/*!
 * reveal.js
 * http://lab.hakim.se/reveal-js
 * MIT licensed
 *
 * Copyright (C) 2015 Hakim El Hattab, http://hakim.se
 */
(function( root, factory ) {
    if( typeof define === 'function' && define.amd ) {
        // AMD. Register as an anonymous module.
        define( function() {
            root.Reveal = factory();
            return root.Reveal;
        } );
    } else if( typeof exports === 'object' ) {
        // Node. Does not work with strict CommonJS.
        module.exports = factory();
    } else {
        // Browser globals.
        root.Reveal = factory();
    }
}( this, function() {

    'use strict';

    var Reveal;

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

    // 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,

            // Top and Left margins to reposition the slides
            marginTop: '',
            marginLeft: '',

            // Bounds for smallest/largest possible scale to apply to content
            minScale: 0.2,
            maxScale: 1.5,

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

            // Display a presentation progress bar
            progress: true,

            // Display the page number of the current slide
            slideNumber: false,

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

            // Enable keyboard shortcuts for navigation
            keyboard: true,

            // Optional function that blocks keyboard events when retuning false
            keyboardCondition: null,

            // Enable the slide overview mode
            overview: true,

            // Vertical centering 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,

            // Flags if we should show a help overlay when the questionmark
            // key is pressed
            help: true,

            // Flags if it should be possible to pause the presentation (blackout)
            pause: true,

            // 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,

            // Stop auto-sliding after user input
            autoSlideStoppable: true,

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

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

            // Hides the address bar on mobile devices
            hideAddressBar: true,

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

            // Exposes the reveal.js API through window.postMessage
            postMessage: true,

            // Dispatches all reveal.js events to the parent window through postMessage
            postMessageEvents: false,

            // Focuses body when page changes visiblity to ensure keyboard shortcuts work
            focusBodyOnPageVisibilityChange: true,

            // Transition style
            transition: 'slide', // none/fade/slide/convex/concave/zoom

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

            // Transition style for full page slide backgrounds
            backgroundTransition: 'fade', // none/fade/slide/convex/concave/zoom

            // Parallax background image
            parallaxBackgroundImage: '', // CSS syntax, e.g. "a.jpg"

            // Parallax background size
            parallaxBackgroundSize: '', // CSS syntax, e.g. "3000px 2000px"

            // Amount of pixels to move the parallax background per slide step
            parallaxBackgroundHorizontal: null,
            parallaxBackgroundVertical: null,

            // 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,

    // Flags if the overview mode is currently active
        overview = false,

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

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

        previousBackground,

    // 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,

    // CSS transform that is currently applied to the slides container,
    // split into two groups
        slidesTransform = { layout: '', overview: '' },

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

    // Features supported by the browser, see #checkCapabilities()
        features = {},

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

    // Throttles mouse wheel navigation
        lastMouseWheelStep = 0,

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

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

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

    // Auto slide properties
        autoSlidePlayer,
        autoSlideTimeout = 0,
        autoSlideStartTime = -1,
        autoSlidePaused = false,

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

    // Holds information about the keyboard shortcuts
        keyboardShortcuts = {
            'N  ,  SPACE':			'Next slide',
            'P':					'Previous slide',
            '←  ,  H':		'Navigate left',
            '→  ,  L':		'Navigate right',
            '↑  ,  K':		'Navigate up',
            '↓  ,  J':		'Navigate down',
            'Home':					'First slide',
            'End':					'Last slide',
            'B  ,  .':				'Pause',
            'F':					'Fullscreen',
            'ESC, O':				'Slide overview'
        };

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

        checkCapabilities();

        if( !features.transforms2d && !features.transforms3d ) {
            document.body.setAttribute( 'class', 'no-transforms' );

