the next input character:

U+0021 EXCLAMATION MARK (!)
Switch to the markup declaration open state.
U+002F SOLIDUS (/)
Switch to the close tag open state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Create a new start tag token, set its tag name to the lowercase version of the input character (add 0x0020 to the character's code point), then switch to the tag name state. (Don't emit the token yet; further details will be filled in before it is emitted.)
U+0061 LATIN SMALL LETTER A through to U+007A LATIN SMALL LETTER Z
Create a new start tag token, set its tag name to the input character, then switch to the tag name state. (Don't emit the token yet; further details will be filled in before it is emitted.)
U+003E GREATER-THAN SIGN (>)
Parse error. Emit a U+003C LESS-THAN SIGN character token and a U+003E GREATER-THAN SIGN character token. Switch to the data state.
U+003F QUESTION MARK (?)
Parse error. Switch to the bogus comment state.
Anything else
Parse error. Emit a U+003C LESS-THAN SIGN character token and reconsume the current input character in the data state.
Close tag open state

If the content model flag is set to the RCDATA or CDATA states but no start tag token has ever been emitted by this instance of the tokeniser (fragment case), or, if the content model flag is set to the RCDATA or CDATA states and the next few characters do not match the tag name of the last start tag token emitted (case insensitively), or if they do but they are not immediately followed by one of the following characters:

...then emit a U+003C LESS-THAN SIGN character token, a U+002F SOLIDUS character token, and switch to the data state to process the next input character.

Otherwise, if the content model flag is set to the PCDATA state, or if the next few characters do match that tag name, consume the next input character:

U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Create a new end tag token, set its tag name to the lowercase version of the input character (add 0x0020 to the character's code point), then switch to the tag name state. (Don't emit the token yet; further details will be filled in before it is emitted.)
U+0061 LATIN SMALL LETTER A through to U+007A LATIN SMALL LETTER Z
Create a new end tag token, set its tag name to the input character, then switch to the tag name state. (Don't emit the token yet; further details will be filled in before it is emitted.)
U+003E GREATER-THAN SIGN (>)
Parse error. Switch to the data state.
EOF
Parse error. Emit a U+003C LESS-THAN SIGN character token and a U+002F SOLIDUS character token. Reconsume the EOF character in the data state.
Anything else
Parse error. Switch to the bogus comment state.
Tag name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the before attribute name state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Append the lowercase version of the current input character (add 0x0020 to the character's code point) to the current tag token's tag name. Stay in the tag name state.
EOF
Parse error. Emit the current tag token. Reconsume the EOF character in the data state.
U+002F SOLIDUS (/)
Parse error unless this is a permitted slash. Switch to the before attribute name state.
Anything else
Append the current input character to the current tag token's tag name. Stay in the tag name state.
Before attribute name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before attribute name state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Start a new attribute in the current tag token. Set that attribute's name to the lowercase version of the current input character (add 0x0020 to the character's code point), and its value to the empty string. Switch to the attribute name state.
U+002F SOLIDUS (/)
Parse error unless this is a permitted slash. Stay in the before attribute name state.
EOF
Parse error. Emit the current tag token. Reconsume the EOF character in the data state.
Anything else
Start a new attribute in the current tag token. Set that attribute's name to the current input character, and its value to the empty string. Switch to the attribute name state.
Attribute name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the after attribute name state.
U+003D EQUALS SIGN (=)
Switch to the before attribute value state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Append the lowercase version of the current input character (add 0x0020 to the character's code point) to the current attribute's name. Stay in the attribute name state.
U+002F SOLIDUS (/)
Parse error unless this is a permitted slash. Switch to the before attribute name state.
EOF
Parse error. Emit the current tag token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current attribute's name. Stay in the attribute name state.

When the user agent leaves the attribute name state (and before emitting the tag token, if appropriate), the complete attribute's name must be compared to the other attributes on the same token; if there is already an attribute on the token with the exact same name, then this is a parse error and the new attribute must be dropped, along with the value that gets associated with it (if any).

After attribute name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the after attribute name state.
U+003D EQUALS SIGN (=)
Switch to the before attribute value state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
U+0041 LATIN CAPITAL LETTER A through to U+005A LATIN CAPITAL LETTER Z
Start a new attribute in the current tag token. Set that attribute's name to the lowercase version of the current input character (add 0x0020 to the character's code point), and its value to the empty string. Switch to the attribute name state.
U+002F SOLIDUS (/)
Parse error unless this is a permitted slash. Switch to the before attribute name state.
EOF
Parse error. Emit the current tag token. Reconsume the EOF character in the data state.
Anything else
Start a new attribute in the current tag token. Set that attribute's name to the current input character, and its value to the empty string. Switch to the attribute name state.
Before attribute value state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before attribute value state.
U+0022 QUOTATION MARK (")
Switch to the attribute value (double-quoted) state.
U+0026 AMPERSAND (&)
Switch to the attribute value (unquoted) state and reconsume this input character.
U+0027 APOSTROPHE (')
Switch to the attribute value (single-quoted) state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
EOF
Parse error. Emit the current tag token. Reconsume the character in the data state.
Anything else
Append the current input character to the current attribute's value. Switch to the attribute value (unquoted) state.
Attribute value (double-quoted) state

Consume the next input character:

U+0022 QUOTATION MARK (")
Switch to the before attribute name state.
U+0026 AMPERSAND (&)
Switch to the entity in attribute value state.
EOF
Parse error. Emit the current tag token. Reconsume the character in the data state.
Anything else
Append the current input character to the current attribute's value. Stay in the attribute value (double-quoted) state.
Attribute value (single-quoted) state

Consume the next input character:

U+0027 APOSTROPHE (')
Switch to the before attribute name state.
U+0026 AMPERSAND (&)
Switch to the entity in attribute value state.
EOF
Parse error. Emit the current tag token. Reconsume the character in the data state.
Anything else
Append the current input character to the current attribute's value. Stay in the attribute value (single-quoted) state.
Attribute value (unquoted) state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the before attribute name state.
U+0026 AMPERSAND (&)
Switch to the entity in attribute value state.
U+003E GREATER-THAN SIGN (>)
Emit the current tag token. Switch to the data state.
EOF
Parse error. Emit the current tag token. Reconsume the character in the data state.
Anything else
Append the current input character to the current attribute's value. Stay in the attribute value (unquoted) state.
Entity in attribute value state

Attempt to consume an entity.

If nothing is returned, append a U+0026 AMPERSAND character to the current attribute's value.

Otherwise, append the returned character token to the current attribute's value.

Finally, switch back to the attribute value state that you were in when were switched into this state.

Bogus comment state

(This can only happen if the content model flag is set to the PCDATA state.)

Consume every character up to the first U+003E GREATER-THAN SIGN character (>) or the end of the file (EOF), whichever comes first. Emit a comment token whose data is the concatenation of all the characters starting from and including the character that caused the state machine to switch into the bogus comment state, up to and including the last consumed character before the U+003E character, if any, or up to the end of the file otherwise. (If the comment was started by the end of the file (EOF), the token is empty.)

Switch to the data state.

If the end of the file was reached, reconsume the EOF character.

Markup declaration open state

(This can only happen if the content model flag is set to the PCDATA state.)

If the next two characters are both U+002D HYPHEN-MINUS (-) characters, consume those two characters, create a comment token whose data is the empty string, and switch to the comment start state.

Otherwise if the next seven characters are a case-insensitive match for the word "DOCTYPE", then consume those characters and switch to the DOCTYPE state.

