… of course, as soon as I'd posted saying it's very hard to find the ISO 2022 register of character sets, I then tried googling for the one phrase I hadn't yet tried googling for, which was ‘ISO 2022 register of character sets’. And of course that immediately turned up a very plausible-looking thing as the very first link: http://www.itscj.ipsj.or.jp/ISO-IR/.

The bad news is that it appears to support my accusation against Emacs. Looks as if embrace-and-extend isn't a sin unique to proprietary software folks :-(