So far I've figured out that the script editor will auto complete when you press ctrl-enter. Another language editor I used to use had a great feature for newbies that would automatically show the autocompletion options as you type, so as you type "sound." for example it would show the equivalent of what you'd get if you pressed typed "sound." and then pressed ctrl-enter. It would then narrow down the list of options displayed above the cursor as you typed further - or you could select from the list just like you currently can with ctrl-enter. Effectively it was like you pressed ctrl-enter every keypress.
If you choose to implement this it might also be handy to make the auto-completion list semi-transparent so you can see your script behind it?
