The vast majority of the API is documented and the IDE has auto-complete for it. You can find the documentation in the API docs or by clicking the link in the footer of every page.
When we're rolling out a new feature, we often do a "quiet launch" where the code works, but isn't yet documented. We share with with a few alpha users and do further testing in our production environment. Then we do the doc-and-IDE update. However, that process is usually pretty fast - just a couple days. It's not often that we have undocumented features in production.
So, is there something in particular where we're missing the documentation?