Regular expressions are under-valued and most developers tend to only know the basics. Having a thorough understanding of how regular expressions work, will be incredibly helpful when you need to parse structured data.
This presentation will assume you already know what regular expressions are, but will sum up (with an example) some fancy things you probably didn’t know were possible with regular expressions.
If you're interested in a more detailed write-up, I suggest you check out http://www.mullie.eu/regular-expressions-basics/ & http://www.mullie.eu/regular-expressions-advanced/
This presentation is based on the PHP-implementation of PCRE, but nearly all programming languages support the same functionality, albeit sometimes with their own twists.