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In response to one of the FAQs, FSF has noted:

It is possible to use the GPL for a manual, but the GNU Free Documentation License (GFDL) is much better for manuals.

The GPL was designed for programs; it contains lots of complex clauses that are crucial for programs, but that would be cumbersome and unnecessary for a book or manual. For instance, anyone publishing the book on paper would have to either include machine-readable “source code” of the book along with each printed copy, or provide a written offer to send the “source code” later.

If I understand this correctly, in the situation where one shares their PDF along with the TeX source files under the GFDL, a recipient can modify the TeX source files to produce a modified PDF and can share the modified PDF without providing the recipient the modified TeX source files. In this crucial sense, the GFDL is different from GPL in that the latter wouldn't allow for a modified end-product to be distributed unless it is accompanied by the distribution of the corresponding modified source files.

Similarly, CC BY-SA licenses also seem to allow the same practice.

In principle, one can simply use GPL licenses for distributing documentation but as alluded to in the quoted text by the FSF, GPL is too "bloated" for the purposes of documentation. Is there a copyleft license specifically pertaining to documentation that also includes the GPL like structure so that one cannot redistribute a modified version of the documentation file without accompanying it with the modified version of the source files used to produce the documentation file?

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  • 2
    Although the question is self-contained I think, for context, this question arose from the short back and forth in the comment section of this answer: opensource.stackexchange.com/a/8146/20741. Linking the question in the comments there as well.
    – Dvij D.C.
    Oct 20 '20 at 11:57
  • Technically, a printed book is a modified version of the documentation file and a photocopy of selected pages of that book is another modified version. If I distribute such a photocopy, would I also be required to include "source files" that can produce exactly those pages? Oct 21 '20 at 15:01
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    @BartvanIngenSchenau Yes, assuming everyone in the chain followed the terms of the license, you would be in possession of the source files. Thus, you should also be required to provide source files to the people to whom you distribute a modified copy of the work (at least if they request it and you should be required to include a copy of the license in the work regardless so that they are aware of their rights that they can ask for the source files, etc.).
    – Dvij D.C.
    Oct 21 '20 at 15:07
  • Do you realize how prohibitively restrictive such a license is. If I were to print (part of) the document and add some hand-written notes to the printout that I then give to someone else, then I would also have to modify an electronic "source document" to include those same notes and provide that alongside the hardcopy I made. If that "source document" is in a format I am not familiar with, or I don't know how to exactly get it to render my handwriting, then I am not allowed to pass on my annotated printout. Oct 22 '20 at 9:34
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    @BartvanIngenSchenau 1. Well, one can make it reasonable by saying that they have to distribute the version of the source files that pertains to the last relevant electronic changes that they did, or the version of the source files that they received (whichever one is the latest). I was not thinking really that one would be redistributing handwritten changes to a documentation file but it's an important case to consider in principle, I agree. 2. I'm not sure what GPLv3 dictates in such a case, do you know? Because it can certainly be used for documentation, in principle.
    – Dvij D.C.
    Oct 22 '20 at 9:46
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I think the basic problem here is that it's the copyleft nature of the GPL that makes it "bloated". You can grant the same rights as the GPL does in a few lines - all the extra words in the GPL are there to "prevent others from denying you these rights or asking you to surrender the rights".

Is there a copyleft license specifically pertaining to documentation that also includes the GPL like structure so that one cannot redistribute a modified version of the documentation file without accompanying it with the modified version of the source files used to produce the documentation file

Yes: the GFDL (note the s1 definitions of transparent and opaque copies, and the s3 and s4j requirements to make transparent copies available to end-users in nearly all cases. What there isn't is a short licence that does that, for very much the same reasons that there isn't a short copyleft licence for code.

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  • Thanks for your answer. I'm a bit confused by 'if any" in the 4J here: "Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission."
    – Dvij D.C.
    Oct 26 '20 at 17:57
  • @DvijD.C. I understand it to mean "if the previous licensor gave a URL whereat one might acquire a transparent version of his/her document, you must preserve it, unless it's really old, or that licensor says you don't have to".
    – MadHatter
    Oct 26 '20 at 21:09
  • OK, but it doesn't explicitly say then that the person who is redistributing the modified document has to include a transparent copy of the modified document, or does it? Apologies for the naive questions, I find the language of the licenses quite unclear.
    – Dvij D.C.
    Oct 26 '20 at 21:14
  • @DvijD.C.no, s3 says that. Note that s4, which deals with modified versions, explicitly applies the requirements of ss 2 and 3 in respect of the modified version.
    – MadHatter
    Oct 26 '20 at 21:16
  • Ah, I see. I thought s3 only applied to printed copies but I think the third paragraph of s3 stands independent of the first paragraph and thus applies to digital copies as well. I think this is still too permissive tho (say, compared to GPLv3) in that it only applies if the distribution exceeds 100 copies. Also, I am not sure how this can actually work in the case of digital copies, it seems quite untraceable to ascertain for someone as to how many digital copies one has distributed (even for the person who is redistributing if they don't use the site analytics). [...]
    – Dvij D.C.
    Oct 26 '20 at 21:30

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