onDocumentMouseScroll( event ) {

		if( Date.now() - this.lastMouseWheelStep > 1000 ) {

			this.lastMouseWheelStep = Date.now();

			let delta = event.detail || -event.wheelDelta;
			if( delta > 0 ) {
				this.Reveal.next();
			}
			else if( delta < 0 ) {
				this.Reveal.prev();
			}

		}

	}
Handles mouse wheel scrolling, throttled to avoid skipping
multiple slides.

@param {object} event