I don't think
> it needs to be possible to use text from manuals in a program.
> A manual is free if you can publish modified versions as manuals.
And is a text editor free if you can only publish modified versions as
text editors -- not as manuals or tetris games or news-readers or web
browsers?
You have to be free to publish modified versions of the program as
tetris games and news-readers and web browsers, since those are
different programs, but a manual is a different kind of thing
entirely. It is to much to ask that it should be feasible to
conveniently publish a modified version of the program as a manual.
The GPL, for instance, does not permit this in a way that is good
for publication of books on paper.