My pet peeve with editors is how they handle files changing underneath them. I do this regularly enough (eg I might make a quick change using vi, source control update), there could be ssh or sshfs involved, or another tool might be better for doing whatever it is that I wanted. Emacs has been the only editor that has never lost a change for me. Whenever you try to make a modification it checks the underlying file is…
Surely not hard to implement (if it's easy to say, it's easy to code, right??)