constructor( Reveal ) {

		this.Reveal = Reveal;

		this.onSlidesClicked = this.onSlidesClicked.bind( this );

		this.iframeTriggerSelector = null;
		this.mediaTriggerSelector = '[data-preview-image], [data-preview-video]';

		this.stateProps = ['previewIframe', 'previewImage', 'previewVideo', 'previewFit'];
		this.state = {};

	}
Handles the display of reveal.js' overlay elements used
to preview iframes, images & videos.