A section of code that worked for me in July only partly works now. One issue that I've noticed is that \group_begin: ... \DeclareDocumentCommand \test ... ... \group_end: 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. Andrew