Pretty much everything that is known is on
http://chdk.wikia.com/wiki/Canon_Basic and the pages linked from there.
I spent quite a bit of time trying to figure out how to run a canon basic script in shooting mode, but never managed to get it to work. It seems like it should be possible, since lots of the events procs only make sense for shooting. If you can figure out how to do that, you would be able to do a whole lot with canon basic.
The original thread has some discussion of this
http://chdk.setepontos.com/index.php/topic,5549.0.htmlEvent proc usage can be guessed from the name, or from disassembling the firmware.