OpenGL

What exactly is the Undirect Driver Blacklist and it's purposes? I was toying with Compiz and saw this and didn't want to mess with it until I knew what it was. I had seen a forum/webpage about this topic once but since then, have not been able to find it again. And can you list a few sample entries for it? Currently, mine has the following arguments/options: (nouveau|Intel).*Mesa 8.0