Ask HN: What's your must-have features in IDE or text editor?

Emacs keybindings.

It must be well-documented, extensible, and have good support for Lisp. IOW, Emacs.

There must be no hints, overlays, suggestions, or predictive insertion of characters as I type. Enabling these distracting features by default is not a fatal flaw, but if I have to spend more than a few minutes figuring out how to disable them, the editor is not likely to get a second chance.