[Feature request] show commands common string part instead of "Prefix Command"

[stardiviner]

I found guide show deeper keybindings with "[p] Prefix Command" instead of "[p] gist-".

I set some custom keybindings like this:

#+BEGIN_SRC emacs-lisp
(define-prefix-command 'my-tools-prefix-map)
(global-set-key (kbd "C-c t") 'my-tools-prefix-map)

(define-key my-tools-prefix-map (kbd "p p") 'gist-region-or-buffer)
(define-key my-tools-prefix-map (kbd "p v") 'gist-region-or-buffer-private)
(define-key my-tools-prefix-map (kbd "p r") 'gist-region)
(define-key my-tools-prefix-map (kbd "p b") 'gist-buffer)
(define-key my-tools-prefix-map (kbd "p l") 'gist-list)
#+END_SRC

Like upper prefix-map. guide-key just show [p] as Prefix Command instead more
details which can show user info of bind sub-commands.
Like upper code example, guide-key should show [p] gist- instead of [p] Prefix Command.

[hkjels]

Indeed. I have a bunch of these that are mnemonic, so it's not really a problem, but for completeness, it would be nice with such guidance.