A number of people have raised issues about the GFDL that pertain to converting documentation into software and vice versa. They call for software and documentation to be a single pool of material with compatible licenses.
That goal goes way beyond what I aimed for when writing our licenses. I wrote the GNU GPL as a license for software, and wrote other licenses for documentation. I did not try to make software licenses cover documentation or vice versa. The needs in these two areas are different, so the licenses are often different--and incompatible. For instance, here is the license we used for most GNU manuals before the GFDL: Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Nobody here would deny that this is a free documentation license. It has the advantage of brevity, but in terms of merging the material into a GPL-covered program, there's no difference between this license and the GFDL. Both are incompatible with the GPL. I designed the GPL to be license for free programs: it provides the necessary freedoms for using programs as programs. If you want to print the same material as a book, you can, but you run into practical inconveniences--for instance, the requirement to distribute machine-readable source code does not fit well with the way books are published. The GPL can be used on documentation files, but it wasn't designed for manuals. Likewise, I designed the GFDL to be a license for free manuals: it provides the necessary freedoms for using manuals as manuals, and tried to attract commercial publishers to publish free manuals (though none was interested in doing so at the time I wrote the GFDL). That job was hard enough; I did not undertake to make it a suitable license for software as well. The goal that people are now proposing is much more ambitious: essentially, to have a single license scheme that covers both software and documentation. The benefit of this would be to combine two separate information commons into a single larger one. This commons would not include all free software, nor all free documentation; TeX and Apache would not be part of it, nor would free manuals published under the simple license above. The change would nonetheless be an advance. It is not a straightforward or easy job, however. To design a license that is good for both free software and free documentation, and that is close enough to today's GPL that it qualifies as a successor version, may or may not be possible. In any case, it will take a lot of thought. I intend to make the effort some day, but first I have to finish GPL version 3, which faces other difficult questions.
