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Tips on Using the GNU Free Documentation License

This is a brief explanation of how to place a document under the GNU Free Documentation License. For the GNU software licenses, such as the GNU GPL, we have a separate page.

How does one use the optional features of the FDL?
We have a separate page that discusses how to use the optional features of the FDL.
Where must one put the license notification?
It is sufficient to put the full license notice in the “main” file of your document. For example, with the Emacs Lisp Reference Manual, we have many files included by elisp.texi. We keep the full notification in elisp.texi, and in the other files we simply write:
@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990, 1991, 1992, 1993, 1994, 1999
@c   Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
What do I do with scripts that are needed to render my document properly?
We recommend you release these scripts under the GNU FDL as well. Of course, if these scripts are generally useful for other tasks, it is a good idea to release them separately under the GNU GPL.
Is it required for the document to have invariant sections?
No. It is perfectly acceptable for a document to have no invariant sections.
Should I try to make sure the document has some invariant sections?
Not particularly. If a section's contents ought to be invariant, make it invariant.
Should I try to avoid invariant sections?
Not particularly. If a section's contents ought to be invariant, make it invariant.
When should a section be invariant?
First of all, keep in mind that a section that treats technical material cannot be invariant. Only a secondary section can be invariant, and a technical section is not a secondary section.

If the section is text that you're not allowed to modify, such as a copy of the GNU GPL, then it must be invariant. You can't give permission to modify it if you don't have permission to modify it.

(One consequence is that you cannot use preexisting text which covers technical material if you don't have permission to allow modification of that text.)

When a section discusses the philosophy of free software, it is a good idea to make that section invariant. For instance, when we put the GNU Manifesto in a manual, or when we include a section explaining why free documentation is important, we make that section invariant.


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