infra/js/reveal.js

/*!
 * reveal.js
 * http://lab.hakim.se/reveal-js
 * MIT licensed
 *
 * Copyright (C) 2013 Hakim El Hattab, http://hakim.se
 */
var Reveal = (function(){

	'use strict';

	var SLIDES_SELECTOR = '.reveal .slides section',
		HORIZONTAL_SLIDES_SELECTOR = '.reveal .slides>section',
		VERTICAL_SLIDES_SELECTOR = '.reveal .slides>section.present>section',
		HOME_SLIDE_SELECTOR = '.reveal .slides>section:first-child',

		// Configurations defaults, can be overridden at initialization time
		config = {

			// The "normal" size of the presentation, aspect ratio will be preserved
			// when the presentation is scaled to fit different resolutions
			width: 960,
			height: 700,

			// Factor of the display size that should remain empty around the content
			margin: 0.1,

			// Bounds for smallest/largest possible scale to apply to content
			minScale: 0.2,
			maxScale: 1.0,

			// Display controls in the bottom right corner
			controls: true,

			// Display a presentation progress bar
			progress: true,

			// Push each slide change to the browser history
			history: false,

			// Enable keyboard shortcuts for navigation
			keyboard: true,

			// Enable the slide overview mode
			overview: true,

			// Vertical centring of slides
			center: true,

			// Enables touch navigation on devices with touch input
			touch: true,

			// Loop the presentation
			loop: false,

			// Change the presentation direction to be RTL
			rtl: false,

			// Turns fragments on and off globally
			fragments: true,

			// Flags if the presentation is running in an embedded mode,
			// i.e. contained within a limited portion of the screen
			embedded: false,

			// Number of milliseconds between automatically proceeding to the
			// next slide, disabled when set to 0, this value can be overwritten
			// by using a data-autoslide attribute on your slides
			autoSlide: 0,

			// Enable slide navigation via mouse wheel
			mouseWheel: false,

			// Apply a 3D roll to links on hover
			rollingLinks: false,

			// Opens links in an iframe preview overlay
			previewLinks: false,

			// Theme (see /css/theme)
			theme: null,

			// Transition style
			transition: 'default', // default/cube/page/concave/zoom/linear/fade/none

			// Transition speed
			transitionSpeed: 'default', // default/fast/slow

			// Transition style for full page slide backgrounds
			backgroundTransition: 'default', // default/linear/none

			// Number of slides away from the current that are visible
			viewDistance: 3,

			// Script dependencies to load
			dependencies: []
		},

		// Flags if reveal.js is loaded (has dispatched the 'ready' event)
		loaded = false,

		// The current auto-slide duration
		autoSlide = 0,

		// The horizontal and vertical index of the currently active slide
		indexh,
		indexv,

		// The previous and current slide HTML elements
		previousSlide,
		currentSlide,

		// Slides may hold a data-state attribute which we pick up and apply
		// as a class to the body. This list contains the combined state of
		// all current slides.
		state = [],

		// The current scale of the presentation (see width/height config)
		scale = 1,

		// Cached references to DOM elements
		dom = {},

		// Client support for CSS 3D transforms, see #checkCapabilities()
		supports3DTransforms,

		// Client support for CSS 2D transforms, see #checkCapabilities()
		supports2DTransforms,

		// Client is a mobile device, see #checkCapabilities()
		isMobileDevice,

		// Throttles mouse wheel navigation
		lastMouseWheelStep = 0,

		// An interval used to automatically move on to the next slide
		autoSlideTimeout = 0,

		// Delays updates to the URL due to a Chrome thumbnailer bug
		writeURLTimeout = 0,

		// A delay used to activate the overview mode
		activateOverviewTimeout = 0,

		// A delay used to deactivate the overview mode
		deactivateOverviewTimeout = 0,

		// Flags if the interaction event listeners are bound
		eventsAreBound = false,

		// Holds information about the currently ongoing touch input
		touch = {
			startX: 0,
			startY: 0,
			startSpan: 0,
			startCount: 0,
			captured: false,
			threshold: 40
		};

	/**
	 * Starts up the presentation if the client is capable.
	 */
	function initialize( options ) {

		checkCapabilities();

		if( !supports2DTransforms && !supports3DTransforms ) {
			document.body.setAttribute( 'class', 'no-transforms' );

			// If the browser doesn't support core features we won't be
			// using JavaScript to control the presentation
			return;
		}

		// Force a layout when the whole page, incl fonts, has loaded
		window.addEventListener( 'load', layout, false );

		// Copy options over to our config object
		extend( config, options );

		// Hide the address bar in mobile browsers
		hideAddressBar();

		// Loads the dependencies and continues to #start() once done
		load();

	}

	/**
	 * Inspect the client to see what it's capable of, this
	 * should only happens once per runtime.
	 */
	function checkCapabilities() {

		supports3DTransforms =  'WebkitPerspective' in document.body.style ||
								'MozPerspective' in document.body.style ||
								'msPerspective' in document.body.style ||
								'OPerspective' in document.body.style ||
								'perspective' in document.body.style;

		supports2DTransforms =  'WebkitTransform' in document.body.style ||
								'MozTransform' in document.body.style ||
								'msTransform' in document.body.style ||
								'OTransform' in document.body.style ||
								'transform' in document.body.style;

		isMobileDevice = navigator.userAgent.match( /(iphone|ipod|android)/gi );

	}

	/**
	 * Loads the dependencies of reveal.js. Dependencies are
	 * defined via the configuration option 'dependencies'
	 * and will be loaded prior to starting/binding reveal.js.
	 * Some dependencies may have an 'async' flag, if so they
	 * will load after reveal.js has been started up.
	 */
	function load() {

		var scripts = [],
			scriptsAsync = [];

		for( var i = 0, len = config.dependencies.length; i < len; i++ ) {
			var s = config.dependencies[i];

			// Load if there's no condition or the condition is truthy
			if( !s.condition || s.condition() ) {
				if( s.async ) {
					scriptsAsync.push( s.src );
				}
				else {
					scripts.push( s.src );
				}

				// Extension may contain callback functions
				if( typeof s.callback === 'function' ) {
					head.ready( s.src.match( /([\w\d_\-]*)\.?js$|[^\\\/]*$/i )[0], s.callback );
				}
			}
		}

		// Called once synchronous scripts finish loading
		function proceed() {
			if( scriptsAsync.length ) {
				// Load asynchronous scripts
				head.js.apply( null, scriptsAsync );
			}

			start();
		}

		if( scripts.length ) {
			head.ready( proceed );

			// Load synchronous scripts
			head.js.apply( null, scripts );
		}
		else {
			proceed();
		}

	}

	/**
	 * Starts up reveal.js by binding input events and navigating
	 * to the current URL deeplink if there is one.
	 */
	function start() {

		// Make sure we've got all the DOM elements we need
		setupDOM();

		// Decorate the slide DOM elements with state classes (past/future)
		setupSlides();

		// Updates the presentation to match the current configuration values
		configure();

		// Read the initial hash
		readURL();

		// Notify listeners that the presentation is ready but use a 1ms
		// timeout to ensure it's not fired synchronously after #initialize()
		setTimeout( function() {
			// Enable transitions now that we're loaded
			dom.slides.classList.remove( 'no-transition' );

			loaded = true;

			dispatchEvent( 'ready', {
				'indexh': indexh,
				'indexv': indexv,
				'currentSlide': currentSlide
			} );
		}, 1 );

	}

	/**
	 * Iterates through and decorates slides DOM elements with
	 * appropriate classes.
	 */
	function setupSlides() {

		var horizontalSlides = toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );
		horizontalSlides.forEach( function( horizontalSlide ) {

			var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) );
			verticalSlides.forEach( function( verticalSlide, y ) {

				if( y > 0 ) verticalSlide.classList.add( 'future' );

			} );

		} );

	}

	/**
	 * Finds and stores references to DOM elements which are
	 * required by the presentation. If a required element is
	 * not found, it is created.
	 */
	function setupDOM() {

		// Cache references to key DOM elements
		dom.theme = document.querySelector( '#theme' );
		dom.wrapper = document.querySelector( '.reveal' );
		dom.slides = document.querySelector( '.reveal .slides' );

		// Prevent transitions while we're loading
		dom.slides.classList.add( 'no-transition' );

		// Background element
		dom.background = createSingletonNode( dom.wrapper, 'div', 'backgrounds', null );

		// Progress bar
		dom.progress = createSingletonNode( dom.wrapper, 'div', 'progress', '<span></span>' );
		dom.progressbar = dom.progress.querySelector( 'span' );

		// Arrow controls
		createSingletonNode( dom.wrapper, 'aside', 'controls',
			'<div class="navigate-left"></div>' +
			'<div class="navigate-right"></div>' +
			'<div class="navigate-up"></div>' +
			'<div class="navigate-down"></div>' );

		// State background element [DEPRECATED]
		createSingletonNode( dom.wrapper, 'div', 'state-background', null );

		// Overlay graphic which is displayed during the paused mode
		createSingletonNode( dom.wrapper, 'div', 'pause-overlay', null );

		// Cache references to elements
		if ( config.controls ) {
			dom.controls = document.querySelector( '.reveal .controls' );

			// There can be multiple instances of controls throughout the page
			dom.controlsLeft = toArray( document.querySelectorAll( '.navigate-left' ) );
			dom.controlsRight = toArray( document.querySelectorAll( '.navigate-right' ) );
			dom.controlsUp = toArray( document.querySelectorAll( '.navigate-up' ) );
			dom.controlsDown = toArray( document.querySelectorAll( '.navigate-down' ) );
			dom.controlsPrev = toArray( document.querySelectorAll( '.navigate-prev' ) );
			dom.controlsNext = toArray( document.querySelectorAll( '.navigate-next' ) );
		}

