*** The new event type `mouse-wheel' is generated by a wheel on a<BR>
mouse (such as the MS Intellimouse).  The event contains a delta that
corresponds to the amount and direction that the wheel is rotated,
which is typically used to implement a scroll or zoom.  The format is:
<P>
  (mouse-wheel POSITION DELTA)
<P>
where POSITION is a list describing the position of the event in the
same format as a mouse-click event, and DELTA is a signed number
indicating the number of increments by which the wheel was rotated.  A
negative DELTA indicates that the wheel was rotated backwards, towards
the user, and a positive DELTA indicates that the wheel was rotated
forward, away from the user.
<P>
As of now, this event type is generated only on MS Windows.
<P>