l3doc: option about whether to expand @@ when typesetting

[wspr]

After some discussion I think the team is fairly evenly split on whether @@ code should be typeset verbatim or with the module name included.

While we decide on a convention for the LaTeX3 code itself, I think it would be fair to add this as an option to l3doc itself.

[FrankMittelbach]

After thinking this over I'm in favor of implementing this as an option with the default being to print @@.

• for individual packages where you have a single module (which is outside of the kernel probably the default) that seems to be the right approach as it makes the documentation shorter and probably easier to read
• for something like the kernel sources I guess I am still in favor of seeing the source documentation matching closely what would be in expl-code.tex and not having @@ all over the place and changing meaning every few pages of documentation .

[josephwright]

I think overall we should avoid this: it's best if the typeset code is the 'live' version.

[wspr]

I think I agree with Frank — I consider the .sty file to be like the “compiled” version of the code, so it might not necessarily be the most readable. (After all, we’re typesetting the .dtx file, not the .sty file!) I prefer not to copy/paste code from the PDF (because of whitespace formatting) so I don’t see a fundamental need for the typeset code to be the .sty version. (Interesting thought experiment: the \cs_set:Nn commands could hypothetically be transformed into \cs_set:Npn in the dtx→sty process…although nesting would be annoying to deal with.)