The GNU Free Documentation License (GNU FDL or cutty GFDL) is a copyleft license for free content, designed by the Free Saftware Foondation (FSF) for the GNU project. It is the coonterpairt tae the GNU GPL that gies readers the same richts tae copy, caw aboot an modifee a wark an requires aw copies an affcomes tae be tae haund unner the same license. Copies can be selt commercial an aw, but if duin in lairger quantities (greater nor 100) nor the oreeginal document or soorce code maun be seen on tae the wark's receepient.
The license wis designed for guidals, textbeuks, ither reference an instructional materials, an documentation that aften gangs alang wi GPL saftware. Houaniver, it can be uised for ony text-based wark, regairdless o subject maiter. The lairgest project uisin the license is Wikipedia, a general-purpose encyclopaedia, but the license isna awfu popular amang ither projects.
Audio recordin o the full text o the GNU Free Documentation License.
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Table o contents
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.
Commercial redistribution 
The GFDL requires the ability to "copy and distribute the Document in any medium, either commercially or noncommercially" and therefore is incompatible with material that excludes commercial re-use. Material that restricts commercial re-use is incompatible with the license and cannot be incorporated into the work. However, incorporating such restricted material may be fair use under United States copyright law and does 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.
Criticism of the GFDL 
The Debian project and Nathanael Nerode has raised objection. Debian developers eventually voted to consider works licensed under the GFDL to comply with their Debian Free Software Guidelines provided the invariant section clauses are not used. These critics recommend the use of alternate licenses such as the share-alike Creative Commons licenses or even the GNU GPL. They 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 applies to valid usages, like for "private copies made and not distributed".
Overly broad DRM clause 
The GNU FDL contains the 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 means that a licensee is not allowed to save document copies "made" in a proprietary file format or using encryption.
"This means that you cannot publish them under DRM systems to restrict the possessors of the copies. It isn't supposed to refer to use of encryption or file access control on your own copy. I will talk with our lawyer and see if that sentence needs to be clarified."
As of 2006, the sentence has not yet been clarified.
Invariant sections 
A GNU FDL wark can quickly be encumbered acause a new, different, title maun be giv'n an a list o previous titles maun be kept. This coud lead tae the situation whaur thar are a whol series o title peiges, an dedications, in ilka an e'ery copy o the beuk if it haes a lang lineage. These peiges cannae e'er be remuived, at least nae until the wark haes enter'd the public domein efter copyricht expires.
"The dool o invariant sections, e'er syne the 80s whan we first made the GNU Manifesto an invariant section in the Emacs Manual, wis tae mak sure they coud nae be remuived. Specifically, tae mak sure that distributors o Emacs that awso distribute non-free software coud nae remuive the steitments o wir philosophy, whilka they micht think o doin acause those steitements criticize their actions."
GPL incompatible in both directions 
The GNU FDL is incompatible in both directions with the GPL: that is GNU FDL material cannot be put into GPL code and GPL code cannot be put into a GNU FDL manual. Because of this, code samples are often dual-licensed so that they may appear in documentation and can be incorporated into a free software program.
At the June 22nd and 23rd international GPLv3 conference in Barcelona, Moglen hinted that a future version of the GPL could be made suitable for documentation:
By expressing LGPL as just an additional permission on top of GPL we simplify our licensing landscape drastically. It's like for physics getting rid of a force, right? We just unified electro-weak, ok? The grand unified field theory still escapes us until the document licences too are just additional permissions on top of GPL. I don't know how we'll ever get there, that's gravity, it's really hard.
Burdens when printing 
The GNU FDL requires that licensees, when printing a document covered by the license, must also include "this License, the copyright notices, and the license notice saying this License applies to the Document". This means that if a licensee prints out a copy of an article whose text is covered under the GNU FDL, he or she must also include a copyright notice and a physical printout of the GNU FDL, which is a significantly large document in itself.
Ideological tone 
The license has a preamble, which some critics dislike because of its ideological tone.[citation needit] Because the preamble is part of the license, it must be included (along with the rest of the license's text) with every copy of a licensed document.
Transparent formats 
The definition of a "transparent" format is complicated, and may be difficult to apply. For example, drawings are required to be in a format that allows them to be revised straightforwardly with "some widely available drawing editor." The definition of "widely available" may be difficult to interpret, and may change over time, since, e.g., the open-source Inkscape editor is rapidly maturing, but has not yet reached version 1.0. This section, which was rewritten somewhat between versions 1.1 and 1.2 of the license, uses the terms "widely available" and "proprietary" inconsistently and without defining them. According to a strict interpretation of the license, the references to "generic text editors" could be interpreted as ruling out a format used by an open-source word-processor such as Abiword; according to a loose interpretation, however, Microsoft Word .doc format could qualify as transparent, since a subset of .doc files can be edited perfectly using OpenOffice.org, and the format therefore is not one "that can be read and edited only by proprietary word processors."
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. The current state of the license is version 1.2.
The new draft of the GNU FDL includes a number of improvements, such as new terms crafted during the GPLv3 process to improve internationalization, clarifications to help people applying the license to audio and video, and relaxed requirements for using an excerpt from a work.
The new proposed GNU Simpler Free Documentation License has no requirements to maintain Cover Texts and Invariant Sections. This will provide a simpler licensing option for authors who do not wish to use these features in the GNU FDL.
Other free content licenses 
Some of these were developed independently of the GNU FDL, while others were developed in response to perceived flaws in the GNU FDL.
- Creative Commons licenses
- Design Science License
- Free Art license
- Open Content License
- Open Publication License
See also 
- BSD license
- Free software license
- Open content
- Software licensing
- Non-commercial educational
- GFDL official text
- The GNU Free Documentation License
- Free Software and Free Manuals
- Draft of Debian position statement about the GFDL
- Why You Shouldn't Use the GNU FDL
- Why Wikivoyage isn't GFDL: Problems with using the GFDL for short printed texts
- The Free Universal Encyclopedia And Learning Resource
- Guide to the new drafts of documentation licenses