unload( slide ) {

		// Hide the slide element
		slide.style.display = 'none';

		// Hide the corresponding background element
		let background = this.Reveal.getSlideBackground( slide );
		if( background ) {
			background.style.display = 'none';

			// Unload any background iframes
			queryAll( background, 'iframe[src]' ).forEach( element => {
				element.removeAttribute( 'src' );
			} );
		}

		// Reset lazy-loaded media elements with src attributes
		queryAll( slide, 'video[data-lazy-loaded][src], audio[data-lazy-loaded][src], iframe[data-lazy-loaded][src]' ).forEach( element => {
			element.setAttribute( 'data-src', element.getAttribute( 'src' ) );
			element.removeAttribute( 'src' );
		} );

		// Reset lazy-loaded media elements with <source> children
		queryAll( slide, 'video[data-lazy-loaded] source[src], audio source[src]' ).forEach( source => {
			source.setAttribute( 'data-src', source.getAttribute( 'src' ) );
			source.removeAttribute( 'src' );
		} );

	}
Unloads and hides the given slide. This is called when the
slide is moved outside of the configured view distance.

@param {HTMLElement} slide