Otherwise, is is a parse error. Switch to the bogus comment state. The next character that is consumed, if any, is the first character that will be in the comment.

Comment start state

Consume the next input character:

U+002D HYPHEN-MINUS (-)
Switch to the comment start dash state.
U+003E GREATER-THAN SIGN (>)
Parse error. Emit the comment token. Switch to the data state.
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Append the input character to the comment token's data. Switch to the comment state.
Comment start dash state

Consume the next input character:

U+002D HYPHEN-MINUS (-)
Switch to the comment end state
U+003E GREATER-THAN SIGN (>)
Parse error. Emit the comment token. Switch to the data state.
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Append a U+002D HYPHEN-MINUS (-) character and the input character to the comment token's data. Switch to the comment state.
Comment state

Consume the next input character:

U+002D HYPHEN-MINUS (-)
Switch to the comment end dash state
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Append the input character to the comment token's data. Stay in the comment state.
Comment end dash state

Consume the next input character:

U+002D HYPHEN-MINUS (-)
Switch to the comment end state
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Append a U+002D HYPHEN-MINUS (-) character and the input character to the comment token's data. Switch to the comment state.
Comment end state

Consume the next input character:

U+003E GREATER-THAN SIGN (>)
Emit the comment token. Switch to the data state.
U+002D HYPHEN-MINUS (-)
Parse error. Append a U+002D HYPHEN-MINUS (-) character to the comment token's data. Stay in the comment end state.
EOF
Parse error. Emit the comment token. Reconsume the EOF character in the data state.
Anything else
Parse error. Append two U+002D HYPHEN-MINUS (-) characters and the input character to the comment token's data. Switch to the comment state.
DOCTYPE state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the before DOCTYPE name state.
Anything else
Parse error. Reconsume the current character in the before DOCTYPE name state.
Before DOCTYPE name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before DOCTYPE name state.
U+003E GREATER-THAN SIGN (>)
Parse error. Create a new DOCTYPE token. Set its correctness flag to incorrect. Emit the token. Switch to the data state.
EOF
Parse error. Create a new DOCTYPE token. Set its correctness flag to incorrect. Emit the token. Reconsume the EOF character in the data state.
Anything else
Create a new DOCTYPE token. Set the token's name name to the current input character. Switch to the DOCTYPE name state.
DOCTYPE name state

First, consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Switch to the after DOCTYPE name state.
U+003E GREATER-THAN SIGN (>)
Emit the current DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's name. Stay in the DOCTYPE name state.
After DOCTYPE name state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the after DOCTYPE name state.
U+003E GREATER-THAN SIGN (>)
Emit the current DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else

If the next six characters are a case-insensitive match for the word "PUBLIC", then consume those characters and switch to the before DOCTYPE public identifier state.

Otherwise, if the next six characters are a case-insensitive match for the word "SYSTEM", then consume those characters and switch to the before DOCTYPE system identifier state.

Otherwise, this is the parse error. Switch to the bogus DOCTYPE state.

Before DOCTYPE public identifier state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before DOCTYPE public identifier state.
U+0022 QUOTATION MARK (")
Set the DOCTYPE token's public identifier to the empty string, then switch to the DOCTYPE public identifier (double-quoted) state.
U+0027 APOSTROPHE (')
Set the DOCTYPE token's public identifier to the empty string, then switch to the DOCTYPE public identifier (single-quoted) state.
U+003E GREATER-THAN SIGN (>)
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Parse error. Switch to the bogus DOCTYPE state.
DOCTYPE public identifier (double-quoted) state

Consume the next input character:

U+0022 QUOTATION MARK (")
Switch to the after DOCTYPE public identifier state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's public identifier. Stay in the DOCTYPE public identifier (double-quoted) state.
DOCTYPE public identifier (single-quoted) state

Consume the next input character:

U+0027 APOSTROPHE (')
Switch to the after DOCTYPE public identifier state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's public identifier. Stay in the DOCTYPE public identifier (single-quoted) state.
After DOCTYPE public identifier state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the after DOCTYPE public identifier state.
U+0022 QUOTATION MARK (")
Set the DOCTYPE token's system identifier to the empty string, then switch to the DOCTYPE system identifier (double-quoted) state.
U+0027 APOSTROPHE (')
Set the DOCTYPE token's system identifier to the empty string, then switch to the DOCTYPE system identifier (single-quoted) state.
U+003E GREATER-THAN SIGN (>)
Emit the current DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Parse error. Switch to the bogus DOCTYPE state.
Before DOCTYPE system identifier state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the before DOCTYPE system identifier state.
U+0022 QUOTATION MARK (")
Set the DOCTYPE token's system identifier to the empty string, then switch to the DOCTYPE system identifier (double-quoted) state.
U+0027 APOSTROPHE (')
Set the DOCTYPE token's system identifier to the empty string, then switch to the DOCTYPE system identifier (single-quoted) state.
U+003E GREATER-THAN SIGN (>)
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Parse error. Switch to the bogus DOCTYPE state.
DOCTYPE system identifier (double-quoted) state

Consume the next input character:

U+0022 QUOTATION MARK (")
Switch to the after DOCTYPE system identifier state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's system identifier. Stay in the DOCTYPE system identifier (double-quoted) state.
DOCTYPE system identifier (single-quoted) state

Consume the next input character:

U+0027 APOSTROPHE (')
Switch to the after DOCTYPE system identifier state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Append the current input character to the current DOCTYPE token's system identifier. Stay in the DOCTYPE system identifier (single-quoted) state.
After DOCTYPE system identifier state

Consume the next input character:

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
Stay in the after DOCTYPE system identifier state.
U+003E GREATER-THAN SIGN (>)
Emit the current DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Parse error. Switch to the bogus DOCTYPE state.
Bogus DOCTYPE state

Consume the next input character:

U+003E GREATER-THAN SIGN (>)
Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Switch to the data state.
EOF
Parse error. Set the DOCTYPE token's correctness flag to incorrect. Emit that DOCTYPE token. Reconsume the EOF character in the data state.
Anything else
Stay in the bogus DOCTYPE state.
8.2.3.1. Tokenising entities

This section defines how to consume an entity. This definition is used when parsing entities in text and in attributes.

The behaviour depends on the identity of the next character (the one immediately after the U+0026 AMPERSAND character):

U+0009 CHARACTER TABULATION
U+000A LINE FEED (LF)
U+000B LINE TABULATION
U+000C FORM FEED (FF)
U+0020 SPACE
U+003C LESS-THAN SIGN
U+0026 AMPERSAND
EOF
Not an entity. No characters are consumed, and nothing is returned. (This is not an error, either.)
U+0023 NUMBER SIGN (#)

Consume the U+0023 NUMBER SIGN.

The behaviour further depends on the character after the U+0023 NUMBER SIGN:

U+0078 LATIN SMALL LETTER X
U+0058 LATIN CAPITAL LETTER X

Consume the X.

Follow the steps below, but using the range of characters U+0030 DIGIT ZERO through to U+0039 DIGIT NINE, U+0061 LATIN SMALL LETTER A through to U+0066 LATIN SMALL LETTER F, and U+0041 LATIN CAPITAL LETTER A, through to U+0046 LATIN CAPITAL LETTER F (in other words, 0-9, A-F, a-f).

When it comes to interpreting the number, interpret it as a hexadecimal number.

Anything else

Follow the steps below, but using the range of characters U+0030 DIGIT ZERO through to U+0039 DIGIT NINE (i.e. just 0-9).

When it comes to interpreting the number, interpret it as a decimal number.

