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

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: lennart.borgman@gmail.com,  5557@debbugs.gnu.org
> Date: Tue, 01 Oct 2019 18:32:24 +0200
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I actually am not sure a click on the margins should produce the same
> > effect as on the text area.  The margins are used to display different
> > text from what's in the text area, so I'm not sure I understand the
> > rationale.
> 
> Oh, I assumed that this was about scrolling, but that's probably not
> what <double-wheel-down> does?

Sorry for confusing wording: it _is_ about scrolling.
double-wheel-down means turning the wheel more than one click down.

What holds me back is that no other area of the display reacts to
mouse-wheel as the text area.  E.g., turning the wheel on the fringes
or on the scroll bar produces the same "undefined" message as for
margins.

I'm guessing that the OP wanted to have the display scrolled no matter
where on display the user turns the mouse wheel, but evidently that's
not how things are defined by default.  If we decide to change that,
it IMO makes little sense to do that only for the margins, but not for
the fringes or the scroll bar.