On DevShed today there's a new tutorial loking at an advanced form of a very common need in PHP development - form validation.

Web form processing is one of the most important tasks any website can do to process customer-related information. PHP server side scripting offers a variety of solutions for accepting and processing data inputs from any web form. [...] In this article, we will aim to provide PHP solutions which will validate the most common fields used in website development.

They look at validating several different kinds of input including alphanumerica, numeric, names, email addresses and empty fields.