Over at smashing magazine, they have a great post on PHP’s preg_match() regular expressions. They cover a number of advanced topics in light detail, including:
1. Greediness/Laziness
2. Back Referencing
3. Named Groups
4. Word Boundaries
5. Atomic Groups
6. Recursion
7. Callbacks
8. Commenting
http://www.smashingmagazine.com/2009/05/06/introduction-to-advanced-regular-expressions/
The Gahooa Perspective 