	}

	/**
	 * Creates an HTML element and returns a reference to it.
	 * If the element already exists the existing instance will
	 * be returned.
	 */
	function createSingletonNode( container, tagname, classname, innerHTML ) {

		var node = container.querySelector( '.' + classname );
		if( !node ) {
			node = document.createElement( tagname );
			node.classList.add( classname );
			if( innerHTML !== null ) {
				node.innerHTML = innerHTML;
			}
			container.appendChild( node );
		}
		return node;

	}

	/**
	 * Creates the slide background elements and appends them
	 * to the background container. One element is created per
	 * slide no matter if the given slide has visible background.
	 */
	function createBackgrounds() {

		if( isPrintingPDF() ) {
			document.body.classList.add( 'print-pdf' );
		}

		// Clear prior backgrounds
		dom.background.innerHTML = '';
		dom.background.classList.add( 'no-transition' );

		// Helper method for creating a background element for the
		// given slide
		function _createBackground( slide, container ) {

			var data = {
				background: slide.getAttribute( 'data-background' ),
				backgroundSize: slide.getAttribute( 'data-background-size' ),
				backgroundImage: slide.getAttribute( 'data-background-image' ),
				backgroundColor: slide.getAttribute( 'data-background-color' ),
				backgroundRepeat: slide.getAttribute( 'data-background-repeat' ),
				backgroundPosition: slide.getAttribute( 'data-background-position' ),
				backgroundTransition: slide.getAttribute( 'data-background-transition' )
			};

			var element = document.createElement( 'div' );
			element.className = 'slide-background';

			if( data.background ) {
				// Auto-wrap image urls in url(...)
				if( /^(http|file|\/\/)/gi.test( data.background ) || /\.(png|jpg|jpeg|gif|bmp)$/gi.test( data.background ) ) {
					element.style.backgroundImage = 'url('+ data.background +')';
				}
				else {
					element.style.background = data.background;
				}
			}

			// Additional and optional background properties
			if( data.backgroundSize ) element.style.backgroundSize = data.backgroundSize;
			if( data.backgroundImage ) element.style.backgroundImage = 'url("' + data.backgroundImage + '")';
			if( data.backgroundColor ) element.style.backgroundColor = data.backgroundColor;
			if( data.backgroundRepeat ) element.style.backgroundRepeat = data.backgroundRepeat;
			if( data.backgroundPosition ) element.style.backgroundPosition = data.backgroundPosition;
			if( data.backgroundTransition ) element.setAttribute( 'data-background-transition', data.backgroundTransition );

			container.appendChild( element );

			return element;

		}

		// Iterate over all horizontal slides
		toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).forEach( function( slideh ) {

			var backgroundStack;

			if( isPrintingPDF() ) {
				backgroundStack = _createBackground( slideh, slideh );
			}
			else {
				backgroundStack = _createBackground( slideh, dom.background );
			}

			// Iterate over all vertical slides
			toArray( slideh.querySelectorAll( 'section' ) ).forEach( function( slidev ) {

				if( isPrintingPDF() ) {
					_createBackground( slidev, slidev );
				}
				else {
					_createBackground( slidev, backgroundStack );
				}

			} );

		} );

	}

	/**
	 * Applies the configuration settings from the config
	 * object. May be called multiple times.
	 */
	function configure( options ) {

		dom.wrapper.classList.remove( config.transition );

		// New config options may be passed when this method
		// is invoked through the API after initialization
		if( typeof options === 'object' ) extend( config, options );

		// Force linear transition based on browser capabilities
		if( supports3DTransforms === false ) config.transition = 'linear';

		dom.wrapper.classList.add( config.transition );

		dom.wrapper.setAttribute( 'data-transition-speed', config.transitionSpeed );
		dom.wrapper.setAttribute( 'data-background-transition', config.backgroundTransition );

		if( dom.controls ) {
			dom.controls.style.display = ( config.controls && dom.controls ) ? 'block' : 'none';
		}

		if( dom.progress ) {
			dom.progress.style.display = ( config.progress && dom.progress ) ? 'block' : 'none';
		}

		if( config.rtl ) {
			dom.wrapper.classList.add( 'rtl' );
		}
		else {
			dom.wrapper.classList.remove( 'rtl' );
		}

		if( config.center ) {
			dom.wrapper.classList.add( 'center' );
		}
		else {
			dom.wrapper.classList.remove( 'center' );
		}

		if( config.mouseWheel ) {
			document.addEventListener( 'DOMMouseScroll', onDocumentMouseScroll, false ); // FF
			document.addEventListener( 'mousewheel', onDocumentMouseScroll, false );
		}
		else {
			document.removeEventListener( 'DOMMouseScroll', onDocumentMouseScroll, false ); // FF
			document.removeEventListener( 'mousewheel', onDocumentMouseScroll, false );
		}

		// Rolling 3D links
		if( config.rollingLinks ) {
			enableRollingLinks();
		}
		else {
			disableRollingLinks();
		}

		// Iframe link previews
		if( config.previewLinks ) {
			enablePreviewLinks();
		}
		else {
			disablePreviewLinks();
			enablePreviewLinks( '[data-preview-link]' );
		}

		// Load the theme in the config, if it's not already loaded
		if( config.theme && dom.theme ) {
			var themeURL = dom.theme.getAttribute( 'href' );
			var themeFinder = /[^\/]*?(?=\.css)/;
			var themeName = themeURL.match(themeFinder)[0];

			if(  config.theme !== themeName ) {
				themeURL = themeURL.replace(themeFinder, config.theme);
				dom.theme.setAttribute( 'href', themeURL );
			}
		}

		sync();

	}

	/**
	 * Binds all event listeners.
	 */
	function addEventListeners() {

		eventsAreBound = true;

		window.addEventListener( 'hashchange', onWindowHashChange, false );
		window.addEventListener( 'resize', onWindowResize, false );

		if( config.touch ) {
			dom.wrapper.addEventListener( 'touchstart', onTouchStart, false );
			dom.wrapper.addEventListener( 'touchmove', onTouchMove, false );
			dom.wrapper.addEventListener( 'touchend', onTouchEnd, false );

			// Support pointer-style touch interaction as well
			if( window.navigator.msPointerEnabled ) {
				dom.wrapper.addEventListener( 'MSPointerDown', onPointerDown, false );
				dom.wrapper.addEventListener( 'MSPointerMove', onPointerMove, false );
				dom.wrapper.addEventListener( 'MSPointerUp', onPointerUp, false );
			}
		}

		if( config.keyboard ) {
			document.addEventListener( 'keydown', onDocumentKeyDown, false );
		}

		if ( config.progress && dom.progress ) {
			dom.progress.addEventListener( 'click', onProgressClicked, false );
		}

		if ( config.controls && dom.controls ) {
			[ 'touchstart', 'click' ].forEach( function( eventName ) {
				dom.controlsLeft.forEach( function( el ) { el.addEventListener( eventName, onNavigateLeftClicked, false ); } );
				dom.controlsRight.forEach( function( el ) { el.addEventListener( eventName, onNavigateRightClicked, false ); } );
				dom.controlsUp.forEach( function( el ) { el.addEventListener( eventName, onNavigateUpClicked, false ); } );
				dom.controlsDown.forEach( function( el ) { el.addEventListener( eventName, onNavigateDownClicked, false ); } );
				dom.controlsPrev.forEach( function( el ) { el.addEventListener( eventName, onNavigatePrevClicked, false ); } );
				dom.controlsNext.forEach( function( el ) { el.addEventListener( eventName, onNavigateNextClicked, false ); } );
			} );
		}

	}

	/**
	 * Unbinds all event listeners.
	 */
	function removeEventListeners() {

		eventsAreBound = false;

		document.removeEventListener( 'keydown', onDocumentKeyDown, false );
		window.removeEventListener( 'hashchange', onWindowHashChange, false );
		window.removeEventListener( 'resize', onWindowResize, false );

		dom.wrapper.removeEventListener( 'touchstart', onTouchStart, false );
		dom.wrapper.removeEventListener( 'touchmove', onTouchMove, false );
		dom.wrapper.removeEventListener( 'touchend', onTouchEnd, false );

		if( window.navigator.msPointerEnabled ) {
			dom.wrapper.removeEventListener( 'MSPointerDown', onPointerDown, false );
			dom.wrapper.removeEventListener( 'MSPointerMove', onPointerMove, false );
			dom.wrapper.removeEventListener( 'MSPointerUp', onPointerUp, false );
		}

		if ( config.progress && dom.progress ) {
			dom.progress.removeEventListener( 'click', onProgressClicked, false );
		}

		if ( config.controls && dom.controls ) {
			[ 'touchstart', 'click' ].forEach( function( eventName ) {
				dom.controlsLeft.forEach( function( el ) { el.removeEventListener( eventName, onNavigateLeftClicked, false ); } );
				dom.controlsRight.forEach( function( el ) { el.removeEventListener( eventName, onNavigateRightClicked, false ); } );
				dom.controlsUp.forEach( function( el ) { el.removeEventListener( eventName, onNavigateUpClicked, false ); } );
				dom.controlsDown.forEach( function( el ) { el.removeEventListener( eventName, onNavigateDownClicked, false ); } );
				dom.controlsPrev.forEach( function( el ) { el.removeEventListener( eventName, onNavigatePrevClicked, false ); } );
				dom.controlsNext.forEach( function( el ) { el.removeEventListener( eventName, onNavigateNextClicked, false ); } );
			} );
		}

