If you're ever posting a piece of code on your blog or whatever, you've probably realized that it's a pain to have to convert any special character to its HTML entity. Why not take the pain away and let PHP handle that for you?
There really isn't a foolproof method to pull this off, and I have been told that traversing the code using the DOM would be better, but this function (as ugly as it is) actually works quite well if you have a proper HTML structure with valid code.
It checks for any <code> and <pre> tags and converts any special characters inside them to there respective HTML entity. It even accounts for nested <code> and <pre> tags, as well as any attributes you give them.