Let's say I want to change the function wfReportTime() to not comment out the time, so I can place it somewhere relevant in the skin - but I don't want to modify any files in the /includes/ folder so I can easily upgrade things in the future. How, exactly, would I write an extension that I can just drop in the extensions folder to replace an existing function with my own version? Just so you know, you are talking to pretty much a PHP noob.