For example, I've GPL software. I'm the author of this GPL software. This GPL software has, between its code, Doxygen comments. These Doxygen comments are written to generate a CC-BY-SA html page, in order to upload this generated documentation in my project website under CC-BY-SA license.
But, is the Doxygen documentation output a "derivate work"? After all, this documentation is based on my GPL source code. In this case, the documentation must be GPL. But, I want the documentation is CC-BY-SA, because it is documentation. GFDL doesn't help. GPL code can't become GFDL (the opposite yes).
If this output is really a derivate work, I think, creates a strange situation, because, if I distribute my work, recipient users can't legally distribute the generated documentation: while with my work I can do I want, the users don't, thus, they have to distribute any derivated work with the same license I offer them.
What is the solution?