	}

	/**
	 * Extend object a with the properties of object b.
	 * If there's a conflict, object b takes precedence.
	 */
	function extend( a, b ) {

		for( var i in b ) {
			a[ i ] = b[ i ];
		}

	}

	/**
	 * Converts the target object to an array.
	 */
	function toArray( o ) {

		return Array.prototype.slice.call( o );

	}

	/**
	 * Measures the distance in pixels between point a
	 * and point b.
	 *
	 * @param {Object} a point with x/y properties
	 * @param {Object} b point with x/y properties
	 */
	function distanceBetween( a, b ) {

		var dx = a.x - b.x,
			dy = a.y - b.y;

		return Math.sqrt( dx*dx + dy*dy );

	}

	/**
	 * Applies a CSS transform to the target element.
	 */
	function transformElement( element, transform ) {

		element.style.WebkitTransform = transform;
		element.style.MozTransform = transform;
		element.style.msTransform = transform;
		element.style.OTransform = transform;
		element.style.transform = transform;

	}

	/**
	 * Retrieves the height of the given element by looking
	 * at the position and height of its immediate children.
	 */
	function getAbsoluteHeight( element ) {

		var height = 0;

		if( element ) {
			var absoluteChildren = 0;

			toArray( element.childNodes ).forEach( function( child ) {

				if( typeof child.offsetTop === 'number' && child.style ) {
					// Count # of abs children
					if( child.style.position === 'absolute' ) {
						absoluteChildren += 1;
					}

					height = Math.max( height, child.offsetTop + child.offsetHeight );
				}

			} );

			// If there are no absolute children, use offsetHeight
			if( absoluteChildren === 0 ) {
				height = element.offsetHeight;
			}

		}

		return height;

	}

	/**
	 * Returns the remaining height within the parent of the
	 * target element after subtracting the height of all
	 * siblings.
	 *
	 * remaining height = [parent height] - [ siblings height]
	 */
	function getRemainingHeight( element, height ) {

		height = height || 0;

		if( element ) {
			var parent = element.parentNode;
			var siblings = parent.childNodes;

			// Subtract the height of each sibling
			toArray( siblings ).forEach( function( sibling ) {

				if( typeof sibling.offsetHeight === 'number' && sibling !== element ) {

					var styles = window.getComputedStyle( sibling ),
						marginTop = parseInt( styles.marginTop, 10 ),
						marginBottom = parseInt( styles.marginBottom, 10 );

					height -= sibling.offsetHeight + marginTop + marginBottom;

				}

			} );

			var elementStyles = window.getComputedStyle( element );

			// Subtract the margins of the target element
			height -= parseInt( elementStyles.marginTop, 10 ) +
						parseInt( elementStyles.marginBottom, 10 );

		}

		return height;

	}

	/**
	 * Checks if this instance is being used to print a PDF.
	 */
	function isPrintingPDF() {

		return ( /print-pdf/gi ).test( window.location.search );

	}

	/**
	 * Hides the address bar if we're on a mobile device.
	 */
	function hideAddressBar() {

		if( /iphone|ipod|android/gi.test( navigator.userAgent ) && !/crios/gi.test( navigator.userAgent ) ) {
			// Events that should trigger the address bar to hide
			window.addEventListener( 'load', removeAddressBar, false );
			window.addEventListener( 'orientationchange', removeAddressBar, false );
		}

	}

	/**
	 * Causes the address bar to hide on mobile devices,
	 * more vertical space ftw.
	 */
	function removeAddressBar() {

		if( window.orientation === 0 ) {
			document.documentElement.style.overflow = 'scroll';
			document.body.style.height = '120%';
		}
		else {
			document.documentElement.style.overflow = '';
			document.body.style.height = '100%';
		}

		setTimeout( function() {
			window.scrollTo( 0, 1 );
		}, 10 );

	}

	/**
	 * Dispatches an event of the specified type from the
	 * reveal DOM element.
	 */
	function dispatchEvent( type, properties ) {

		var event = document.createEvent( "HTMLEvents", 1, 2 );
		event.initEvent( type, true, true );
		extend( event, properties );
		dom.wrapper.dispatchEvent( event );

	}

	/**
	 * Wrap all links in 3D goodness.
	 */
	function enableRollingLinks() {

		if( supports3DTransforms && !( 'msPerspective' in document.body.style ) ) {
			var anchors = document.querySelectorAll( SLIDES_SELECTOR + ' a:not(.image)' );

			for( var i = 0, len = anchors.length; i < len; i++ ) {
				var anchor = anchors[i];

				if( anchor.textContent && !anchor.querySelector( '*' ) && ( !anchor.className || !anchor.classList.contains( anchor, 'roll' ) ) ) {
					var span = document.createElement('span');
					span.setAttribute('data-title', anchor.text);
					span.innerHTML = anchor.innerHTML;

					anchor.classList.add( 'roll' );
					anchor.innerHTML = '';
					anchor.appendChild(span);
				}
			}
		}

	}

	/**
	 * Unwrap all 3D links.
	 */
	function disableRollingLinks() {

		var anchors = document.querySelectorAll( SLIDES_SELECTOR + ' a.roll' );

		for( var i = 0, len = anchors.length; i < len; i++ ) {
			var anchor = anchors[i];
			var span = anchor.querySelector( 'span' );

			if( span ) {
				anchor.classList.remove( 'roll' );
				anchor.innerHTML = span.innerHTML;
			}
		}

	}

	/**
	 * Bind preview frame links.
	 */
	function enablePreviewLinks( selector ) {

		var anchors = toArray( document.querySelectorAll( selector ? selector : 'a' ) );

		anchors.forEach( function( element ) {
			if( /^(http|www)/gi.test( element.getAttribute( 'href' ) ) ) {
				element.addEventListener( 'click', onPreviewLinkClicked, false );
			}
		} );

	}

	/**
	 * Unbind preview frame links.
	 */
	function disablePreviewLinks() {

		var anchors = toArray( document.querySelectorAll( 'a' ) );

		anchors.forEach( function( element ) {
			if( /^(http|www)/gi.test( element.getAttribute( 'href' ) ) ) {
				element.removeEventListener( 'click', onPreviewLinkClicked, false );
			}
		} );

	}

	/**
	 * Opens a preview window for the target URL.
	 */
	function openPreview( url ) {

		closePreview();

		dom.preview = document.createElement( 'div' );
		dom.preview.classList.add( 'preview-link-overlay' );
		dom.wrapper.appendChild( dom.preview );

		dom.preview.innerHTML = [
			'<header>',
				'<a class="close" href="#"><span class="icon"></span></a>',
				'<a class="external" href="'+ url +'" target="_blank"><span class="icon"></span></a>',
			'</header>',
			'<div class="spinner"></div>',
			'<div class="viewport">',
				'<iframe src="'+ url +'"></iframe>',
			'</div>'
		].join('');

		dom.preview.querySelector( 'iframe' ).addEventListener( 'load', function( event ) {
			dom.preview.classList.add( 'loaded' );
		}, false );

		dom.preview.querySelector( '.close' ).addEventListener( 'click', function( event ) {
			closePreview();
			event.preventDefault();
		}, false );

		dom.preview.querySelector( '.external' ).addEventListener( 'click', function( event ) {
			closePreview();
		}, false );

		setTimeout( function() {
			dom.preview.classList.add( 'visible' );
		}, 1 );

	}

	/**
	 * Closes the iframe preview window.
	 */
	function closePreview() {

		if( dom.preview ) {
			dom.preview.setAttribute( 'src', '' );
			dom.preview.parentNode.removeChild( dom.preview );
			dom.preview = null;
		}

	}

	/**
	 * Return a sorted fragments list, ordered by an increasing
	 * "data-fragment-index" attribute.
	 *
	 * Fragments will be revealed in the order that they are returned by
	 * this function, so you can use the index attributes to control the
	 * order of fragment appearance.
	 *
	 * To maintain a sensible default fragment order, fragments are presumed
	 * to be passed in document order. This function adds a "fragment-index"
	 * attribute to each node if such an attribute is not already present,
	 * and sets that attribute to an integer value which is the position of
	 * the fragment within the fragments list.
	 */
	function sortFragments( fragments ) {

		var a = toArray( fragments );

		a.forEach( function( el, idx ) {
			if( !el.hasAttribute( 'data-fragment-index' ) ) {
				el.setAttribute( 'data-fragment-index', idx );
			}
		} );

		a.sort( function( l, r ) {
			return l.getAttribute( 'data-fragment-index' ) - r.getAttribute( 'data-fragment-index');
		} );

		return a;

	}

	/**
	 * Applies JavaScript-controlled layout rules to the
	 * presentation.
	 */
	function layout() {

		if( dom.wrapper && !isPrintingPDF() ) {

			// Available space to scale within
			var availableWidth = dom.wrapper.offsetWidth,
				availableHeight = dom.wrapper.offsetHeight;

			// Reduce available space by margin
			availableWidth -= ( availableHeight * config.margin );
			availableHeight -= ( availableHeight * config.margin );

			// Dimensions of the content
			var slideWidth = config.width,
				slideHeight = config.height,
				slidePadding = 20; // TODO Dig this out of DOM

			// Layout the contents of the slides
			layoutSlideContents( config.width, config.height, slidePadding );

