>> There is still something missing: `gnus-article-describe-key`
>> already selects the required buffer with `with-current-buffer`.
>> Then why should it provide the same buffer as an argument
>> to `describe-key` to select it again in `describe-key`?
>
> Because `describe-key` otherwise uses the buffer of the window
> associated with the event (this is in done in `help--analyse-key` where
> we currently use `mouse-set-point`).  So we need to pass an explicit
> buffer to tell `describe-key` to ignore the event's window (and we need
> to change this part of `describe-key/help--analyse-key` to obey such a
> buffer argument).
>
>>          (defn (if (not buffer)
>>                    (save-excursion (mouse-set-point event) (key-binding key t))
>>                  (key-binding key t)))
>>
>> IOW, the semantics of `buffer` is not clear here.
>
> If nil it means "defaults to the (window-buffer (posn-window (event-end event)))"
>
>>> OTOH we should probably try and change the `key` arg to use the new
>>> key-list format expected by `describe-key` (i.e. a list of (SEQ
>>> . RAW-SEQ) pairs).
>>
>> `gnus-article-describe-key` just passes down the value
>> that `read-key-sequence` returns.
>
> I know.  This is the old calling convention of `describe-key`; we
> should move to the new one.

Is seems everything is covered by this patch: