In a new tutorial on PHPBuilder.com today Marc Plotz looks at a handy feature you can use to help improve the security of your PHP application - and it comes included with your PHP5 installation: the filter extension.

Validation is perhaps the most important thing you can do on a website. Forgetting to validate absolutely every part of your website or application that interacts with a user is probably the most common mistake you can make. [...] PHP Filters are an extention of PHP that help you to easily - and reliably - validate variables and strings.

He looks at filtering variables with various kinds of filters (defined by the constants) and how to sanitize a string to remove anything but the main textual content.