			// Slide width may be a percentage of available width
			if( typeof slideWidth === 'string' && /%$/.test( slideWidth ) ) {
				slideWidth = parseInt( slideWidth, 10 ) / 100 * availableWidth;
			}

			// Slide height may be a percentage of available height
			if( typeof slideHeight === 'string' && /%$/.test( slideHeight ) ) {
				slideHeight = parseInt( slideHeight, 10 ) / 100 * availableHeight;
			}

			dom.slides.style.width = slideWidth + 'px';
			dom.slides.style.height = slideHeight + 'px';

			// Determine scale of content to fit within available space
			scale = Math.min( availableWidth / slideWidth, availableHeight / slideHeight );

			// Respect max/min scale settings
			scale = Math.max( scale, config.minScale );
			scale = Math.min( scale, config.maxScale );

			// Prefer applying scale via zoom since Chrome blurs scaled content
			// with nested transforms
			if( typeof dom.slides.style.zoom !== 'undefined' && !navigator.userAgent.match( /(iphone|ipod|ipad|android)/gi ) ) {
				dom.slides.style.zoom = scale;
			}
			// Apply scale transform as a fallback
			else {
				transformElement( dom.slides, 'translate(-50%, -50%) scale('+ scale +') translate(50%, 50%)' );
			}

			// Select all slides, vertical and horizontal
			var slides = toArray( document.querySelectorAll( SLIDES_SELECTOR ) );

			for( var i = 0, len = slides.length; i < len; i++ ) {
				var slide = slides[ i ];

				// Don't bother updating invisible slides
				if( slide.style.display === 'none' ) {
					continue;
				}

				if( config.center ) {
					// Vertical stacks are not centred since their section
					// children will be
					if( slide.classList.contains( 'stack' ) ) {
						slide.style.top = 0;
					}
					else {
						slide.style.top = Math.max( - ( getAbsoluteHeight( slide ) / 2 ) - slidePadding, -slideHeight / 2 ) + 'px';
					}
				}
				else {
					slide.style.top = '';
				}

			}

			updateProgress();

		}

	}

	/**
	 * Applies layout logic to the contents of all slides in
	 * the presentation.
	 */
	function layoutSlideContents( width, height, padding ) {

		// Handle sizing of elements with the 'stretch' class
		toArray( dom.slides.querySelectorAll( 'section > .stretch' ) ).forEach( function( element ) {

			// Determine how much vertical space we can use
			var remainingHeight = getRemainingHeight( element, ( height - ( padding * 2 ) ) );

			// Consider the aspect ratio of media elements
			if( /(img|video)/gi.test( element.nodeName ) ) {
				var nw = element.naturalWidth || element.videoWidth,
					nh = element.naturalHeight || element.videoHeight;

				var es = Math.min( width / nw, remainingHeight / nh );

				element.style.width = ( nw * es ) + 'px';
				element.style.height = ( nh * es ) + 'px';

			}
			else {
				element.style.width = width + 'px';
				element.style.height = remainingHeight + 'px';
			}

		} );

	}

	/**
	 * Stores the vertical index of a stack so that the same
	 * vertical slide can be selected when navigating to and
	 * from the stack.
	 *
	 * @param {HTMLElement} stack The vertical stack element
	 * @param {int} v Index to memorize
	 */
	function setPreviousVerticalIndex( stack, v ) {

		if( typeof stack === 'object' && typeof stack.setAttribute === 'function' ) {
			stack.setAttribute( 'data-previous-indexv', v || 0 );
		}

	}

	/**
	 * Retrieves the vertical index which was stored using
	 * #setPreviousVerticalIndex() or 0 if no previous index
	 * exists.
	 *
	 * @param {HTMLElement} stack The vertical stack element
	 */
	function getPreviousVerticalIndex( stack ) {

		if( typeof stack === 'object' && typeof stack.setAttribute === 'function' && stack.classList.contains( 'stack' ) ) {
			// Prefer manually defined start-indexv
			var attributeName = stack.hasAttribute( 'data-start-indexv' ) ? 'data-start-indexv' : 'data-previous-indexv';

			return parseInt( stack.getAttribute( attributeName ) || 0, 10 );
		}

		return 0;

	}

	/**
	 * Displays the overview of slides (quick nav) by
	 * scaling down and arranging all slide elements.
	 *
	 * Experimental feature, might be dropped if perf
	 * can't be improved.
	 */
	function activateOverview() {

		// Only proceed if enabled in config
		if( config.overview ) {

			// Don't auto-slide while in overview mode
			cancelAutoSlide();

			var wasActive = dom.wrapper.classList.contains( 'overview' );

			// Vary the depth of the overview based on screen size
			var depth = window.innerWidth < 400 ? 1000 : 2500;

			dom.wrapper.classList.add( 'overview' );
			dom.wrapper.classList.remove( 'exit-overview' );

			clearTimeout( activateOverviewTimeout );
			clearTimeout( deactivateOverviewTimeout );

			// Not the pretties solution, but need to let the overview
			// class apply first so that slides are measured accurately
			// before we can position them
			activateOverviewTimeout = setTimeout( function(){

				var horizontalSlides = document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR );

				for( var i = 0, len1 = horizontalSlides.length; i < len1; i++ ) {
					var hslide = horizontalSlides[i],
						hoffset = config.rtl ? -105 : 105;

					hslide.setAttribute( 'data-index-h', i );

					// Apply CSS transform
					transformElement( hslide, 'translateZ(-'+ depth +'px) translate(' + ( ( i - indexh ) * hoffset ) + '%, 0%)' );

					if( hslide.classList.contains( 'stack' ) ) {

						var verticalSlides = hslide.querySelectorAll( 'section' );

						for( var j = 0, len2 = verticalSlides.length; j < len2; j++ ) {
							var verticalIndex = i === indexh ? indexv : getPreviousVerticalIndex( hslide );

							var vslide = verticalSlides[j];

							vslide.setAttribute( 'data-index-h', i );
							vslide.setAttribute( 'data-index-v', j );

							// Apply CSS transform
							transformElement( vslide, 'translate(0%, ' + ( ( j - verticalIndex ) * 105 ) + '%)' );

							// Navigate to this slide on click
							vslide.addEventListener( 'click', onOverviewSlideClicked, true );
						}

					}
					else {

						// Navigate to this slide on click
						hslide.addEventListener( 'click', onOverviewSlideClicked, true );

					}
				}

				updateSlidesVisibility();

				layout();

				if( !wasActive ) {
					// Notify observers of the overview showing
					dispatchEvent( 'overviewshown', {
						'indexh': indexh,
						'indexv': indexv,
						'currentSlide': currentSlide
					} );
				}

			}, 10 );

		}

	}

	/**
	 * Exits the slide overview and enters the currently
	 * active slide.
	 */
	function deactivateOverview() {

		// Only proceed if enabled in config
		if( config.overview ) {

			clearTimeout( activateOverviewTimeout );
			clearTimeout( deactivateOverviewTimeout );

			dom.wrapper.classList.remove( 'overview' );

			// Temporarily add a class so that transitions can do different things
			// depending on whether they are exiting/entering overview, or just
			// moving from slide to slide
			dom.wrapper.classList.add( 'exit-overview' );

			deactivateOverviewTimeout = setTimeout( function () {
				dom.wrapper.classList.remove( 'exit-overview' );
			}, 10);

			// Select all slides
			var slides = toArray( document.querySelectorAll( SLIDES_SELECTOR ) );

			for( var i = 0, len = slides.length; i < len; i++ ) {
				var element = slides[i];

				element.style.display = '';

				// Resets all transforms to use the external styles
				transformElement( element, '' );

				element.removeEventListener( 'click', onOverviewSlideClicked, true );
			}

			slide( indexh, indexv );

			cueAutoSlide();

			// Notify observers of the overview hiding
			dispatchEvent( 'overviewhidden', {
				'indexh': indexh,
				'indexv': indexv,
				'currentSlide': currentSlide
			} );

		}
	}

	/**
	 * Toggles the slide overview mode on and off.
	 *
	 * @param {Boolean} override Optional flag which overrides the
	 * toggle logic and forcibly sets the desired state. True means
	 * overview is open, false means it's closed.
	 */
	function toggleOverview( override ) {

		if( typeof override === 'boolean' ) {
			override ? activateOverview() : deactivateOverview();
		}
		else {
			isOverview() ? deactivateOverview() : activateOverview();
		}

	}

	/**
	 * Checks if the overview is currently active.
	 *
	 * @return {Boolean} true if the overview is active,
	 * false otherwise
	 */
	function isOverview() {

		return dom.wrapper.classList.contains( 'overview' );

	}

	/**
	 * Checks if the current or specified slide is vertical
	 * (nested within another slide).
	 *
	 * @param {HTMLElement} slide [optional] The slide to check
	 * orientation of
	 */
	function isVerticalSlide( slide ) {

		// Prefer slide argument, otherwise use current slide
		slide = slide ? slide : currentSlide;

		return slide && !!slide.parentNode.nodeName.match( /section/i );

	}

	/**
	 * Handling the fullscreen functionality via the fullscreen API
	 *
	 * @see http://fullscreen.spec.whatwg.org/
	 * @see https://developer.mozilla.org/en-US/docs/DOM/Using_fullscreen_mode
	 */
	function enterFullscreen() {

		var element = document.body;

