Regular Expressions are an essential tool for any developer but they're a source of real terror for many web designers. A Regular Expression is a pattern to match strings of text, using RegExp you can save a lot of time and code lines.
In this video recorded during the Fluent 2012: JavaScript & Beyond conference, and recently made available from O'Reilly Media, Lea Verou gives a step-by-step explanation of some useful examples to help us understand RegExp.