> #+begin_src emacs-lisp
> (progn
>   (package-initialize)
>   (load-library "consult")
>   (icomplete-vertical-mode t)
>   (keymap-set icomplete-minibuffer-map "C-k" 'icomplete-fido-kill))
> #+end_src
>
> - Then, ``M-x consult-buffer'';
> - Type *M (this should turn the `*Messages*' buffer the current
>   candidate);
> - Then ``C-k''
>
> The following message should appear in the minibuffer:
>
> [Sorry, don’t know how to kill things for ‘multi-category’]

Oh, I see, so the issue is that `consult-buffer` lists not just actual
buffers but also recently visited files and other sources, so it
specifies as `category` the symbol `multi-category` and then it uses
some internal convention about how each completion candidate is
annotated with its type.

> Follows attached!  This is my first patch, so I might have made
> mistakes, but I'm here to adjust whatever you deem necessary.

And your patch adds support to `icomplete.el` for this
specific convention.

There are a few too many things that are "ad-hoc" in that approach for
my taste, but I agree that there's a good justification for adding
support for completion tables that can use a mix of different types and
thus need to offer some way to know further details about the category
of any given completion candidate.

Maybe a better option would be something like the patch below,
so `consult` could define its own method for its own category, which
could even extend the semantics to do thing like delete bookmarks when
applied to bookmarks, etc...


        Stefan