The amount that is expected to scroll vertically, in units determined by deltaMode.
See also:
WheelEvent.deltaY from the W3C.
Source
@DomName('WheelEvent.deltaY') num get deltaY { if (JS('bool', '#.deltaY !== undefined', this)) { // W3C WheelEvent return this._deltaY; } throw new UnsupportedError('deltaY is not supported'); }