		// Check which implementation is available
		var requestMethod = element.requestFullScreen ||
							element.webkitRequestFullscreen ||
							element.webkitRequestFullScreen ||
							element.mozRequestFullScreen ||
							element.msRequestFullScreen;

		if( requestMethod ) {
			requestMethod.apply( element );
		}

	}

	/**
	 * Enters the paused mode which fades everything on screen to
	 * black.
	 */
	function pause() {

		var wasPaused = dom.wrapper.classList.contains( 'paused' );

		cancelAutoSlide();
		dom.wrapper.classList.add( 'paused' );

		if( wasPaused === false ) {
			dispatchEvent( 'paused' );
		}

	}

	/**
	 * Exits from the paused mode.
	 */
	function resume() {

		var wasPaused = dom.wrapper.classList.contains( 'paused' );
		dom.wrapper.classList.remove( 'paused' );

		cueAutoSlide();

		if( wasPaused ) {
			dispatchEvent( 'resumed' );
		}

	}

	/**
	 * Toggles the paused mode on and off.
	 */
	function togglePause() {

		if( isPaused() ) {
			resume();
		}
		else {
			pause();
		}

	}

	/**
	 * Checks if we are currently in the paused mode.
	 */
	function isPaused() {

		return dom.wrapper.classList.contains( 'paused' );

	}

	/**
	 * Steps from the current point in the presentation to the
	 * slide which matches the specified horizontal and vertical
	 * indices.
	 *
	 * @param {int} h Horizontal index of the target slide
	 * @param {int} v Vertical index of the target slide
	 * @param {int} f Optional index of a fragment within the
	 * target slide to activate
	 * @param {int} o Optional origin for use in multimaster environments
	 */
	function slide( h, v, f, o ) {

		// Remember where we were at before
		previousSlide = currentSlide;

		// Query all horizontal slides in the deck
		var horizontalSlides = document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR );

		// If no vertical index is specified and the upcoming slide is a
		// stack, resume at its previous vertical index
		if( v === undefined ) {
			v = getPreviousVerticalIndex( horizontalSlides[ h ] );
		}

		// If we were on a vertical stack, remember what vertical index
		// it was on so we can resume at the same position when returning
		if( previousSlide && previousSlide.parentNode && previousSlide.parentNode.classList.contains( 'stack' ) ) {
			setPreviousVerticalIndex( previousSlide.parentNode, indexv );
		}

		// Remember the state before this slide
		var stateBefore = state.concat();

		// Reset the state array
		state.length = 0;

		var indexhBefore = indexh || 0,
			indexvBefore = indexv || 0;

		// Activate and transition to the new slide
		indexh = updateSlides( HORIZONTAL_SLIDES_SELECTOR, h === undefined ? indexh : h );
		indexv = updateSlides( VERTICAL_SLIDES_SELECTOR, v === undefined ? indexv : v );

		// Update the visibility of slides now that the indices have changed
		updateSlidesVisibility();

		layout();

		// Apply the new state
		stateLoop: for( var i = 0, len = state.length; i < len; i++ ) {
			// Check if this state existed on the previous slide. If it
			// did, we will avoid adding it repeatedly
			for( var j = 0; j < stateBefore.length; j++ ) {
				if( stateBefore[j] === state[i] ) {
					stateBefore.splice( j, 1 );
					continue stateLoop;
				}
			}

			document.documentElement.classList.add( state[i] );

			// Dispatch custom event matching the state's name
			dispatchEvent( state[i] );
		}

		// Clean up the remains of the previous state
		while( stateBefore.length ) {
			document.documentElement.classList.remove( stateBefore.pop() );
		}

		// If the overview is active, re-activate it to update positions
		if( isOverview() ) {
			activateOverview();
		}

		// Find the current horizontal slide and any possible vertical slides
		// within it
		var currentHorizontalSlide = horizontalSlides[ indexh ],
			currentVerticalSlides = currentHorizontalSlide.querySelectorAll( 'section' );

		// Store references to the previous and current slides
		currentSlide = currentVerticalSlides[ indexv ] || currentHorizontalSlide;


		// Show fragment, if specified
		if( typeof f !== 'undefined' ) {
			var fragments = sortFragments( currentSlide.querySelectorAll( '.fragment' ) );

			toArray( fragments ).forEach( function( fragment, indexf ) {
				if( indexf < f ) {
					fragment.classList.add( 'visible' );
				}
				else {
					fragment.classList.remove( 'visible' );
				}
			} );
		}

		// Dispatch an event if the slide changed
		var slideChanged = ( indexh !== indexhBefore || indexv !== indexvBefore );
		if( slideChanged ) {
			dispatchEvent( 'slidechanged', {
				'indexh': indexh,
				'indexv': indexv,
				'previousSlide': previousSlide,
				'currentSlide': currentSlide,
				'origin': o
			} );
		}
		else {
			// Ensure that the previous slide is never the same as the current
			previousSlide = null;
		}

		// Solves an edge case where the previous slide maintains the
		// 'present' class when navigating between adjacent vertical
		// stacks
		if( previousSlide ) {
			previousSlide.classList.remove( 'present' );

			// Reset all slides upon navigate to home
			// Issue: #285
			if ( document.querySelector( HOME_SLIDE_SELECTOR ).classList.contains( 'present' ) ) {
				// Launch async task
				setTimeout( function () {
					var slides = toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.stack') ), i;
					for( i in slides ) {
						if( slides[i] ) {
							// Reset stack
							setPreviousVerticalIndex( slides[i], 0 );
						}
					}
				}, 0 );
			}
		}

		// Handle embedded content
		if( slideChanged ) {
			stopEmbeddedContent( previousSlide );
			startEmbeddedContent( currentSlide );
		}

		updateControls();
		updateProgress();
		updateBackground();

		// Update the URL hash
		writeURL();

	}

	/**
	 * Syncs the presentation with the current DOM. Useful
	 * when new slides or control elements are added or when
	 * the configuration has changed.
	 */
	function sync() {

		// Subscribe to input
		removeEventListeners();
		addEventListeners();

		// Force a layout to make sure the current config is accounted for
		layout();

		// Reflect the current autoSlide value
		autoSlide = config.autoSlide;

		// Start auto-sliding if it's enabled
		cueAutoSlide();

		// Re-create the slide backgrounds
		createBackgrounds();

		updateControls();
		updateProgress();
		updateBackground();

	}

	/**
	 * Updates one dimension of slides by showing the slide
	 * with the specified index.
	 *
	 * @param {String} selector A CSS selector that will fetch
	 * the group of slides we are working with
	 * @param {Number} index The index of the slide that should be
	 * shown
	 *
	 * @return {Number} The index of the slide that is now shown,
	 * might differ from the passed in index if it was out of
	 * bounds.
	 */
	function updateSlides( selector, index ) {

		// Select all slides and convert the NodeList result to
		// an array
		var slides = toArray( document.querySelectorAll( selector ) ),
			slidesLength = slides.length;

		if( slidesLength ) {

			// Should the index loop?
			if( config.loop ) {
				index %= slidesLength;

				if( index < 0 ) {
					index = slidesLength + index;
				}
			}

			// Enforce max and minimum index bounds
			index = Math.max( Math.min( index, slidesLength - 1 ), 0 );

			for( var i = 0; i < slidesLength; i++ ) {
				var element = slides[i];

				var reverse = config.rtl && !isVerticalSlide( element );

				element.classList.remove( 'past' );
				element.classList.remove( 'present' );
				element.classList.remove( 'future' );

				// http://www.w3.org/html/wg/drafts/html/master/editing.html#the-hidden-attribute
				element.setAttribute( 'hidden', '' );

				if( i < index ) {
					// Any element previous to index is given the 'past' class
					element.classList.add( reverse ? 'future' : 'past' );
				}
				else if( i > index ) {
					// Any element subsequent to index is given the 'future' class
					element.classList.add( reverse ? 'past' : 'future' );

					var fragments = toArray( element.querySelectorAll( '.fragment.visible' ) );

					// No fragments in future slides should be visible ahead of time
					while( fragments.length ) {
						fragments.pop().classList.remove( 'visible' );
					}
				}

				// If this element contains vertical slides
				if( element.querySelector( 'section' ) ) {
					element.classList.add( 'stack' );
				}
			}

			// Mark the current slide as present
			slides[index].classList.add( 'present' );
			slides[index].removeAttribute( 'hidden' );

			// If this slide has a state associated with it, add it
			// onto the current state of the deck
			var slideState = slides[index].getAttribute( 'data-state' );
			if( slideState ) {
				state = state.concat( slideState.split( ' ' ) );
			}

			// If this slide has a data-autoslide attribute associated use this as
			// autoSlide value otherwise use the global configured time
			var slideAutoSlide = slides[index].getAttribute( 'data-autoslide' );
			if( slideAutoSlide ) {
				autoSlide = parseInt( slideAutoSlide, 10 );
			}
			else {
				autoSlide = config.autoSlide;
			}

			cueAutoSlide();

		}
		else {
			// Since there are no slides we can't be anywhere beyond the
			// zeroth index
			index = 0;
		}

		return index;

	}

	/**
	 * Optimization method; hide all slides that are far away
	 * from the present slide.
	 */
	function updateSlidesVisibility() {

		// Select all slides and convert the NodeList result to
		// an array
		var horizontalSlides = toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ),
			horizontalSlidesLength = horizontalSlides.length,
			distanceX,
			distanceY;

		if( horizontalSlidesLength ) {

			// The number of steps away from the present slide that will
			// be visible
			var viewDistance = isOverview() ? 10 : config.viewDistance;

