The "editor" setting:

The value is an external command that will launch the text editor command used for check-in comments.

If this value is not set, then environment variables VISUAL and EDITOR are consulted, in that order. If neither of those are set, then a search is made for common text editors, including "notepad", "nano", "pico", "jove", "edit", "vi", "vim", and "ed".

If this setting is false ("off", "no", "false", or "0") then no text editor is used.