Input Validation is a Sure Thing - The Daily WTF
Validating inputs matters. It's also a challenge. Validating that an input is numeric might be easy, but validating an email address is orders of magnitude harder (and technically isn't a regular language and thus can't be parsed by regex, though you can get close). Validating a URL is also a pretty challenging task, since URLs can contain all sorts of surprising information.
Daniel's co-worker, when tasked with validating URLs, looked at the complexity, and came up with a simple, elegant solution, in JavaScript.