			// Limit view distance on weaker devices
			if( isMobileDevice ) {
				viewDistance = isOverview() ? 6 : 1;
			}

			for( var x = 0; x < horizontalSlidesLength; x++ ) {
				var horizontalSlide = horizontalSlides[x];

				var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) ),
					verticalSlidesLength = verticalSlides.length;

				// Loops so that it measures 1 between the first and last slides
				distanceX = Math.abs( ( indexh - x ) % ( horizontalSlidesLength - viewDistance ) ) || 0;

				// Show the horizontal slide if it's within the view distance
				horizontalSlide.style.display = distanceX > viewDistance ? 'none' : 'block';

				if( verticalSlidesLength ) {

					var oy = getPreviousVerticalIndex( horizontalSlide );

					for( var y = 0; y < verticalSlidesLength; y++ ) {
						var verticalSlide = verticalSlides[y];

						distanceY = x === indexh ? Math.abs( indexv - y ) : Math.abs( y - oy );

						verticalSlide.style.display = ( distanceX + distanceY ) > viewDistance ? 'none' : 'block';
					}

				}
			}

		}

	}

	/**
	 * Updates the progress bar to reflect the current slide.
	 */
	function updateProgress() {

		// Update progress if enabled
		if( config.progress && dom.progress ) {

			var horizontalSlides = toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

			// The number of past and total slides
			var totalCount = document.querySelectorAll( SLIDES_SELECTOR + ':not(.stack)' ).length;
			var pastCount = 0;

			// Step through all slides and count the past ones
			mainLoop: for( var i = 0; i < horizontalSlides.length; i++ ) {

				var horizontalSlide = horizontalSlides[i];
				var verticalSlides = toArray( horizontalSlide.querySelectorAll( 'section' ) );

				for( var j = 0; j < verticalSlides.length; j++ ) {

					// Stop as soon as we arrive at the present
					if( verticalSlides[j].classList.contains( 'present' ) ) {
						break mainLoop;
					}

					pastCount++;

				}

				// Stop as soon as we arrive at the present
				if( horizontalSlide.classList.contains( 'present' ) ) {
					break;
				}

				// Don't count the wrapping section for vertical slides
				if( horizontalSlide.classList.contains( 'stack' ) === false ) {
					pastCount++;
				}

			}

			dom.progressbar.style.width = ( pastCount / ( totalCount - 1 ) ) * window.innerWidth + 'px';

		}

	}

	/**
	 * Updates the state of all control/navigation arrows.
	 */
	function updateControls() {

		if ( config.controls && dom.controls ) {

			var routes = availableRoutes();
			var fragments = availableFragments();

			// Remove the 'enabled' class from all directions
			dom.controlsLeft.concat( dom.controlsRight )
							.concat( dom.controlsUp )
							.concat( dom.controlsDown )
							.concat( dom.controlsPrev )
							.concat( dom.controlsNext ).forEach( function( node ) {
				node.classList.remove( 'enabled' );
				node.classList.remove( 'fragmented' );
			} );

			// Add the 'enabled' class to the available routes
			if( routes.left ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'enabled' );	} );
			if( routes.right ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'enabled' ); } );
			if( routes.up ) dom.controlsUp.forEach( function( el ) { el.classList.add( 'enabled' );	} );
			if( routes.down ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'enabled' ); } );

			// Prev/next buttons
			if( routes.left || routes.up ) dom.controlsPrev.forEach( function( el ) { el.classList.add( 'enabled' ); } );
			if( routes.right || routes.down ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'enabled' ); } );

			// Highlight fragment directions
			if( currentSlide ) {

				// Always apply fragment decorator to prev/next buttons
				if( fragments.prev ) dom.controlsPrev.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
				if( fragments.next ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );

				// Apply fragment decorators to directional buttons based on
				// what slide axis they are in
				if( isVerticalSlide( currentSlide ) ) {
					if( fragments.prev ) dom.controlsUp.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
					if( fragments.next ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
				}
				else {
					if( fragments.prev ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
					if( fragments.next ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); } );
				}
			}

		}

	}

	/**
	 * Updates the background elements to reflect the current 
	 * slide.
	 */
	function updateBackground() {

		// Update the classes of all backgrounds to match the 
		// states of their slides (past/present/future)
		toArray( dom.background.childNodes ).forEach( function( backgroundh, h ) {

			// Reverse past/future classes when in RTL mode
			var horizontalPast = config.rtl ? 'future' : 'past',
				horizontalFuture = config.rtl ? 'past' : 'future';

			backgroundh.className = 'slide-background ' + ( h < indexh ? horizontalPast : h > indexh ? horizontalFuture : 'present' );

			toArray( backgroundh.childNodes ).forEach( function( backgroundv, v ) {

				backgroundv.className = 'slide-background ' + ( v < indexv ? 'past' : v > indexv ? 'future' : 'present' );

			} );

		} );

		// Allow the first background to apply without transition
		setTimeout( function() {
			dom.background.classList.remove( 'no-transition' );
		}, 1 );

	}

	/**
	 * Determine what available routes there are for navigation.
	 *
	 * @return {Object} containing four booleans: left/right/up/down
	 */
	function availableRoutes() {

		var horizontalSlides = document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ),
			verticalSlides = document.querySelectorAll( VERTICAL_SLIDES_SELECTOR );

		var routes = {
			left: indexh > 0 || config.loop,
			right: indexh < horizontalSlides.length - 1 || config.loop,
			up: indexv > 0,
			down: indexv < verticalSlides.length - 1
		};

		// reverse horizontal controls for rtl
		if( config.rtl ) {
			var left = routes.left;
			routes.left = routes.right;
			routes.right = left;
		}

		return routes;

	}

	/**
	 * Returns an object describing the available fragment
	 * directions.
	 *
	 * @return {Object} two boolean properties: prev/next
	 */
	function availableFragments() {

		if( currentSlide && config.fragments ) {
			var fragments = currentSlide.querySelectorAll( '.fragment' );
			var hiddenFragments = currentSlide.querySelectorAll( '.fragment:not(.visible)' );

			return {
				prev: fragments.length - hiddenFragments.length > 0,
				next: !!hiddenFragments.length
			};
		}
		else {
			return { prev: false, next: false };
		}

	}

	/**
	 * Start playback of any embedded content inside of
	 * the targeted slide.
	 */
	function startEmbeddedContent( slide ) {

		if( slide ) {
			// HTML5 media elements
			toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
				if( el.hasAttribute( 'data-autoplay' ) ) {
					el.play();
				}
			} );

			// YouTube embeds
			toArray( slide.querySelectorAll( 'iframe[src*="youtube.com/embed/"]' ) ).forEach( function( el ) {
				if( el.hasAttribute( 'data-autoplay' ) ) {
					el.contentWindow.postMessage('{"event":"command","func":"playVideo","args":""}', '*');
				}
			});
		}

	}

	/**
	 * Stop playback of any embedded content inside of
	 * the targeted slide.
	 */
	function stopEmbeddedContent( slide ) {

		if( slide ) {
			// HTML5 media elements
			toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
				if( !el.hasAttribute( 'data-ignore' ) ) {
					el.pause();
				}
			} );

			// YouTube embeds
			toArray( slide.querySelectorAll( 'iframe[src*="youtube.com/embed/"]' ) ).forEach( function( el ) {
				if( !el.hasAttribute( 'data-ignore' ) && typeof el.contentWindow.postMessage === 'function' ) {
					el.contentWindow.postMessage('{"event":"command","func":"pauseVideo","args":""}', '*');
				}
			});
		}

	}

	/**
	 * Reads the current URL (hash) and navigates accordingly.
	 */
	function readURL() {

		var hash = window.location.hash;

		// Attempt to parse the hash as either an index or name
		var bits = hash.slice( 2 ).split( '/' ),
			name = hash.replace( /#|\//gi, '' );

		// If the first bit is invalid and there is a name we can
		// assume that this is a named link
		if( isNaN( parseInt( bits[0], 10 ) ) && name.length ) {
			// Find the slide with the specified name
			var element = document.querySelector( '#' + name );

			if( element ) {
				// Find the position of the named slide and navigate to it
				var indices = Reveal.getIndices( element );
				slide( indices.h, indices.v );
			}
			// If the slide doesn't exist, navigate to the current slide
			else {
				slide( indexh || 0, indexv || 0 );
			}
		}
		else {
			// Read the index components of the hash
			var h = parseInt( bits[0], 10 ) || 0,
				v = parseInt( bits[1], 10 ) || 0;

			if( h !== indexh || v !== indexv ) {
				slide( h, v );
			}
		}

	}

	/**
	 * Updates the page URL (hash) to reflect the current
	 * state.
	 *
	 * @param {Number} delay The time in ms to wait before
	 * writing the hash
	 */
	function writeURL( delay ) {

		if( config.history ) {

			// Make sure there's never more than one timeout running
			clearTimeout( writeURLTimeout );

			// If a delay is specified, timeout this call
			if( typeof delay === 'number' ) {
				writeURLTimeout = setTimeout( writeURL, delay );
			}
			else {
				var url = '/';

				// If the current slide has an ID, use that as a named link
				if( currentSlide && typeof currentSlide.getAttribute( 'id' ) === 'string' ) {
					url = '/' + currentSlide.getAttribute( 'id' );
				}
				// Otherwise use the /h/v index
				else {
					if( indexh > 0 || indexv > 0 ) url += indexh;
					if( indexv > 0 ) url += '/' + indexv;
				}

				window.location.hash = url;
			}
		}

	}

	/**
	 * Retrieves the h/v location of the current, or specified,
	 * slide.
	 *
	 * @param {HTMLElement} slide If specified, the returned
	 * index will be for this slide rather than the currently
	 * active one
	 *
	 * @return {Object} { h: <int>, v: <int>, f: <int> }
	 */
	function getIndices( slide ) {

