Introduce \stock... dimens

[josephwright]

[josephwright]

Related plan for the l3 backend at https://github.com/latex3/latex3/tree/setpdfpagesize-alt

[josephwright]

looks good, it also means the backend change at latex3/[email protected] can be simplified to drop the is defined test (possibly, depending on timings involved in using expl3 with other formats)

Older-format-newer-expl3 ...

[davidcarlisle]

@josephwright

Older-format-newer-expl3 ... yes sure although that's a temporary change managment, but I was more wondering about other formats, as \stock... is allocated in 2e code, would we keep the defined test long term or drop it (and arrange the registers are allocated in other expl3 wrappers for plain etc (this PR doesn't depend on deciding either way)

[josephwright]

yes sure although that's a temporary change managment, but I was more wondering about other formats, as \stock... is allocated in 2e code, would we keep the defined test long term or drop it (and arrange the registers are allocated in other expl3 wrappers for plain etc (this PR doesn't depend on deciding either way)

The outer test I have is for \@kernel@before@begindocument, so for a 'sufficiently-recent' LaTeX to have the right hook management:

\cs_if_exist:NT \@kernel@before@begindocument
  {
    \tl_gput_right:Nn \@kernel@before@begindocument
      {
        \cs_if_exist:NT \IfDocumentMetadataTF
          {
            \IfDocumentMetadataTF
              {

So the question would be I suspect at what point we decide that 'LaTeX support' assumes that \@kernel@before@begindocument and \IfDocumentMetadataTF exist.