Assertions in Regex

Hi team,
Can we use assertion in Regular Expressions search mode?

Like, “Xinex, a.k.a. Xin”, match “Xin” which is started with a space, but doesn’t match the space.

I have tried “(?<=[:sep:])<X”, but it dosn’t work.

The documentation for Xbench regex (which is POSIX Regex plus a couple of sugar syntax features) is found here: Regular Expressions and Microsoft Word Wildcards :: ApSIC Xbench Documentation.

It’s not clear to me which strings you are trying to match. Could you please provide a small list with 3 or 4 examples of matched strings and 3 or 4 examples of not to be matched strings?