We're probably all a bit rusty on version 6 here (it was originally released back in 2006!) and indeed there have been a lot of new scripts added over that time.
You should be able to find everything in the local documentation (Help menu or hit F1) following a similar path in the tree navigation, like General Survey Help -> Composing Surveys -> SSI Script. There then should be a link on that page for Functions, which groups all the functions into categories (List Functions, System Functions, Quota Functions, etc.).