function handleWheelEvent( tracker, event, originalEvent ) {
        var nDelta = 0,
            eventInfo;

        var eventArgs = null;

        // The nDelta variable is gated to provide smooth z-index scrolling
        //   since the mouse wheel allows for substantial deltas meant for rapid
        //   y-index scrolling.
        // event.deltaMode: 0=pixel, 1=line, 2=page
        // TODO: Deltas in pixel mode should be accumulated then a scroll value computed after $.DEFAULT_SETTINGS.pixelsPerWheelLine threshold reached
        nDelta = event.deltaY ? (event.deltaY < 0 ? 1 : -1) : 0;

        eventInfo = {
            originalEvent: event,
            eventType: 'wheel',
            pointerType: 'mouse',
            isEmulated: event !== originalEvent
        };
        preProcessEvent( tracker, eventInfo );

        if ( tracker.scrollHandler && !eventInfo.preventGesture && !eventInfo.defaultPrevented ) {
            eventArgs = {
                eventSource:          tracker,
                pointerType:          'mouse',
                position:             getMouseRelative( event, tracker.element ),
                scroll:               nDelta,
                shift:                event.shiftKey,
                isTouchEvent:         false,
                originalEvent:        originalEvent,
                preventDefault:       eventInfo.preventDefault || eventInfo.defaultPrevented,
                userData:             tracker.userData
            };


            tracker.scrollHandler( eventArgs );
        }

        if ( eventInfo.stopPropagation ) {
            $.stopEvent( originalEvent );
        }
        if ( ( eventArgs && eventArgs.preventDefault ) || ( eventInfo.preventDefault && !eventInfo.defaultPrevented ) ) {
                $.cancelEvent( originalEvent );
        }
}
Handles 'wheel' events.
The event may be simulated by the legacy mouse wheel event handler (onMouseWheel()).

@private
@inner