It seems to me that neither in the manual nor in the commentary in `gcc.c' it is documented that one can use `@LANGUAGE' to introduce a new `LANGUAGE' to gcc when using custom specs files via `gcc -specs=FILE'. Is it advisible to have the specs syntax's documentation both in the Texinfo manual and as comments in `gcc.c'? Are they kept in sync?
It is also not documented that `#COMMENT' can be used to embed comments. And `\f' (form feed, `^L') could be added to list of white space (in the skip_whitespace function): it's convenient to separate units in hand-made specs files by form feed characters.
specs are an internal format really. It is very subject to change each release. Also some time in the future we might decide to get rid of the specs.
I have a patch to document '#' and '@'. I'll submit it shortly. Currently gcc.c and invoke.texi are mostly kept in sync. However I haven't audited to make sure they are fully in sync. Adding support for \f is probably more complicated than just changing skip_whitespace. I think it is fine to just leave the code as is; users can use multiple blank lines and also comments to separate chunks of spec files.
It looks like the proposed patch from 2007 was never posted. I'm confused, it looks like @language is already documented, while # is documented as causing an error instead of a comment (and it looks like the code tries to do both things with it, which doesn't seem like it would work). I don't know much about spec files, though. :-S