Consume as many characters as match the range of characters given above.

If no characters match the range, then don't consume any characters (and unconsume the U+0023 NUMBER SIGN character and, if appropriate, the X character). This is a parse error; nothing is returned.

Otherwise, if the next character is a U+003B SEMICOLON, consume that too. If it isn't, there is a parse error.

If one or more characters match the range, then take them all and interpret the string of characters as a number (either hexadecimal or decimal as appropriate).

If that number is one of the numbers in the first column of the following table, then this is a parse error. Find the row with that number in the first column, and return a character token for the Unicode character given in the second column of that row.

Number Unicode character
0x0D U+000A LINE FEED (LF)
0x80 U+20AC EURO SIGN ('€')
0x81 U+FFFD REPLACEMENT CHARACTER
0x82 U+201A SINGLE LOW-9 QUOTATION MARK ('‚')
0x83 U+0192 LATIN SMALL LETTER F WITH HOOK ('ƒ')
0x84 U+201E DOUBLE LOW-9 QUOTATION MARK ('„')
0x85 U+2026 HORIZONTAL ELLIPSIS ('…')
0x86 U+2020 DAGGER ('†')
0x87 U+2021 DOUBLE DAGGER ('‡')
0x88 U+02C6 MODIFIER LETTER CIRCUMFLEX ACCENT ('ˆ')
0x89 U+2030 PER MILLE SIGN ('‰')
0x8A U+0160 LATIN CAPITAL LETTER S WITH CARON ('Š')
0x8B U+2039 SINGLE LEFT-POINTING ANGLE QUOTATION MARK ('‹')
0x8C U+0152 LATIN CAPITAL LIGATURE OE ('Œ')
0x8D U+FFFD REPLACEMENT CHARACTER
0x8E U+017D LATIN CAPITAL LETTER Z WITH CARON ('Ž')
0x8F U+FFFD REPLACEMENT CHARACTER
0x90 U+FFFD REPLACEMENT CHARACTER
0x91 U+2018 LEFT SINGLE QUOTATION MARK ('‘')
0x92 U+2019 RIGHT SINGLE QUOTATION MARK ('’')
0x93 U+201C LEFT DOUBLE QUOTATION MARK ('“')
0x94 U+201D RIGHT DOUBLE QUOTATION MARK ('”')
0x95 U+2022 BULLET ('•')
0x96 U+2013 EN DASH ('–')
0x97 U+2014 EM DASH ('—')
0x98 U+02DC SMALL TILDE ('˜')
0x99 U+2122 TRADE MARK SIGN ('™')
0x9A U+0161 LATIN SMALL LETTER S WITH CARON ('š')
0x9B U+203A SINGLE RIGHT-POINTING ANGLE QUOTATION MARK ('›')
0x9C U+0153 LATIN SMALL LIGATURE OE ('œ')
0x9D U+FFFD REPLACEMENT CHARACTER
0x9E U+017E LATIN SMALL LETTER Z WITH CARON ('ž')
0x9F U+0178 LATIN CAPITAL LETTER Y WITH DIAERESIS ('Ÿ')

Otherwise, if the number is zero, if the number is higher than 0x10FFFF, or if it's one of the surrogate characters (characters in the range 0xD800 to 0xDFFF), then this is a parse error; return a character token for the U+FFFD REPLACEMENT CHARACTER character instead.

Otherwise, return a character token for the Unicode character whose code point is that number.

Anything else

Consume the maximum number of characters possible, with the consumed characters case-sensitively matching one of the identifiers in the first column of the entities table.

If no match can be made, then this is a parse error. No characters are consumed, and nothing is returned.

If the last character matched is not a U+003B SEMICOLON (;), there is a parse error.

If the entity is being consumed as part of an attribute, and the last character matched is not a U+003B SEMICOLON (;), and the next character is in the range U+0030 DIGIT ZERO to U+0039 DIGIT NINE, U+0041 LATIN CAPITAL LETTER A to U+005A LATIN CAPITAL LETTER Z, or U+0061 LATIN SMALL LETTER A to U+007A LATIN SMALL LETTER Z, then, for historical reasons, all the characters that were matched after the U+0026 AMPERSAND (&) must be unconsumed, and nothing is returned.

Otherwise, return a character token for the character corresponding to the entity name (as given by the second column of the entities table).

If the markup contains I'm &notit; I tell you, the entity is parsed as "not", as in, I'm ¬it; I tell you. But if the markup was I'm &notin; I tell you, the entity would be parsed as "notin;", resulting in I'm ∉ I tell you.

8.2.4. Tree construction

The input to the tree construction stage is a sequence of tokens from the tokenisation stage. The tree construction stage is associated with a DOM Document object when a parser is created. The "output" of this stage consists of dynamically modifying or extending that document's DOM tree.

Tree construction passes through several phases. Initially, UAs must act according to the steps described as being those of the initial phase.

This specification does not define when an interactive user agent has to render the Document available to the user, or when it has to begin accepting user input.

When the steps below require the UA to append a character to a node, the UA must collect it and all subsequent consecutive characters that would be appended to that node, and insert one Text node whose data is the concatenation of all those characters.

DOM mutation events must not fire for changes caused by the UA parsing the document. (Conceptually, the parser is not mutating the DOM, it is constructing it.) This includes the parsing of any content inserted using document.write() and document.writeln() calls. [DOM3EVENTS]

Not all of the tag names mentioned below are conformant tag names in this specification; many are included to handle legacy content. They still form part of the algorithm that implementations are required to implement to claim conformance.

The algorithm described below places no limit on the depth of the DOM tree generated, or on the length of tag names, attribute names, attribute values, text nodes, etc. While implementators are encouraged to avoid arbitrary limits, it is recognised that practical concerns will likely force user agents to impose nesting depths.

8.2.4.1. The initial phase

Initially, the tree construction stage must handle each token emitted from the tokenisation stage as follows:

A character token that is one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE

Ignore the token.

A comment token

Append a Comment node to the Document object with the data attribute set to the data given in the comment token.

A DOCTYPE token

If the DOCTYPE token's name does not case-insensitively match the string "HTML", or if the token's public identifier is not missing, or if the token's system identifier is not missing, then there is a parse error. Conformance checkers may, instead of reporting this error, switch to a conformance checking mode for another language (e.g. based on the DOCTYPE token a conformance checker could recognise that the document is an HTML4-era document, and defer to an HTML4 conformance checker.)

Append a DocumentType node to the Document node, with the name attribute set to the name given in the DOCTYPE token; the publicId attribute set to the public identifier given in the DOCTYPE token, or the empty string if the public identifier was not set; the systemId attribute set to the system identifier given in the DOCTYPE token, or the empty string if the system identifier was not set; and the other attributes specific to DocumentType objects set to null and empty lists as appropriate. Associate the DocumentType node with the Document object so that it is returned as the value of the doctype attribute of the Document object.

Then, if the DOCTYPE token matches one of the conditions in the following list, then set the document to quirks mode:

Otherwise, if the DOCTYPE token matches one of the conditions in the following list, then set the document to limited quirks mode:

The name, system identifier, and public identifier strings must be compared to the values given in the lists above in a case-insensitive manner.

Then, switch to the root element phase of the tree construction stage.

A start tag token
An end tag token
A character token that is not one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE
An end-of-file token

Parse error.

Set the document to quirks mode.

Then, switch to the root element phase of the tree construction stage and reprocess the current token.

8.2.4.2. The root element phase

After the initial phase, as each token is emitted from the tokenisation stage, it must be processed as described in this section.

