A little late with my reply here but I thought I might aswell say this.
The reason I used \w instead of a-z0-9 is that I'm more used to writing regexes for languages where there are many possibilities for the character set in use. Typically \w will respond according to the character set and use the appropriate characters that are defined as alphanumeric, whereas a-z0-9 is always just those 36 characters. Of course this doesn't make much difference in mIRC at this point, it was just a force of habit, however I guess it doesn't hurt to have some future-proofing put in for when Unicode is supported by mIRC.
