IDE that uses an external editor?

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One thing that's kept me from even looking at IDEs is that to the best of my
knowledge none of them will integrate properly with external editors like
Emacs or vi.  I know lots of tools support "Emacs-like keybindings", but
believe me, I've never found one that does a decent job of that.  There is
just so much more to powerful editors like Emacs or vi than a handful of
cursor movement commands.  Once a person is proficient they generally won't
accept substitutes.

So, please prove me wrong.  Are there any IDEs that will actually work with
an external instance of Emacs (either by firing it up or by using a remote
connection program like gnuclient)?

Thx,

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