A DOCTYPE token

Parse error. Ignore the token.

A comment token

Append a Comment node to the Document object with the data attribute set to the data given in the comment token.

A character token that is one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE

Ignore the token.

A character token that is not one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE
A start tag token
An end tag token
An end-of-file token

Create an HTMLElement node with the tag name html, in the HTML namespace. Append it to the Document object. Switch to the main phase and reprocess the current token.

Should probably make end tags be ignored, so that "</head><!-- --><html>" puts the comment before the root node (or should we?)

The root element can end up being removed from the Document object, e.g. by scripts; nothing in particular happens in such cases, content continues being appended to the nodes as described in the next section.

8.2.4.3. The main phase

After the root element phase, each token emitted from the tokenisation stage must be processed as described in this section. This is by far the most involved part of parsing an HTML document.

The tree construction stage in this phase has several pieces of state: a stack of open elements, a list of active formatting elements, a head element pointer, a form element pointer, and an insertion mode.

We could just fold insertion modes and phases into one concept (and duplicate the two rules common to all insertion modes into all of them).

8.2.4.3.1. The stack of open elements

Initially the stack of open elements contains just the html root element node created in the last phase before switching to this phase (or, in the fragment case, the html element created as part of that algorithm). That's the topmost node of the stack. It never gets popped off the stack. (This stack grows downwards.)

The current node is the bottommost node in this stack.

Elements in the stack fall into the following categories:

Special

The following HTML elements have varying levels of special parsing rules: address, area, base, basefont, bgsound, blockquote, body, br, center, col, colgroup, dd, dir, div, dl, dt, embed, fieldset, form, frame, frameset, h1, h2, h3, h4, h5, h6, head, hr, iframe, image, img, input, isindex, li, link, listing, menu, meta, noembed, noframes, noscript, ol, optgroup, option, p, param, plaintext, pre, script, select, spacer, style, tbody, textarea, tfoot, thead, title, tr, ul, and wbr.

Scoping

The following HTML elements introduce new scopes for various parts of the parsing: button, caption, html, marquee, object, table, td and th.

Formatting

The following HTML elements are those that end up in the list of active formatting elements: a, b, big, em, font, i, nobr, s, small, strike, strong, tt, and u.

Phrasing

All other elements found while parsing an HTML document.

Still need to add these new elements to the lists: event-source, section, nav, article, aside, header, footer, datagrid, command

The stack of open elements is said to have an element in scope or have an element in table scope when the following algorithm terminates in a match state:

  1. Initialise node to be the current node (the bottommost node of the stack).

  2. If node is the target node, terminate in a match state.

  3. Otherwise, if node is a table element, terminate in a failure state.

  4. Otherwise, if the algorithm is the "has an element in scope" variant (rather than the "has an element in table scope" variant), and node is one of the following, terminate in a failure state:

  5. Otherwise, if node is an html element, terminate in a failure state. (This can only happen if the node is the topmost node of the stack of open elements, and prevents the next step from being invoked if there are no more elements in the stack.)

  6. Otherwise, set node to the previous entry in the stack of open elements and return to step 2. (This will never fail, since the loop will always terminate in the previous step if the top of the stack is reached.)

Nothing happens if at any time any of the elements in the stack of open elements are moved to a new location in, or removed from, the Document tree. In particular, the stack is not changed in this situation. This can cause, amongst other strange effects, content to be appended to nodes that are no longer in the DOM.

In some cases (namely, when closing misnested formatting elements), the stack is manipulated in a random-access fashion.

8.2.4.3.2. The list of active formatting elements

Initially the list of active formatting elements is empty. It is used to handle mis-nested formatting element tags.

The list contains elements in the formatting category, and scope markers. The scope markers are inserted when entering buttons, object elements, marquees, table cells, and table captions, and are used to prevent formatting from "leaking" into tables, buttons, object elements, and marquees.

When the steps below require the UA to reconstruct the active formatting elements, the UA must perform the following steps:

  1. If there are no entries in the list of active formatting elements, then there is nothing to reconstruct; stop this algorithm.
  2. If the last (most recently added) entry in the list of active formatting elements is a marker, or if it is an element that is in the stack of open elements, then there is nothing to reconstruct; stop this algorithm.
  3. Let entry be the last (most recently added) element in the list of active formatting elements.
  4. If there are no entries before entry in the list of active formatting elements, then jump to step 8.
  5. Let entry be the entry one earlier than entry in the list of active formatting elements.
  6. If entry is neither a marker nor an element that is also in the stack of open elements, go to step 4.
  7. Let entry be the element one later than entry in the list of active formatting elements.
  8. Perform a shallow clone of the element entry to obtain clone. [DOM3CORE]
  9. Append clone to the current node and push it onto the stack of open elements so that it is the new current node.
  10. Replace the entry for entry in the list with an entry for clone.
  11. If the entry for clone in the list of active formatting elements is not the last entry in the list, return to step 7.

This has the effect of reopening all the formatting elements that were opened in the current body, cell, or caption (whichever is youngest) that haven't been explicitly closed.

The way this specification is written, the list of active formatting elements always consists of elements in chronological order with the least recently added element first and the most recently added element last (except for while steps 8 to 11 of the above algorithm are being executed, of course).

When the steps below require the UA to clear the list of active formatting elements up to the last marker, the UA must perform the following steps:

  1. Let entry be the last (most recently added) entry in the list of active formatting elements.
  2. Remove entry from the list of active formatting elements.
  3. If entry was a marker, then stop the algorithm at this point. The list has been cleared up to the last marker.
  4. Go to step 1.
8.2.4.3.3. Creating and inserting HTML elements

When the steps below require the UA to create an element for a token, the UA must create a node implementing the interface appropriate for the element type corresponding to the tag name of the token (as given in the section of this specification that defines that element, e.g. for an a element it would be the HTMLAnchorElement interface), with the tag name being the name of that element, with the node being in the HTML namespace, and with the attributes on the node being those given in the given token.

When the steps below require the UA to insert an HTML element for a token, the UA must first create an element for the token, and then append this node to the current node, and push it onto the stack of open elements so that it is the new current node.

The steps below may also require that the UA insert an HTML element in a particular place, in which case the UA must create an element for the token and then insert or append the new node in the location specified. (This happens in particular during the parsing of tables with invalid content.)

The interface appropriate for an element that is not defined in this specification is HTMLElement.

The generic CDATA parsing algorithm and the generic RCDATA parsing algorithm consist of the following steps. These algorithms are always invoked in response to a start tag token, and are always passed a context node, typically the current node, which is used as the place to insert the resulting element node.

  1. Create an element for the token.

  2. Append the new element to the given context node.

  3. If the algorithm that was invoked is the generic CDATA parsing algorithm, switch the tokeniser's content model flag to the CDATA state; otherwise the algorithm invoked was the generic RCDATA parsing algorithm, switch the tokeniser's content model flag to the RCDATA state.

  4. Then, collect all the character tokens that the tokeniser returns until it returns a token that is not a character token, or until it stops tokenising.

  5. If this process resulted in a collection of character tokens, append a single Text node, whose contents is the concatenation of all those tokens' characters, to the new element node.

  6. The tokeniser's content model flag will have switched back to the PCDATA state.

  7. If the next token is an end tag token with the same tag name as the start tag token, ignore it. Otherwise, this is a parse error.

8.2.4.3.4. Closing elements that have implied end tags

When the steps below require the UA to generate implied end tags, then, if the current node is a dd element, a dt element, an li element, a p element, a tbody element, a td element, a tfoot element, a th element, a thead element, a tr element, the UA must act as if an end tag with the respective tag name had been seen and then generate implied end tags again.

