The unit of a wheel event's deltas, as the DOM's WheelEvent.deltaMode gives it.
public enum WheelDeltaMode
Spec #33 viewer capability 14.
kind:method, kind:property, kind:ctor. Press Esc to clear.LineLines: one line scrolls LineScroll device-independent pixels.PagePages: one page scrolls nine tenths of the viewport.PixelDevice-independent pixels.