What .open and every editor-named spelling of it do, differing only in which editor they mean.

named is the editor the command is named after — .vi means vi — and undefined for the ones that mean whichever the environment prefers. Everything else is one command doing what xdg-open does: with nothing after it the session's own scratchpad, with an address the browser already running, and with anything else an editor, on the file a value is declared in or on the path itself, whether or not there is a file there yet.

import { openingIn } from './editor.ts';

typeof openingIn('vi'); // 'function' — a command's `main`, waiting for a context