The step that requires the UA to generate implied end tags but lists an element to exclude from the process, then the UA must perform the above steps as if that element was not in the above list.

8.2.4.3.5. The element pointers

Initially the head element pointer and the form element pointer are both null.

Once a head element has been parsed (whether implicitly or explicitly) the head element pointer gets set to point to this node.

The form element pointer points to the last form element that was opened and whose end tag has not yet been seen. It is used to make form controls associate with forms in the face of dramatically bad markup, for historical reasons.

8.2.4.3.6. The insertion mode

Initially the insertion mode is "before head". It can change to "in head", "in head noscript", "after head", "in body", "in table", "in caption", "in column group", "in table body", "in row", "in cell", "in select", "after body", "in frameset", and "after frameset" during the course of the parsing, as described below. It affects how certain tokens are processed.

If the tree construction stage is switched from the main phase to the trailing end phase and back again, the various pieces of state are not reset; the UA must act as if the state was maintained.

When the steps below require the UA to reset the insertion mode appropriately, it means the UA must follow these steps:

  1. Let last be false.
  2. Let node be the last node in the stack of open elements.
  3. If node is the first node in the stack of open elements, then set last to true. If the context element of the HTML fragment parsing algorithm is neither a td element nor a th element, then set node to the context element. (fragment case)
  4. If node is a select element, then switch the insertion mode to "in select" and abort these steps. (fragment case)
  5. If node is a td or th element, then switch the insertion mode to "in cell" and abort these steps.
  6. If node is a tr element, then switch the insertion mode to "in row" and abort these steps.
  7. If node is a tbody, thead, or tfoot element, then switch the insertion mode to "in table body" and abort these steps.
  8. If node is a caption element, then switch the insertion mode to "in caption" and abort these steps.
  9. If node is a colgroup element, then switch the insertion mode to "in column group" and abort these steps. (fragment case)
  10. If node is a table element, then switch the insertion mode to "in table" and abort these steps.
  11. If node is a head element, then switch the insertion mode to "in body" ("in body"! not "in head"!) and abort these steps. (fragment case)
  12. If node is a body element, then switch the insertion mode to "in body" and abort these steps.
  13. If node is a frameset element, then switch the insertion mode to "in frameset" and abort these steps. (fragment case)
  14. If node is an html element, then: if the head element pointer is null, switch the insertion mode to "before head", otherwise, switch the insertion mode to "after head". In either case, abort these steps. (fragment case)
  15. If last is true, then set the insertion mode to "in body" and abort these steps. (fragment case)
  16. Let node now be the node before node in the stack of open elements.
  17. Return to step 3.
8.2.4.3.7. How to handle tokens in the main phase

Tokens in the main phase must be handled as follows:

A DOCTYPE token

Parse error. Ignore the token.

A start tag whose tag name is "html"

If this start tag token was not the first start tag token, then it is a parse error.

For each attribute on the token, check to see if the attribute is already present on the top element of the stack of open elements. If it is not, add the attribute and its corresponding value to that element.

An end-of-file token

Generate implied end tags.

If there are more than two nodes on the stack of open elements, or if there are two nodes but the second node is not a body node, this is a parse error.

Otherwise, if the parser was originally created as part of the HTML fragment parsing algorithm, and there's more than one element in the stack of open elements, and the second node on the stack of open elements is not a body node, then this is a parse error. (fragment case)

Stop parsing.

This fails because it doesn't imply HEAD and BODY tags. We should probably expand out the insertion modes and merge them with phases and then put the three things here into each insertion mode instead of trying to factor them out so carefully.

Anything else

Depends on the insertion mode:

If the insertion mode is "before head"

Handle the token as follows:

A character token that is one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE

Append the character to the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A start tag whose tag name is "head"

Create an element for the token.

Set the head element pointer to this new element node.

Append the new element to the current node and push it onto the stack of open elements.

Change the insertion mode to "in head".

A start tag token whose tag name is one of: "base", "link", "meta", "script", "style", "title"

Act as if a start tag token with the tag name "head" and no attributes had been seen, then reprocess the current token.

This will result in a head element being generated, and with the current token being reprocessed in the "in head" insertion mode.

An end tag whose tag name is one of: "head", "body", "html", "p", "br"

Act as if a start tag token with the tag name "head" and no attributes had been seen, then reprocess the current token.

Any other end tag

Parse error. Ignore the token.

Do we really want to ignore end tags here?

A character token that is not one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE
Any other start tag token

Act as if a start tag token with the tag name "head" and no attributes had been seen, then reprocess the current token.

This will result in an empty head element being generated, with the current token being reprocessed in the "after head" insertion mode.

If the insertion mode is "in head"

Handle the token as follows.

A character token that is one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE

Append the character to the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A start tag whose tag name is one of: "base", "link"

Insert an HTML element for the token.

A start tag whose tag name is "meta"

Insert an HTML element for the token.

If the element has a charset attribute, and its value is a supported encoding, and the confidence is currently tentative, then change the encoding to the encoding given by the value of the charset attribute.

Otherwise, if the element has a content attribute, and applying the algorithm to extract an encoding from a Content-Type to its value returns a supported encoding encoding, and the confidence is currently tentative, then change the encoding to the encoding encoding.

A start tag whose tag name is "title"

Follow the generic RCDATA parsing algorithm, with the head element pointer as the context node, unless that's null, in which case use the current node (fragment cose).

A start tag whose tag name is "noscript", if scripting is enabled:
A start tag whose tag name is "style"

Follow the generic CDATA parsing algorithm, with the current node as the context node.

A start tag whose tag name is "noscript", if scripting is disabled:

Insert a noscript element for the token.

Change the insertion mode to "in head noscript".

A start tag whose tag name is "script"

Create an element for the token.

Mark the element as being "parser-inserted". This ensures that, if the script is external, any document.write() calls in the script will execute in-line, instead of blowing the document away, as would happen in most other cases.

Switch the tokeniser's content model flag to the CDATA state.

Then, collect all the character tokens that the tokeniser returns until it returns a token that is not a character token, or until it stops tokenising.

If this process resulted in a collection of character tokens, append a single Text node to the script element node whose contents is the concatenation of all those tokens' characters.

The tokeniser's content model flag will have switched back to the PCDATA state.

If the next token is not an end tag token with the tag name "script", then this is a parse error; mark the script element as "already executed". Otherwise, the token is the script element's end tag, so ignore it.

If the parser was originally created for the HTML fragment parsing algorithm, then mark the script element as "already executed", and skip the rest of the processing described for this token (including the part below where "scripts that will execute as soon as the parser resumes" are executed). (fragment case)

Marking the script element as "already executed" prevents it from executing when it is inserted into the document a few paragraphs below. Thus, scripts missing their end tags and scripts that were inserted using innerHTML aren't executed.

Let the old insertion point have the same value as the current insertion point. Let the insertion point be just before the next input character.

Append the new element to the current node. Special processing occurs when a script element is inserted into a document that might cause some script to execute, which might cause new characters to be inserted into the tokeniser.

Let the insertion point have the value of the old insertion point. (In other words, restore the insertion point to the value it had before the previous paragraph. This value might be the "undefined" value.)

At this stage, if there is a script that will execute as soon as the parser resumes, then:

If the tree construction stage is being called reentrantly, say from a call to document.write():

Abort the processing of any nested invokations of the tokeniser, yielding control back to the caller. (Tokenisation will resume when the caller returns to the "outer" tree construction stage.)

