You might get a better idea by watching a bit of Russ Cox's tour of the Acme editor, in particular the couple of minutes starting around 12:40 [1]. In there he shows how the contents of the various editor windows in the editor are available as files in the filesystem, which means that editor macros can be written in any language that can access the filesystem, without any special bindings.

[1] https://www.youtube.com/watch?v=dP1xVpMPn8M#t=12m42s