Hi,
I'll add some considerations which looks needed. This will also be an answer to the 'Anonymous' below, who thinks he or she can hide and insult people without even disturbing him ore herself to register into the community...

Stricly speaking, Perl regex are realy much more powerfull than those described in the wonderfull books you refer to. To understand regex as they are used in perl (but also in other langages & tools) I'd rathere refer to

• Mastering Regular Expressions by Jeffrey E. F. Friedl and Andy Oram

A basic thing that one always see written about regex is that the can not count. Meaning that you must know the maximum number of times the <em>...</em> will be embedded..

While this is true of 'standard' regex, this is not true for Perl regex. By using carefull combination of the /e modifier and of the (?{}) programmatic pattern you can do using regex, everithing a parser will do.

IMHO, using a regex or another approach is a matter of taste, and a careful crafted and optimized regex will be more efficent than a sloppy written rec descent parser.

Just my 5 (euro) cents.

Cheers