Lookbehind in content regexp

Hi all.

I'm developing a simple zimlet that recognizes telephone numbers in the content of an email and offers the possibility to click to call. To make my life easier, I'd like to use a "lookbehind" regex expression. Since the regex is defined in my zimlet xml file and a lookbehind uses the form "(?<=someconent)", I cannot simply use the "<" char in the expression, since it will invalidate the xml. I tried replacing the "<" with "&lt;" like this "(?&lt;=somecontent)", but then I get an error message "SyntaxError: invalid quantifier" in zimbra webmail as soon as the zimlet gets initialized.

Any ideas?