> I dislike the vagueness of the term "proprietary."

iTerm2 calls their escape codes proprietary[0]. As far as I can tell, they are not trying to create a standard. VT320, on the other hand, is an ANSI standard[1].

[0] https://www.iterm2.com/documentation-escape-codes.html

[1] https://en.m.wikipedia.org/wiki/VT320

Some day they'll be standards and I'll change the documentation to say "perfectly normal" instead of "proprietary" :)

It's probably a matter of writing a proper RFC like document.

That is how standards should be made.