Alex suggested adding hover tooltips with docs in the editor for API functions, objects, etc. There should also be a way to turn this off because it's sort of in-your-face if you're not trying to pull up the tooltips.
Look into using HoverTooltip. The Ace source is really badly (not at all) documented, so you'll need to read the source code to figure out how it works and read the tests for examples of usage.

Related files: Editor.tsx