David Kastrup <dak(a)gnu.org&gt; writes: >> Debugger entered--Lisp error: (invalid-regexp "Invalid regular expression") >> re-search-forward("\\(?:\\\\label{\\(?1:[^}]*\\)}\\|\\[[^]]*\\<label[[:space:]]*=[[:space:]]*{?\\(?1:[^],}]+\\)}?\\)\\|\\(^\\)[ >> ]*\\\\\\(begin{SaveListing}\\|part\\|chapter\\|section\\|subsection\\|subsubsection\\|paragraph\\|subparagraph\\|addchap\\|addsec\\)\\*?\\(\\[[^]]*\\]\\)?[[{ >> \n\\]\\|\\(^\\)[ ]*\\\\\\(include\\|input\\|subfile\\)[{ >> ]+\\([^} \n]+\\)\\|\\(^\\)[ >> ]*\\(\\\\appendix\\)\\|\\(\\\\glossary\\|\\\\index\\|\\\\nomenclature\\)[[{]" >> nil t) > > It would be my guess that > > ‘\(?NUM: … \)’ > is the "explicitly numbered group" construct. Normal groups get > their number implicitly, based on their position, which can be > inconvenient. This construct allows you to force a particular > group number. There is no particular restriction on the numbering, > e.g., you can have several groups with the same number in which > case the last one to match (i.e., the rightmost match) will win. > Implicitly numbered groups always get the smallest integer larger > than the one of any previous group. > > is the culprit here. At least in the current XEmacs manual > <URL:http://www.xemacs.org/Documentation/21.5/html/lispref_45.html#SEC599> > I can find nothing of the sort. Yes, that's it. Unfortunately, I use that on purpose in `reftex-label-regexps' which is a customizable list of regexps which gets `regexp-opt'ed and starts `reftex-everything-regexp'. By default, it has one entry matching \label{...} and one matching keyval label={...} arguments. RefTeX relies on the first group in `reftex-everything-regexp' capturing the label name (see reftex-parse.el:242). Without the explicitly numbered groups, the regex for \label{...} would be group 1, but the regex for label={...} would already be two. I don't see an easy fix here on my side.