By defining `foo' with

(defun foo (arg)
  (interactive "p" org-mode)
  (message "foo"))

M-x foo is still available in elisp-mode.

I'm using GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version
3.24.30, cairo version 1.17.4) of 2021-08-16

On Mon, Aug 16, 2021 at 9:24 PM Lars Ingebrigtsen <larsi@gnus.org> wrote:

> Jean-Christophe Helary <lists@traduction-libre.org> writes:
>
> > Ok, that's what I eventually guessed. So, the idea is to check whether
> > a function is interactive and try to guess whether it is limited to a
> > given mode (most probably the mode it is defined in), and if yes tag
> > it ?
>
> Yup.
>
> --
> (domestic pets only, the antidote for overdose, milk.)
>    bloggy blog: http://lars.ingebrigtsen.no
>
>