Those brilliantly designed ideas used in Plan 9's 'sam' and 'acme' editors were taken from how Mesa XDE, Mesa/Cedar and Oberon used to work across the whole OS, not just the text editor.

So a proof that even that point needs better research. :)

Since we are on a Lisp thread, same applies to those that just bother with Emacs, eventually SLIME, withouth ever spending one second with actual Common Lisp IDEs.