Otherwise:

Follow these steps:

  1. Let the script be the script that will execute as soon as the parser resumes. There is no longer a script that will execute as soon as the parser resumes.

  2. Pause until the script has completed loading.

  3. Let the insertion point be just before the next input character.

  4. Execute the script.

  5. Let the insertion point be undefined again.

  6. If there is once again a script that will execute as soon as the parser resumes, then repeat these steps from step 1.

An end tag whose tag name is "head"

Pop the current node (which will be the head element) off the stack of open elements.

Change the insertion mode to "after head".

An end tag whose tag name is one of: "body", "html", "p", "br"

Act as described in the "anything else" entry below.

A start tag whose tag name is "head"
Any other end tag

Parse error. Ignore the token.

Anything else

Act as if an end tag token with the tag name "head" had been seen, and reprocess the current token.

In certain UAs, some elements don't trigger the "in body" mode straight away, but instead get put into the head. Do we want to copy that?

If the insertion mode is "in head noscript"
An end tag whose tag name is "noscript"

Pop the current node (which will be a noscript element) from the stack of open elements; the new current node will be a head element.

Switch the insertion mode to "in head".

A character token that is one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE
A comment token
A start tag whose tag name is one of: "link", "meta", "style"

Process the token as if the insertion mode had been "in head".

An end tag whose tag name is one of: "p", "br"

Act as described in the "anything else" entry below.

A start tag whose tag name is one of: "head", "noscript"
Any other end tag

Parse error. Ignore the token.

Anything else

Parse error. Act as if an end tag with the tag name "noscript" had been seen and reprocess the current token.

If the insertion mode is "after head"

Handle the token as follows:

A character token that is one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE

Append the character to the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A start tag whose tag name is "body"

Insert a body element for the token.

Change the insertion mode to "in body".

A start tag whose tag name is "frameset"

Insert a frameset element for the token.

Change the insertion mode to "in frameset".

A start tag token whose tag name is one of: "base", "link", "meta", "script", "style", "title"

Parse error.

Push the node pointed to by the head element pointer onto the stack of open elements.

Process the token as if the insertion mode had been "in head".

Pop the current node (which will be the node pointed to by the head element pointer) off the stack of open elements.

Anything else

Act as if a start tag token with the tag name "body" and no attributes had been seen, and then reprocess the current token.

If the insertion mode is "in body"

Handle the token as follows:

A character token

Reconstruct the active formatting elements, if any.

Append the token's character to the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A start tag token whose tag name is one of: "base", "link", "meta", "script", "style"

Process the token as if the insertion mode had been "in head".

A start tag whose tag name is "title"

Parse error. Process the token as if the insertion mode had been "in head".

A start tag whose tag name is "body"

Parse error.

If the second element on the stack of open elements is not a body element, or, if the stack of open elements has only one node on it, then ignore the token. (fragment case)

Otherwise, for each attribute on the token, check to see if the attribute is already present on the body element (the second element) on the stack of open elements. If it is not, add the attribute and its corresponding value to that element.

An end tag whose tag name is "body"

If the second element in the stack of open elements is not a body element, this is a parse error. Ignore the token. (fragment case)

Otherwise, if there is a node in the stack of open elements that is not either a dd element, a dt element, an li element, a p element, a tbody element, a td element, a tfoot element, a th element, a thead element, a tr element, the body element, or the html element, then this is a parse error.

Change the insertion mode to "after body".

An end tag whose tag name is "html"

Act as if an end tag with tag name "body" had been seen, then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

A start tag whose tag name is one of: "address", "blockquote", "center", "dir", "div", "dl", "fieldset", "listing", "menu", "ol", "p", "ul"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Insert an HTML element for the token.

A start tag whose tag name is "pre"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Insert an HTML element for the token.

If the next token is a U+000A LINE FEED (LF) character token, then ignore that token and move on to the next one. (Newlines at the start of pre blocks are ignored as an authoring convenience.)

A start tag whose tag name is "form"

If the form element pointer is not null, ignore the token with a parse error.

Otherwise:

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Insert an HTML element for the token, and set the form element pointer to point to the element created.

A start tag whose tag name is "li"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Run the following algorithm:

  1. Initialise node to be the current node (the bottommost node of the stack).

  2. If node is an li element, then pop all the nodes from the current node up to node, including node, then stop this algorithm. If more than one node is popped, then this is a parse error.

  3. If node is not in the formatting category, and is not in the phrasing category, and is not an address or div element, then stop this algorithm.

  4. Otherwise, set node to the previous entry in the stack of open elements and return to step 2.

Finally, insert an li element.

A start tag whose tag name is one of: "dd", "dt"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Run the following algorithm:

  1. Initialise node to be the current node (the bottommost node of the stack).

  2. If node is a dd or dt element, then pop all the nodes from the current node up to node, including node, then stop this algorithm. If more than one node is popped, then this is a parse error.

  3. If node is not in the formatting category, and is not in the phrasing category, and is not an address or div element, then stop this algorithm.

  4. Otherwise, set node to the previous entry in the stack of open elements and return to step 2.

Finally, insert an HTML element with the same tag name as the token's.

A start tag whose tag name is "plaintext"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Insert an HTML element for the token.

Switch the content model flag to the PLAINTEXT state.

Once a start tag with the tag name "plaintext" has been seen, that will be the last token ever seen other than character tokens (and the end-of-file token), because there is no way to switch the content model flag out of the PLAINTEXT state.

An end tag whose tag name is one of: "address", "blockquote", "center", "dir", "div", "dl", "fieldset", "listing", "menu", "ol", "pre", "ul"

If the stack of open elements has an element in scope with the same tag name as that of the token, then generate implied end tags.

Now, if the current node is not an element with the same tag name as that of the token, then this is a parse error.

If the stack of open elements has an element in scope with the same tag name as that of the token, then pop elements from this stack until an element with that tag name has been popped from the stack.

An end tag whose tag name is "form"

If the stack of open elements has an element in scope with the same tag name as that of the token, then generate implied end tags.

Now, if the current node is not an element with the same tag name as that of the token, then this is a parse error.

Otherwise, if the current node is an element with the same tag name as that of the token pop that element from the stack.

In any case, set the form element pointer to null.

An end tag whose tag name is "p"

If the stack of open elements has a p element in scope, then generate implied end tags, except for p elements.

If the current node is not a p element, then this is a parse error.

If the stack of open elements has a p element in scope, then pop elements from this stack until the stack no longer has a p element in scope.

Otherwise, act as if a start tag with the tag name p had been seen, then reprocess the current token.

An end tag whose tag name is one of: "dd", "dt", "li"

If the stack of open elements has an element in scope whose tag name matches the tag name of the token, then generate implied end tags, except for elements with the same tag name as the token.

If the current node is not an element with the same tag name as the token, then this is a parse error.

If the stack of open elements has an element in scope whose tag name matches the tag name of the token, then pop elements from this stack until an element with that tag name has been popped from the stack.

A start tag whose tag name is one of: "h1", "h2", "h3", "h4", "h5", "h6"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Insert an HTML element for the token.

An end tag whose tag name is one of: "h1", "h2", "h3", "h4", "h5", "h6"

If the stack of open elements has in scope an element whose tag name is one of "h1", "h2", "h3", "h4", "h5", or "h6", then generate implied end tags.

Now, if the current node is not an element with the same tag name as that of the token, then this is a parse error.

