I spent the past few days learning regualar expressions. I was trying to learn the syntax of any function that accepts a "string pattern". When I searched for that on google, a list of functions was produced that accept "string pattern". I tweaked around with my search for a while until I saw something hinting regular expressions. I saw regular-expressions.info mentioned there, and checked it out. It is very useful and powerful. You can use it in many places as a search. For example, you could search for a valid email address, or a valid domain, or pretty much anything else that has a recognizable pattern.