In this new post to his blog, Chris Shiflett helps to solve one of the problems that several web designers face when allowing user input but wanting to protect themselves as well - allowing HTML while preventing a user from including a cross-site scripting issue.

This problem comes up more and more often due to the rise of social networking and other Web 2.0 properties that embolden users. [...] Of course, BBCode inevitably comes up during these types of discussions, but I really hate the idea of using yet another markup language just because I'm too lazy to deal with HTML, especially if the markup language doesn't even try to be user-friendly.

He looks for a good solution, one that doesn't require learning a new markup or becoming overly complex (while avoiding strip_tags). He provides several chunks of code for different aspects of the method - first make the content safe, then move backwards in the translation for the items you want to allow.