If the stack of open elements has in scope an element whose tag name is one of "h1", "h2", "h3", "h4", "h5", or "h6", then pop elements from the stack until an element with one of those tag names has been popped from the stack.

A start tag whose tag name is "a"

If the list of active formatting elements contains an element whose tag name is "a" between the end of the list and the last marker on the list (or the start of the list if there is no marker on the list), then this is a parse error; act as if an end tag with the tag name "a" had been seen, then remove that element from the list of active formatting elements and the stack of open elements if the end tag didn't already remove it (it might not have if the element is not in table scope).

In the non-conforming stream <a href="a">a<table><a href="b">b</table>x, the first a element would be closed upon seeing the second one, and the "x" character would be inside a link to "b", not to "a". This is despite the fact that the outer a element is not in table scope (meaning that a regular </a> end tag at the start of the table wouldn't close the outer a element).

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token. Add that element to the list of active formatting elements.

A start tag whose tag name is one of: "b", "big", "em", "font", "i", "s", "small", "strike", "strong", "tt", "u"

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token. Add that element to the list of active formatting elements.

A start tag whose tag name is "nobr"

Reconstruct the active formatting elements, if any.

If the stack of open elements has a nobr element in scope, then this is a parse error. Act as if an end tag with the tag name nobr had been seen, then once again reconstruct the active formatting elements, if any.

Insert an HTML element for the token. Add that element to the list of active formatting elements.

An end tag whose tag name is one of: "a", "b", "big", "em", "font", "i", "nobr", "s", "small", "strike", "strong", "tt", "u"

Follow these steps:

  1. Let the formatting element be the last element in the list of active formatting elements that:

    • is between the end of the list and the last scope marker in the list, if any, or the start of the list otherwise, and
    • has the same tag name as the token.

    If there is no such node, or, if that node is also in the stack of open elements but the element is not in scope, then this is a parse error. Abort these steps. The token is ignored.

    Otherwise, if there is such a node, but that node is not in the stack of open elements, then this is a parse error; remove the element from the list, and abort these steps.

    Otherwise, there is a formatting element and that element is in the stack and is in scope. If the element is not the current node, this is a parse error. In any case, proceed with the algorithm as written in the following steps.

  2. Let the furthest block be the topmost node in the stack of open elements that is lower in the stack than the formatting element, and is not an element in the phrasing or formatting categories. There might not be one.

  3. If there is no furthest block, then the UA must skip the subsequent steps and instead just pop all the nodes from the bottom of the stack of open elements, from the current node up to and including the formatting element, and remove the formatting element from the list of active formatting elements.

  4. Let the common ancestor be the element immediately above the formatting element in the stack of open elements.

  5. If the furthest block has a parent node, then remove the furthest block from its parent node.

  6. Let a bookmark note the position of the formatting element in the list of active formatting elements relative to the elements on either side of it in the list.

  7. Let node and last node be the furthest block. Follow these steps:

    1. Let node be the element immediately prior to node in the stack of open elements.
    2. If node is not in the list of active formatting elements, then remove node from the stack of open elements and then go back to step 1.
    3. Otherwise, if node is the formatting element, then go to the next step in the overall algorithm.
    4. Otherwise, if last node is the furthest block, then move the aforementioned bookmark to be immediately after the node in the list of active formatting elements.
    5. If node has any children, perform a shallow clone of node, replace the entry for node in the list of active formatting elements with an entry for the clone, replace the entry for node in the stack of open elements with an entry for the clone, and let node be the clone.
    6. Insert last node into node, first removing it from its previous parent node if any.
    7. Let last node be node.
    8. Return to step 1 of this inner set of steps.
  8. Insert whatever last node ended up being in the previous step into the common ancestor node, first removing it from its previous parent node if any.

  9. Perform a shallow clone of the formatting element.

  10. Take all of the child nodes of the furthest block and append them to the clone created in the last step.

  11. Append that clone to the furthest block.

  12. Remove the formatting element from the list of active formatting elements, and insert the clone into the list of active formatting elements at the position of the aforementioned bookmark.

  13. Remove the formatting element from the stack of open elements, and insert the clone into the stack of open elements immediately after (i.e. in a more deeply nested position than) the position of the furthest block in that stack.

  14. Jump back to step 1 in this series of steps.

The way these steps are defined, only elements in the formatting category ever get cloned by this algorithm.

Because of the way this algorithm causes elements to change parents, it has been dubbed the "adoption agency algorithm" (in contrast with other possibly algorithms for dealing with misnested content, which included the "incest algorithm", the "secret affair algorithm", and the "Heisenberg algorithm").

A start tag whose tag name is "button"

If the stack of open elements has a button element in scope, then this is a parse error; act as if an end tag with the tag name "button" had been seen, then reprocess the token.

Otherwise:

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

Insert a marker at the end of the list of active formatting elements.

A start tag token whose tag name is one of: "marquee", "object"

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

Insert a marker at the end of the list of active formatting elements.

An end tag token whose tag name is one of: "button", "marquee", "object"

If the stack of open elements has in scope an element whose tag name is the same as the tag name of the token, then generate implied end tags.

Now, if the current node is not an element with the same tag name as the token, then this is a parse error.

Now, if the stack of open elements has an element in scope whose tag name matches the tag name of the token, then pop elements from the stack until that element has been popped from the stack, and clear the list of active formatting elements up to the last marker.

A start tag whose tag name is "xmp"

Reconstruct the active formatting elements, if any.

Follow the generic CDATA parsing algorithm, with the current node as the context node.

A start tag whose tag name is "table"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Insert an HTML element for the token.

Change the insertion mode to "in table".

A start tag whose tag name is one of: "area", "basefont", "bgsound", "br", "embed", "img", "param", "spacer", "wbr"

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

A start tag whose tag name is "hr"

If the stack of open elements has a p element in scope, then act as if an end tag with the tag name p had been seen.

Insert an HTML element for the token. Immediately pop the current node off the stack of open elements.

A start tag whose tag name is "image"

Parse error. Change the token's tag name to "img" and reprocess it. (Don't ask.)

A start tag whose tag name is "input"

Reconstruct the active formatting elements, if any.

Insert an input element for the token.

If the form element pointer is not null, then associate the input element with the form element pointed to by the form element pointer.

Pop that input element off the stack of open elements.

A start tag whose tag name is "isindex"

Parse error.

If the form element pointer is not null, then ignore the token.

Otherwise:

Act as if a start tag token with the tag name "form" had been seen.

If the token has an attribute called "action", set the action attribute on the resulting form element to the value of the "action" attribute of the token.

Act as if a start tag token with the tag name "hr" had been seen.

Act as if a start tag token with the tag name "p" had been seen.

Act as if a start tag token with the tag name "label" had been seen.

Act as if a stream of character tokens had been seen (see below for what they should say).

Act as if a start tag token with the tag name "input" had been seen, with all the attributes from the "isindex" token except "name", "action", and "prompt". Set the name attribute of the resulting input element to the value "isindex".

Act as if a stream of character tokens had been seen (see below for what they should say).

Act as if an end tag token with the tag name "label" had been seen.

Act as if an end tag token with the tag name "p" had been seen.

Act as if a start tag token with the tag name "hr" had been seen.

Act as if an end tag token with the tag name "form" had been seen.

If the token has an attribute with the name "prompt", then the first stream of characters must be the same string as given in that attribute, and the second stream of characters must be empty. Otherwise, the two streams of character tokens together should, together with the input element, express the equivalent of "This is a searchable index. Insert your search keywords here: (input field)" in the user's preferred language.

