Comment 15 for bug 1297051

http://www.vt100.net/ is a good source of information because it uses the original manuals for the real terminals.

http://www.vt100.net/docs/vt510-rm/DA1 defines how \e[c works but it isn't adequate to express the capability of a terminal. In particular it doesn't cater for emulations that are incomplete. There are nowhere near enough attribute values defined to specify what might be missing from an emulation. The specification is unclear as to whether claiming a basic conformance level means that all mandatory features at that level are present. The specification doesn't say what those mandatory features might be. The idea is right.

It's true that we could have defined the answerback response to have a syntax that basically matches the response to \e[c but I think we would need to define the semantics ourselves. That's academic though as gnome-terminal doesn't support an answerback.

I could find no trace on the above-mentioned web site, or any other, of \e[?40h being a valid command in a real terminal. I think it might be an xterm invention.

The TERM variable is problematic with real terminals.