xparse regex argument specifier

[blefloch]

With the addition of \peek_regex_replace_once:nnTF to l3regex in #779, it becomes rather easy to implement an all-encompassing argument type in xparse that would cover various additions that people asked throughout the years (e.g., grabbing any number of + or * tokens, grabbing digits, or whatever). Something like

\NewDocumentCommand { \rating }
  { x{[A-Fa-f]} x{\+*|\-*} }
  { \texttt{#1}\textsuperscript{#2} }
\rating A+++
\rating F-

would print A^{+++} and F^-. Just as for other argument types there could be an argument type X with a default value for when the argument is not found.

[u-fischer]

But I guess that one can't do this in an expandable way, and that writing an expandable version that does something more or less sensible e.g. for such a in the bookmarks would be difficult to impossible? (That doesn't mean that one shouldn't write such commands, only that it should be documented/discussed how argument types behave in different contexts).

[josephwright]

Yes, non-expandable only, but that's no different to trailing-optional or verbatim or whatever.

[eg9]

It would be a very nice addition, indeed. I'd not worry about expandability. Parsing expandably has to use different tools anyway.

[josephwright]

I've merged the expl3 support, so we should be good to go here.

[blefloch]

In which files should new argument types be documented?

[josephwright]

I think new stuff should go into usrguide3, as it will be added to the part of xparse that will move 'finally' across in the near future.

[blefloch]

Where is usrguide3? Probably in some branch somewhere, but I cannot find it.

[FrankMittelbach]

In the latex2e repository (but probably only in master at the moment - not checked) with the next PL there (hopefully in a few of days when @PhelypeOleinik has recovered from thesis stress) it should appear in "develop" there.

[josephwright]

It's in https://github.com/latex3/latex2e/tree/hotfix/gh448, which is as-yet not merged to master or to develop. (Ideally each hotfix should get merged across to develop as well as master, but I suspect we are going to bulk-merge master back to develop.)

[FrankMittelbach]

given that there are always merge conflicts because of the date and version changes (and we seldom have several hotfixes at the same time) doing a bulk merge back to develop when the PL is ready seems more sensible to me.

[blefloch]

Thanks all, I'll wait until all is settled down a bit more before starting on this xparse issue. There is no rush at all.

[josephwright]

I've re-reported at latex3/latex2e#1065 in the 2e format and without the discussion of the underlying expl3 code.