		// By default, return the current indices
		var h = indexh,
			v = indexv,
			f;

		// If a slide is specified, return the indices of that slide
		if( slide ) {
			var isVertical = isVerticalSlide( slide );
			var slideh = isVertical ? slide.parentNode : slide;

			// Select all horizontal slides
			var horizontalSlides = toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

			// Now that we know which the horizontal slide is, get its index
			h = Math.max( horizontalSlides.indexOf( slideh ), 0 );

			// If this is a vertical slide, grab the vertical index
			if( isVertical ) {
				v = Math.max( toArray( slide.parentNode.querySelectorAll( 'section' ) ).indexOf( slide ), 0 );
			}
		}

		if( !slide && currentSlide ) {
			var hasFragments = currentSlide.querySelectorAll( '.fragment' ).length > 0;
			if( hasFragments ) {
				var visibleFragments = currentSlide.querySelectorAll( '.fragment.visible' );
				f = visibleFragments.length;
			}
		}

		return { h: h, v: v, f: f };

	}

	/**
	 * Navigate to the next slide fragment.
	 *
	 * @return {Boolean} true if there was a next fragment,
	 * false otherwise
	 */
	function nextFragment() {

		if( currentSlide && config.fragments ) {
			var fragments = sortFragments( currentSlide.querySelectorAll( '.fragment:not(.visible)' ) );

			if( fragments.length ) {
				// Find the index of the next fragment
				var index = fragments[0].getAttribute( 'data-fragment-index' );

				// Find all fragments with the same index
				fragments = currentSlide.querySelectorAll( '.fragment[data-fragment-index="'+ index +'"]' );

				toArray( fragments ).forEach( function( element ) {
					element.classList.add( 'visible' );
				} );

				// Notify subscribers of the change
				dispatchEvent( 'fragmentshown', { fragment: fragments[0], fragments: fragments } );

				updateControls();
				return true;
			}
		}

		return false;

	}

	/**
	 * Navigate to the previous slide fragment.
	 *
	 * @return {Boolean} true if there was a previous fragment,
	 * false otherwise
	 */
	function previousFragment() {

		if( currentSlide && config.fragments ) {
			var fragments = sortFragments( currentSlide.querySelectorAll( '.fragment.visible' ) );

			if( fragments.length ) {
				// Find the index of the previous fragment
				var index = fragments[ fragments.length - 1 ].getAttribute( 'data-fragment-index' );

				// Find all fragments with the same index
				fragments = currentSlide.querySelectorAll( '.fragment[data-fragment-index="'+ index +'"]' );

				toArray( fragments ).forEach( function( f ) {
					f.classList.remove( 'visible' );
				} );

				// Notify subscribers of the change
				dispatchEvent( 'fragmenthidden', { fragment: fragments[0], fragments: fragments } );

				updateControls();
				return true;
			}
		}

		return false;

	}

	/**
	 * Cues a new automated slide if enabled in the config.
	 */
	function cueAutoSlide() {

		clearTimeout( autoSlideTimeout );

		// Cue the next auto-slide if enabled
		if( autoSlide && !isPaused() && !isOverview() ) {
			autoSlideTimeout = setTimeout( navigateNext, autoSlide );
		}

	}

	/**
	 * Cancels any ongoing request to auto-slide.
	 */
	function cancelAutoSlide() {

		clearTimeout( autoSlideTimeout );

	}

	function navigateLeft() {

		// Reverse for RTL
		if( config.rtl ) {
			if( ( isOverview() || nextFragment() === false ) && availableRoutes().left ) {
				slide( indexh + 1 );
			}
		}
		// Normal navigation
		else if( ( isOverview() || previousFragment() === false ) && availableRoutes().left ) {
			slide( indexh - 1 );
		}

	}

	function navigateRight() {

		// Reverse for RTL
		if( config.rtl ) {
			if( ( isOverview() || previousFragment() === false ) && availableRoutes().right ) {
				slide( indexh - 1 );
			}
		}
		// Normal navigation
		else if( ( isOverview() || nextFragment() === false ) && availableRoutes().right ) {
			slide( indexh + 1 );
		}

	}

	function navigateUp() {

		// Prioritize hiding fragments
		if( ( isOverview() || previousFragment() === false ) && availableRoutes().up ) {
			slide( indexh, indexv - 1 );
		}

	}

	function navigateDown() {

		// Prioritize revealing fragments
		if( ( isOverview() || nextFragment() === false ) && availableRoutes().down ) {
			slide( indexh, indexv + 1 );
		}

	}

	/**
	 * Navigates backwards, prioritized in the following order:
	 * 1) Previous fragment
	 * 2) Previous vertical slide
	 * 3) Previous horizontal slide
	 */
	function navigatePrev() {

		// Prioritize revealing fragments
		if( previousFragment() === false ) {
			if( availableRoutes().up ) {
				navigateUp();
			}
			else {
				// Fetch the previous horizontal slide, if there is one
				var previousSlide = document.querySelector( HORIZONTAL_SLIDES_SELECTOR + '.past:nth-child(' + indexh + ')' );

				if( previousSlide ) {
					var v = ( previousSlide.querySelectorAll( 'section' ).length - 1 ) || undefined;
					var h = indexh - 1;
					slide( h, v );
				}
			}
		}

	}

	/**
	 * Same as #navigatePrev() but navigates forwards.
	 */
	function navigateNext() {

		// Prioritize revealing fragments
		if( nextFragment() === false ) {
			availableRoutes().down ? navigateDown() : navigateRight();
		}

		// If auto-sliding is enabled we need to cue up
		// another timeout
		cueAutoSlide();

	}


	// --------------------------------------------------------------------//
	// ----------------------------- EVENTS -------------------------------//
	// --------------------------------------------------------------------//


	/**
	 * Handler for the document level 'keydown' event.
	 *
	 * @param {Object} event
	 */
	function onDocumentKeyDown( event ) {

		// Check if there's a focused element that could be using
		// the keyboard
		var activeElement = document.activeElement;
		var hasFocus = !!( document.activeElement && ( document.activeElement.type || document.activeElement.href || document.activeElement.contentEditable !== 'inherit' ) );

		// Disregard the event if there's a focused element or a
		// keyboard modifier key is present
		if( hasFocus || (event.shiftKey && event.keyCode !== 32) || event.altKey || event.ctrlKey || event.metaKey ) return;

		// While paused only allow "unpausing" keyboard events (b and .)
		if( isPaused() && [66,190,191].indexOf( event.keyCode ) === -1 ) {
			return false;
		}

		var triggered = false;

		// 1. User defined key bindings
		if( typeof config.keyboard === 'object' ) {

			for( var key in config.keyboard ) {

				// Check if this binding matches the pressed key
				if( parseInt( key, 10 ) === event.keyCode ) {

					var value = config.keyboard[ key ];

					// Callback function
					if( typeof value === 'function' ) {
						value.apply( null, [ event ] );
					}
					// String shortcuts to reveal.js API
					else if( typeof value === 'string' && typeof Reveal[ value ] === 'function' ) {
						Reveal[ value ].call();
					}

					triggered = true;

				}

			}

		}

		// 2. System defined key bindings
		if( triggered === false ) {

			// Assume true and try to prove false
			triggered = true;

			switch( event.keyCode ) {
				// p, page up
				case 80: case 33: navigatePrev(); break;
				// n, page down
				case 78: case 34: navigateNext(); break;
				// h, left
				case 72: case 37: navigateLeft(); break;
				// l, right
				case 76: case 39: navigateRight(); break;
				// k, up
				case 75: case 38: navigateUp(); break;
				// j, down
				case 74: case 40: navigateDown(); break;
				// home
				case 36: slide( 0 ); break;
				// end
				case 35: slide( Number.MAX_VALUE ); break;
				// space
				case 32: isOverview() ? deactivateOverview() : event.shiftKey ? navigatePrev() : navigateNext(); break;
				// return
				case 13: isOverview() ? deactivateOverview() : triggered = false; break;
				// b, period, Logitech presenter tools "black screen" button
				case 66: case 190: case 191: togglePause(); break;
				// f
				case 70: enterFullscreen(); break;
				default:
					triggered = false;
			}

		}

		// If the input resulted in a triggered action we should prevent
		// the browsers default behavior
		if( triggered ) {
			event.preventDefault();
		}
		// ESC or O key
		else if ( ( event.keyCode === 27 || event.keyCode === 79 ) && supports3DTransforms ) {
			toggleOverview();

			event.preventDefault();
		}

		// If auto-sliding is enabled we need to cue up
		// another timeout
		cueAutoSlide();

	}

	/**
	 * Handler for the 'touchstart' event, enables support for
	 * swipe and pinch gestures.
	 */
	function onTouchStart( event ) {

		touch.startX = event.touches[0].clientX;
		touch.startY = event.touches[0].clientY;
		touch.startCount = event.touches.length;

		// If there's two touches we need to memorize the distance
		// between those two points to detect pinching
		if( event.touches.length === 2 && config.overview ) {
			touch.startSpan = distanceBetween( {
				x: event.touches[1].clientX,
				y: event.touches[1].clientY
			}, {
				x: touch.startX,
				y: touch.startY
			} );
		}

