Rex eats regular expressions for breakfast. And so can you! This regex tutorial, one of the most detailed on the web, takes you all the way to mastery.

This page explains what makes this site special among all other regex sites, but first let's answer a burning question:

What is the meaning of life?
That's easy. As per the regex humor page, it's simply
^(?=(?!(.)\1)([^\DO:105-93+30])(?-1)(?<!\d(?<=(?![5-90-3])\d))).[^\WHY?]$

Now for the other burning question…

For the people not familiar with challenge sites, a challenge site is mainly a site focussed on offering computer-related problems. Users can register at such a site and start solving challenges. There exist lots of different challenge types.