showHelp() {

		if( this.Reveal.getConfig().help ) {

			this.close();

			this.createOverlay( 'r-overlay-help' );

			let html = '<p class="title">Keyboard Shortcuts</p>';

			let shortcuts = this.Reveal.keyboard.getShortcuts(),
				bindings = this.Reveal.keyboard.getBindings();

			html += '<table><th>KEY</th><th>ACTION</th>';
			for( let key in shortcuts ) {
				html += `<tr><td>${key}</td><td>${shortcuts[ key ]}</td></tr>`;
			}

			// Add custom key bindings that have associated descriptions
			for( let binding in bindings ) {
				if( bindings[binding].key && bindings[binding].description ) {
					html += `<tr><td>${bindings[binding].key}</td><td>${bindings[binding].description}</td></tr>`;
				}
			}

			html += '</table>';

			this.viewport.innerHTML = `
				<header class="r-overlay-header">
					<button class="r-overlay-button r-overlay-close">Esc <span class="icon"></span></button>
				</header>
				<div class="r-overlay-content">
					<div class="r-overlay-help-content">${html}</div>
				</div>
			`;

			this.dom.querySelector( '.r-overlay-close' ).addEventListener( 'click', event => {
				this.close();
				event.preventDefault();
			}, false );

			this.Reveal.dispatchEvent({ type: 'showhelp' });

		}

	}
Opens an overlay window with help material.