Tomas Nordin <tomasn@posteo.net> wrote:
> Dmitry Alexandrov <dag@gnui.org> writes:
>> I am not sure, what ‘dummy’ is supposed to mean here?  Minor mode is fully functional, that is you are free to disable and reenable it at will:
>
> I think I sort of tried to be funny, based on that the mode was made up just to keep a key binding available in all situations.

No, itʼs not required there, you are free to enable ‘my-precious-keys-map’ unconditionally as well:

	(add-to-list 'emulation-mode-map-alists
	             (list (cons t my-precious-keys-map)))

if you feel that you will never need to suspend it.

> And that the trickery with the key-maps is hard to follow for me.

There is no any trickery, just a hardcoded priority order in Emacs itself: global map is overridden by major mode map, which in turn is overridden by minor mode maps, which can be overridden by emulation mode maps.

That is, using a minor mode map would suffice in your specific case — about M-o in diff-mode.  But so would a mere:

	(with-eval-after-load 'diff-mode
	  (define-key diff-mode-map
	    (kbd "M-o") nil)) ; also on RET, o, C-c C-c, which is more than enough

> I got the impression that it sufficed to evaluate the forms, I mean, I didn't say, M-x my-precious-keys-mode .

>>>> 	(define-minor-mode my-precious-keys-mode "" t)

| (define-minor-mode MODE DOC &optional INIT-VALUE LIGHTER KEYMAP &rest BODY)
|
| ‹…›
|
| Optional INIT-VALUE is the initial value of the mode’s variable.