For those wondering, $regsub (Not to be confused with $regsubex) is an older way of doing RegExp substitutions.

older, and also different, since with $regsubex() a lot more work is performed by mIRC in delaying the evaluation of the substitution parm until after replacements have been made. we should use $regsub() when we can and $regsubex() when we must. since the latter's syntax is a bit friendlier, it's often easy to misuse, and we can probably forgive a man for doing so.