A section of code that worked for me in July only partly works now. One
issue that I've noticed is that
\DeclareDocumentCommand \test ...
will not in fact create a document command \test -- I get an "Undefined
control sequence" message when I try to use it in the wider document.
The declaration must be outside the group commands -- at least that is
what my experiments tell me. (But \test is recognised within the group
commands.) Is that correct? And is it new? -- I don't recall meeting
this issue back in July.
The xparse documentation doesn't seem to mention this issue and perhaps
should. I can understand the documenters assuming that a document-wide
command would only be defined at the highest level, but in my context
(working with instant preview in LyX) it was quite natural to define it
within the \group_begin:, \group_end: commands of another funtion. I've
changed that now which has resolved at least some of the problem.