GNU Free Documentation License.

The license is designed for software documentation and other reference and instructional materials. It stipulates that any copy of the material, even if modified, carry the same license. Those copies may be sold but, if produced in quantity, have to be made available in a format which facilitates further editing. Wikipedia is the largest documentation project to use this license.

Many people and groups, notably the Debian project (based on their Debian Free Software Guidelines), consider the GFDL a non-free license. The reasons for this are that the GFDL allows "invariant" text which cannot be modified or removed, and that its prohibition against digital rights management (DRM) systems affects valid usages as well.

Contents [showhide]
1 Secondary Sections

2 Materials for which commercial redistribution is prohibited

3 Criticisms of the GNU Free Documentation License

3.1 Overly broad DRM clause
3.2 Invariant sections
3.3 GPL incompatible in both directions

4 History

5 Related articles

6 External links

[edit]Secondary Sections
The license explicitly separates any kind of "Document" from "Secondary Sections", which may not be integrated with the Document, but exist as front-matter materials or appendices. Secondary sections can contain information regarding the author's or publisher's relationship to the subject matter, but not any subject matter itself. While the Document itself is wholly editable, and is essentially covered by a license equivalent to (but both-ways incompatible with) the GNU General Public License, some of the secondary sections have various restrictions designed primarily to deal with proper attribution to previous authors.

Specifically, the authors of prior versions have to be acknowledged and certain "invariant sections" specified by the original author and dealing with his or her relationship to the subject matter may not be changed. If the material is modified, its title has to be changed (unless the prior authors give permission to retain the title). The license also has provisions for the handling of front-cover and back-cover texts of books, as well as for "History", "Acknowledgements", "Dedications" and "Endorsements" sections.

[edit]Materials for which commercial redistribution is prohibited
Materials for which commercial redistribution is prohibited generally cannot be used in a GFDL-licensed document, e.g., a Wikipedia article, because the license does not exclude commercial re-use. However in some specific cases, commercial re-uses may be fair use and in that case such materials do not need to be licensed to fall within the GFDL if such fair use is covered by all potential subsequent uses. One good example of such liberal and commercial fair use is parody.

[edit]Criticisms of the GNU Free Documentation License
There are a number of criticisms made about the GNU FDL, with some critics suggesting to authors to use other licenses, such as the Creative Commons license, or even using the GNU GPL.

[edit]Overly broad DRM clause
The GNU FDL contains the following statement.

You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute.
A criticism of this language is that it is too broad, because it applies to private copies made but not distributed. This may be interpreted to mean that you may not be able to legally zip, encrypt, or even save the GNU FDL copies you 'make' in a proprietary file format (to discourage the use of proprietary software?) since they 'obstruct' the reading of the material. As well the term 'technical measures' is also undefined, and thus can be broadly interpreted. Another concern is that some kinds of commercial media or file format may come with built-in DRM features, and one may be forbidden entirely from using such media to distribute the documents, even if you provide alternative means of accessing the source files.

A GNU FDL work can quickly be encumbered because the original title must be kept. This could lead to the situation where there are a whole series of title pages, and dedications, in each and every copy of the book if it has a long lineage. These pages cannot ever be removed, at least not until the work enters the public domain after copyright expires.

The GNU FDL is incompatible in both directions with the GPL, that is GNU FDL material cannot be put into a GPL program, and text from a GNU program cannot be put into the GFDL. Because of this, code samples are often dual-licensed so that they may appear in documentation.

The FDL was released in draft form for feedback in late 1999. After revisions, version 1.1 was issued in March 2000, and version 1.2 in November 2002.