bug#5557: <left-margin> <double-wheel-down> is undefined

[Eli Zaretskii <eliz@gnu.org>]

> From: Stefan Kangas <stefan@marxist.se>
> Date: Fri, 14 Aug 2020 14:34:25 -0700
> Cc: rudalics@gmx.at, larsi@gnus.org, 5557@debbugs.gnu.org, 
> 	lennart.borgman@gmail.com
> 
> Plus I really don't know why someone would want to do anything but
> scroll using the mouse wheel

??? We do that already: C-wheel-up increases the font size.  It
shouldn't be hard to imagine similar bindings on the fringe, for
example.

> OK, I guess we will have to agree to disagree.

Yes.

> One thing I don't understand is how binding to scroll-bar is supposed to
> work.  I tried the following, but it didn't work (tested in GTK and
> lucid):
> 
>     (global-set-key [vertical-scroll-bar mouse-5] 'foo-mouse-message)
>     (defun foo-mouse-message (event)
>       (interactive "e")
>       (message "%s" (format-time-string "%H:%M:%S")))
> 
> (Change vertical-scroll-bar to left-fringe to see that it works there.)

First, you don't need to do anything for vertical-scroll-bar, as the
mouse wheel is already handled there, at least on my system.

On a horizontal scroll-bar, if I use this:

  (global-set-key [horizontal-scroll-bar wheel-up] 'foo-mouse-message)

I get the expected result on my system.

What do you see Emacs say if you turn the wheel on the horizontal
scroll-bar in "emacs -Q"?