PS. By the way, should there be some documentation that describes C-x
    8 commands, as a group [C-h k only responds to, say "C-x 8 ' a" with
    the somewhat useless "á [translated from ...] runs
    self-insert-command"]?

I don't understand those words.

If you mean you want a list of the various possible C-x 8 commands,
you can get that with C-x 8 C-h.