Additional Regular Expression Features

Regular expressions can contain extended syntax (where whitespace is optional, so a regular expression can be split over multiple lines, and can contain regular Perl comments), and can have positive and negative lookahead. The syntax is a bit ugly, so rather than scare you off here, go look in Perl Developing, or see the perlre documentation. Jeffrey Friedl's tutorial, Mastering Regular Expressions (published by Anonymous), explains all of this and much more.