	}

	/**
	 * Handler for the 'touchmove' event.
	 */
	function onTouchMove( event ) {

		// Each touch should only trigger one action
		if( !touch.captured ) {
			var currentX = event.touches[0].clientX;
			var currentY = event.touches[0].clientY;

			// If the touch started with two points and still has
			// two active touches; test for the pinch gesture
			if( event.touches.length === 2 && touch.startCount === 2 && config.overview ) {

				// The current distance in pixels between the two touch points
				var currentSpan = distanceBetween( {
					x: event.touches[1].clientX,
					y: event.touches[1].clientY
				}, {
					x: touch.startX,
					y: touch.startY
				} );

				// If the span is larger than the desire amount we've got
				// ourselves a pinch
				if( Math.abs( touch.startSpan - currentSpan ) > touch.threshold ) {
					touch.captured = true;

					if( currentSpan < touch.startSpan ) {
						activateOverview();
					}
					else {
						deactivateOverview();
					}
				}

				event.preventDefault();

			}
			// There was only one touch point, look for a swipe
			else if( event.touches.length === 1 && touch.startCount !== 2 ) {

				var deltaX = currentX - touch.startX,
					deltaY = currentY - touch.startY;

				if( deltaX > touch.threshold && Math.abs( deltaX ) > Math.abs( deltaY ) ) {
					touch.captured = true;
					navigateLeft();
				}
				else if( deltaX < -touch.threshold && Math.abs( deltaX ) > Math.abs( deltaY ) ) {
					touch.captured = true;
					navigateRight();
				}
				else if( deltaY > touch.threshold ) {
					touch.captured = true;
					navigateUp();
				}
				else if( deltaY < -touch.threshold ) {
					touch.captured = true;
					navigateDown();
				}

				// If we're embedded, only block touch events if they have
				// triggered an action
				if( config.embedded ) {
					if( touch.captured || isVerticalSlide( currentSlide ) ) {
						event.preventDefault();
					}
				}
				// Not embedded? Block them all to avoid needless tossing
				// around of the viewport in iOS
				else {
					event.preventDefault();
				}

			}
		}
		// There's a bug with swiping on some Android devices unless
		// the default action is always prevented
		else if( navigator.userAgent.match( /android/gi ) ) {
			event.preventDefault();
		}

	}

	/**
	 * Handler for the 'touchend' event.
	 */
	function onTouchEnd( event ) {

		touch.captured = false;

	}

	/**
	 * Convert pointer down to touch start.
	 */
	function onPointerDown( event ) {

		if( event.pointerType === event.MSPOINTER_TYPE_TOUCH ) {
			event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
			onTouchStart( event );
		}

	}

	/**
	 * Convert pointer move to touch move.
	 */
	function onPointerMove( event ) {

		if( event.pointerType === event.MSPOINTER_TYPE_TOUCH ) {
			event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
			onTouchMove( event );
		}

	}

	/**
	 * Convert pointer up to touch end.
	 */
	function onPointerUp( event ) {

		if( event.pointerType === event.MSPOINTER_TYPE_TOUCH ) {
			event.touches = [{ clientX: event.clientX, clientY: event.clientY }];
			onTouchEnd( event );
		}

	}

	/**
	 * Handles mouse wheel scrolling, throttled to avoid skipping
	 * multiple slides.
	 */
	function onDocumentMouseScroll( event ) {

		if( Date.now() - lastMouseWheelStep > 600 ) {

			lastMouseWheelStep = Date.now();

			var delta = event.detail || -event.wheelDelta;
			if( delta > 0 ) {
				navigateNext();
			}
			else {
				navigatePrev();
			}

		}

	}

	/**
	 * Clicking on the progress bar results in a navigation to the
	 * closest approximate horizontal slide using this equation:
	 *
	 * ( clickX / presentationWidth ) * numberOfSlides
	 */
	function onProgressClicked( event ) {

		event.preventDefault();

		var slidesTotal = toArray( document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).length;
		var slideIndex = Math.floor( ( event.clientX / dom.wrapper.offsetWidth ) * slidesTotal );

		slide( slideIndex );

	}

	/**
	 * Event handler for navigation control buttons.
	 */
	function onNavigateLeftClicked( event ) { event.preventDefault(); navigateLeft(); }
	function onNavigateRightClicked( event ) { event.preventDefault(); navigateRight(); }
	function onNavigateUpClicked( event ) { event.preventDefault(); navigateUp(); }
	function onNavigateDownClicked( event ) { event.preventDefault(); navigateDown(); }
	function onNavigatePrevClicked( event ) { event.preventDefault(); navigatePrev(); }
	function onNavigateNextClicked( event ) { event.preventDefault(); navigateNext(); }

	/**
	 * Handler for the window level 'hashchange' event.
	 */
	function onWindowHashChange( event ) {

		readURL();

	}

	/**
	 * Handler for the window level 'resize' event.
	 */
	function onWindowResize( event ) {

		layout();

	}

	/**
	 * Invoked when a slide is and we're in the overview.
	 */
	function onOverviewSlideClicked( event ) {

		// TODO There's a bug here where the event listeners are not
		// removed after deactivating the overview.
		if( eventsAreBound && isOverview() ) {
			event.preventDefault();

			var element = event.target;

			while( element && !element.nodeName.match( /section/gi ) ) {
				element = element.parentNode;
			}

			if( element && !element.classList.contains( 'disabled' ) ) {

				deactivateOverview();

				if( element.nodeName.match( /section/gi ) ) {
					var h = parseInt( element.getAttribute( 'data-index-h' ), 10 ),
						v = parseInt( element.getAttribute( 'data-index-v' ), 10 );

					slide( h, v );
				}

			}
		}

	}

	/**
	 * Handles clicks on links that are set to preview in the
	 * iframe overlay.
	 */
	function onPreviewLinkClicked( event ) {

		var url = event.target.getAttribute( 'href' );
		if( url ) {
			openPreview( url );
			event.preventDefault();
		}

	}


	// --------------------------------------------------------------------//
	// ------------------------------- API --------------------------------//
	// --------------------------------------------------------------------//


	return {
		initialize: initialize,
		configure: configure,
		sync: sync,

		// Navigation methods
		slide: slide,
		left: navigateLeft,
		right: navigateRight,
		up: navigateUp,
		down: navigateDown,
		prev: navigatePrev,
		next: navigateNext,
		prevFragment: previousFragment,
		nextFragment: nextFragment,

		// Deprecated aliases
		navigateTo: slide,
		navigateLeft: navigateLeft,
		navigateRight: navigateRight,
		navigateUp: navigateUp,
		navigateDown: navigateDown,
		navigatePrev: navigatePrev,
		navigateNext: navigateNext,

		// Forces an update in slide layout
		layout: layout,

		// Returns an object with the available routes as booleans (left/right/top/bottom)
		availableRoutes: availableRoutes,

		// Returns an object with the available fragments as booleans (prev/next)
		availableFragments: availableFragments,

		// Toggles the overview mode on/off
		toggleOverview: toggleOverview,

		// Toggles the "black screen" mode on/off
		togglePause: togglePause,

		// State checks
		isOverview: isOverview,
		isPaused: isPaused,

		// Adds or removes all internal event listeners (such as keyboard)
		addEventListeners: addEventListeners,
		removeEventListeners: removeEventListeners,

		// Returns the indices of the current, or specified, slide
		getIndices: getIndices,

		// Returns the slide at the specified index, y is optional
		getSlide: function( x, y ) {
			var horizontalSlide = document.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR )[ x ];
			var verticalSlides = horizontalSlide && horizontalSlide.querySelectorAll( 'section' );

			if( typeof y !== 'undefined' ) {
				return verticalSlides ? verticalSlides[ y ] : undefined;
			}

			return horizontalSlide;
		},

		// Returns the previous slide element, may be null
		getPreviousSlide: function() {
			return previousSlide;
		},

		// Returns the current slide element
		getCurrentSlide: function() {
			return currentSlide;
		},

		// Returns the current scale of the presentation content
		getScale: function() {
			return scale;
		},

		// Returns the current configuration object
		getConfig: function() {
			return config;
		},

		// Helper method, retrieves query string as a key/value hash
		getQueryHash: function() {
			var query = {};

			location.search.replace( /[A-Z0-9]+?=(\w*)/gi, function(a) {
				query[ a.split( '=' ).shift() ] = a.split( '=' ).pop();
			} );

			return query;
		},

		// Returns true if we're currently on the first slide
		isFirstSlide: function() {
			return document.querySelector( SLIDES_SELECTOR + '.past' ) == null ? true : false;
		},

		// Returns true if we're currently on the last slide
		isLastSlide: function() {
			if( currentSlide && currentSlide.classList.contains( '.stack' ) ) {
				return currentSlide.querySelector( SLIDES_SELECTOR + '.future' ) == null ? true : false;
			}
			else {
				return document.querySelector( SLIDES_SELECTOR + '.future' ) == null ? true : false;
			}
		},

		// Checks if reveal.js has been loaded and is ready for use
		isReady: function() {
			return loaded;
		},

		// Forward event binding to the reveal DOM element
		addEventListener: function( type, listener, useCapture ) {
			if( 'addEventListener' in window ) {
				( dom.wrapper || document.querySelector( '.reveal' ) ).addEventListener( type, listener, useCapture );
			}
		},
		removeEventListener: function( type, listener, useCapture ) {
			if( 'addEventListener' in window ) {
				( dom.wrapper || document.querySelector( '.reveal' ) ).removeEventListener( type, listener, useCapture );
			}
		}
	};

})();