On: Vim's 25th anniversary and the release of Vim 8

[bryogenic]

Also worth noting: Ctrl+[ = ESC in ASCII, which is where the keyboard shortcut comes from.

https://garbagecollected.org/2017/01/31/four-column-ascii/

[inlineint → bryogenic]

And it is processed not by Vim itself, but by the terminal emulator that sends Esc character to Vim. So the shortcut Ctrl+[ was not invented by vi author, but is a consequence of using Esc to exit from the edit mode.