Robert Basic has a new blog post looking at the filtering extension included with most PHP5 distributions.
Filter extension? Maybe it's nothing new for some of you, but it is for me. I've never heard of it before. So I quickly hopped over to PHP.net and the Filter chapter of the manual.
The filter extension (included as of PHP 5.2) helps clean up and validate user input - really any input - like number matching, regular expressions and email addresses. He includes some examples of filtering strings, email and integers as well as ways to sanitize the same strings, ensuring they are valid and clean values.