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.