Is there already an alist function which gets all matching elements, not just the first?

[Alan Mackenzie]

Hello, Emacs.

I want to be able to get all matching elements from an alist (thinking
about extending imenu).  Something like

    (assoc-all key list)

which would return a list of matches.  After all, we have functions
which _delete_ all matches from an alist.

Does such a function already exist, perhaps in cl-*.el?

Thanks!

-- 
Alan Mackenzie (Nuremberg, Germany).