Perl regular expressions man pageThis is the mac-daddy site, but much of it does not apply directly to mIRC's implementation of regular expressions. However, it's as near to the bible of perl regular expressions as you can find online that I know of.
Perl Compatible Regular Expressions (PCRE)mIRC uses an implementation of regex called
PCRE (which has been ported over to the Windows platform) which was written by Philip Hazel and copyrighted by Cambridge University, UK. Currently in version 4.3 (21-May-03), though mIRC uses the version that was out when 6.03 came out which would have been version 3.9.
PHP Manual - LXXXVIII. Regular Expression Functions (Perl-Compatible)Among many other familiar things, PHP uses the PCRE implementation of regular expressions. While these pages are not directly applicable to mIRC as is, they do have lots of good examples and discussion of different regex patterns you might use yourself (or learn from) and use the same implementation of regex as mIRC.
Regular expressions are difficult to start learning, stressful to work with, and can also be great fun to work out (once you've done finally gotten it right). The key is practice, practice and .. oh, did I mention practice?
Basic $regexThis is a class I gave on basic regex. It is intended as only a brief overview of what regex is and what it's not. It starts with what wildcards are ... and what they're not, what they can't do that regex can.