Then need to specify that if the form submission causes just a single form control, whose name is "isindex", to be submitted, then we submit just the value part, not the "isindex=" part.

A start tag whose tag name is "textarea"

Create an element for the token.

If the form element pointer is not null, then associate the textarea element with the form element pointed to by the form element pointer.

Append the new element to the current node.

Switch the tokeniser's content model flag to the RCDATA state.

If the next token is a U+000A LINE FEED (LF) character token, then ignore that token and move on to the next one. (Newlines at the start of textarea elements are ignored as an authoring convenience.)

Then, collect all the character tokens that the tokeniser returns until it returns a token that is not a character token, or until it stops tokenising.

If this process resulted in a collection of character tokens, append a single Text node, whose contents is the concatenation of all those tokens' characters, to the new element node.

The tokeniser's content model flag will have switched back to the PCDATA state.

If the next token is an end tag token with the tag name "textarea", ignore it. Otherwise, this is a parse error.

A start tag whose tag name is one of: "iframe", "noembed", "noframes"
A start tag whose tag name is "noscript", if scripting is enabled:

Follow the generic CDATA parsing algorithm, with the current node as the context node.

A start tag whose tag name is "select"

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

Change the insertion mode to "in select".

An end tag whose tag name is "br"

Parse error. Act as if a start tag token with the tag name "br" had been seen. Ignore the end tag token.

A start or end tag whose tag name is one of: "caption", "col", "colgroup", "frame", "frameset", "head", "option", "optgroup", "tbody", "td", "tfoot", "th", "thead", "tr"
An end tag whose tag name is one of: "area", "basefont", "bgsound", "br", "embed", "hr", "iframe", "image", "img", "input", "isindex", "noembed", "noframes", "param", "select", "spacer", "table", "textarea", "wbr"
An end tag whose tag name is "noscript", if scripting is enabled:

Parse error. Ignore the token.

A start or end tag whose tag name is one of: "event-source", "section", "nav", "article", "aside", "header", "footer", "datagrid", "command"

Work in progress!

A start tag token not covered by the previous entries

Reconstruct the active formatting elements, if any.

Insert an HTML element for the token.

This element will be a phrasing element.

An end tag token not covered by the previous entries

Run the following algorithm:

  1. Initialise node to be the current node (the bottommost node of the stack).

  2. If node has the same tag name as the end tag token, then:

    1. Generate implied end tags.

    2. If the tag name of the end tag token does not match the tag name of the current node, this is a parse error.

    3. Pop all the nodes from the current node up to node, including node, then stop this algorithm.

  3. Otherwise, if node is in neither the formatting category nor the phrasing category, then this is a parse error. Stop this algorithm. The end tag token is ignored.

  4. Set node to the previous entry in the stack of open elements.

  5. Return to step 2.

If the insertion mode is "in table"
A character token that is one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE

Append the character to the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A start tag whose tag name is "caption"

Clear the stack back to a table context. (See below.)

Insert a marker at the end of the list of active formatting elements.

Insert an HTML element for the token, then switch the insertion mode to "in caption".

A start tag whose tag name is "colgroup"

Clear the stack back to a table context. (See below.)

Insert an HTML element for the token, then switch the insertion mode to "in column group".

A start tag whose tag name is "col"

Act as if a start tag token with the tag name "colgroup" had been seen, then reprocess the current token.

A start tag whose tag name is one of: "tbody", "tfoot", "thead"

Clear the stack back to a table context. (See below.)

Insert an HTML element for the token, then switch the insertion mode to "in table body".

A start tag whose tag name is one of: "td", "th", "tr"

Act as if a start tag token with the tag name "tbody" had been seen, then reprocess the current token.

A start tag whose tag name is "table"

Parse error. Act as if an end tag token with the tag name "table" had been seen, then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

An end tag whose tag name is "table"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token. (fragment case)

Otherwise:

Generate implied end tags.

Now, if the current node is not a table element, then this is a parse error.

Pop elements from this stack until a table element has been popped from the stack.

Reset the insertion mode appropriately.

An end tag whose tag name is one of: "body", "caption", "col", "colgroup", "html", "tbody", "td", "tfoot", "th", "thead", "tr"

Parse error. Ignore the token.

Anything else

Parse error. Process the token as if the insertion mode was "in body", with the following exception:

If the current node is a table, tbody, tfoot, thead, or tr element, then, whenever a node would be inserted into the current node, it must instead be inserted into the foster parent element.

The foster parent element is the parent element of the last table element in the stack of open elements, if there is a table element and it has such a parent element. If there is no table element in the stack of open elements (fragment case), then the foster parent element is the first element in the stack of open elements (the html element). Otherwise, if there is a table element in the stack of open elements, but the last table element in the stack of open elements has no parent, or its parent node is not an element, then the foster parent element is the element before the last table element in the stack of open elements.

If the foster parent element is the parent element of the last table element in the stack of open elements, then the new node must be inserted immediately before the last table element in the stack of open elements in the foster parent element; otherwise, the new node must be appended to the foster parent element.

When the steps above require the UA to clear the stack back to a table context, it means that the UA must, while the current node is not a table element or an html element, pop elements from the stack of open elements. If this causes any elements to be popped from the stack, then this is a parse error.

The current node being an html element after this process is a fragment case.

If the insertion mode is "in caption"
An end tag whose tag name is "caption"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token. (fragment case)

Otherwise:

Generate implied end tags.

Now, if the current node is not a caption element, then this is a parse error.

Pop elements from this stack until a caption element has been popped from the stack.

Clear the list of active formatting elements up to the last marker.

Switch the insertion mode to "in table".

A start tag whose tag name is one of: "caption", "col", "colgroup", "tbody", "td", "tfoot", "th", "thead", "tr"
An end tag whose tag name is "table"

Parse error. Act as if an end tag with the tag name "caption" had been seen, then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

An end tag whose tag name is one of: "body", "col", "colgroup", "html", "tbody", "td", "tfoot", "th", "thead", "tr"

Parse error. Ignore the token.

Anything else

Process the token as if the insertion mode was "in body".

If the insertion mode is "in column group"
A character token that is one of one of U+0009 CHARACTER TABULATION, U+000A LINE FEED (LF), U+000B LINE TABULATION, U+000C FORM FEED (FF), or U+0020 SPACE

Append the character to the current node.

A comment token

Append a Comment node to the current node with the data attribute set to the data given in the comment token.

A start tag whose tag name is "col"

Insert a col element for the token. Immediately pop the current node off the stack of open elements.

An end tag whose tag name is "colgroup"

If the current node is the root html element, then this is a parse error, ignore the token. (fragment case)

Otherwise, pop the current node (which will be a colgroup element) from the stack of open elements. Switch the insertion mode to "in table".

An end tag whose tag name is "col"

Parse error. Ignore the token.

Anything else

Act as if an end tag with the tag name "colgroup" had been seen, and then, if that token wasn't ignored, reprocess the current token.

The fake end tag token here can only be ignored in the fragment case.

If the insertion mode is "in table body"
A start tag whose tag name is "tr"

Clear the stack back to a table body context. (See below.)

Insert a tr element for the token, then switch the insertion mode to "in row".

A start tag whose tag name is one of: "th", "td"

Parse error. Act as if a start tag with the tag name "tr" had been seen, then reprocess the current token.

An end tag whose tag name is one of: "tbody", "tfoot", "thead"

If the stack of open elements does not have an element in table scope with the same tag name as the token, this is a parse error. Ignore the token.

Otherwise:

Clear the stack back to a table body context. (See below.)

Pop the