> Actually, it's the underscores!

Found it. Suggested fix attached.

It can be improved: at least one pair of regexp group brackets can be removed, but I didn't dare doing so because I wasn't sure if it would throw some group numbers off by one.

Alan, please, let's work together and remove unnecessary capture groups from the regexps! Even XEmacs regexps support non-capturing brackets, \(?:...\), and they save time, regexp stack space, and reduce the hassle of computing the 'regexp depth' everywhere.