bug#29478: 26.0.90; `C-h k' followed by mouse clicks no longer shows down event

[Drew Adams]

> > I would likely never have
> > thought to hold the button pressed for a long time before
> > releasing, just to see what `C-h k' had to tell me.
> 
> Alan, can we arrange for the doc string of mouse-N clicks (with or
> without all the possible modifiers) to say something like
> 
>   For documentation of the corresponding mouse-down event,
>   click and hold the mouse button longer than %s sec.
> 
> (where %s gets replaced by double-click-time)?

That's a hack/workaround, but yes, if we can't do better
then that would definitely help.

If that's at the end of the doc for the up event
then I suspect some users looking for info about
the down event might never notice it.

It should perhaps be made very prominent - ideally
just as prominent as before.  Previously we had two
headings for the two events.  That prominent, whether
done using headings or some other way - that would be
my suggestion.