is necessary to s/unnumbered/appendixsec/ if including the GPLv3 in an Yeah, the discrepancy between the FDL and the GPL seems like a bug. I'll ask about that change.
or if texinfo could support some other subsectioning keyword that works regardless of whether the parent is a main body section or an appendix). It does, and has for many years. @section/@subsection/etc. work in any kind of chapter-level unit. (There is also @raisesections and @lowersections for when an included file is at the "wrong level".) I'll suggest using @section in gpl-3.0.texi. Ditto lgpl-3.0.texi (still not in existence). Also, gpl-2.0.texi adds a @cindex entry, but gpl-3.0.texi lacks it. That means the manual's index is one entry shorter by upgrading to the new license; I'm wondering if that was intentional. I don't know if it's intentional, but the lack of an index entry seems like a good thing to me, so I don't plan to ask about it :). Any desired index entries are better added in the including document, seems to me. Best, Karl