            // Since JS won't be running any further, we need to load all
            // images that were intended to lazy load now
            var images = document.getElementsByTagName( 'img' );
            for( var i = 0, len = images.length; i < len; i++ ) {
                var image = images[i];
                if( image.getAttribute( 'data-src' ) ) {
                    image.setAttribute( 'src', image.getAttribute( 'data-src' ) );
                    image.removeAttribute( 'data-src' );
                }
            }

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

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

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

        var query = Reveal.getQueryHash();

        // Do not accept new dependencies via query config to avoid
        // the potential of malicious script injection
        if( typeof query['dependencies'] !== 'undefined' ) delete query['dependencies'];

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

        // 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() {

        features.transforms3d = '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;

        features.transforms2d = '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;

        features.requestAnimationFrameMethod = window.requestAnimationFrame || window.webkitRequestAnimationFrame || window.mozRequestAnimationFrame;
        features.requestAnimationFrame = typeof features.requestAnimationFrameMethod === 'function';

        features.canvas = !!document.createElement( 'canvas' ).getContext;

        features.touch = !!( 'ontouchstart' in window );

        // Transitions in the overview are disabled in desktop and
        // mobile Safari due to lag
        features.overviewTransitions = !/Version\/[\d\.]+.*Safari/.test( navigator.userAgent );

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

    }

    /**
     * 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 = [],
            scriptsToPreload = 0;

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

            start();
        }

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

                if( --scriptsToPreload === 0 ) {
                    proceed();
                }
            });
        }

        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 );
                }

                loadScript( s );
            }
        }

        if( scripts.length ) {
            scriptsToPreload = scripts.length;

            // 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();

        // Listen to messages posted to this window
        setupPostMessage();

        // Prevent iframes from scrolling the slides out of view
        setupIframeScrollPrevention();

        // Resets all vertical slides so that only the first is visible
        resetVerticalSlides();

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

        // Read the initial hash
        readURL();

        // Update all backgrounds
        updateBackground( true );

        // 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 );

        // Special setup and config is required when printing to PDF
        if( isPrintingPDF() ) {
            removeEventListeners();

            // The document needs to have loaded for the PDF layout
            // measurements to be accurate
            if( document.readyState === 'complete' ) {
                setupPDF();
            }
            else {
                window.addEventListener( 'load', setupPDF );
            }
        }

    }

    /**
     * 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() {

        // 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>' );

        // Slide number
        dom.slideNumber = createSingletonNode( dom.wrapper, 'div', 'slide-number', '' );

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

        // Cache references to elements
        dom.controls = document.querySelector( '.reveal .controls' );
        dom.theme = document.querySelector( '#theme' );

        dom.wrapper.setAttribute( 'role', 'application' );

        // 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' ) );

        dom.statusDiv = createStatusDiv();
    }

    /**
     * Creates a hidden div with role aria-live to announce the
     * current slide content. Hide the div off-screen to make it
     * available only to Assistive Technologies.
     */
    function createStatusDiv() {

        var statusDiv = document.getElementById( 'aria-status-div' );
        if( !statusDiv ) {
            statusDiv = document.createElement( 'div' );
            statusDiv.style.position = 'absolute';
            statusDiv.style.height = '1px';
            statusDiv.style.width = '1px';
            statusDiv.style.overflow ='hidden';
            statusDiv.style.clip = 'rect( 1px, 1px, 1px, 1px )';
            statusDiv.setAttribute( 'id', 'aria-status-div' );
            statusDiv.setAttribute( 'aria-live', 'polite' );
            statusDiv.setAttribute( 'aria-atomic','true' );
            dom.wrapper.appendChild( statusDiv );
        }
        return statusDiv;

    }

    /**
     * Configures the presentation for printing to a static
     * PDF.
     */
    function setupPDF() {

        var slideSize = getComputedSlideSize( window.innerWidth, window.innerHeight );

        // Dimensions of the PDF pages
        var pageWidth = Math.floor( slideSize.width * ( 1 + config.margin ) ),
            pageHeight = Math.floor( slideSize.height * ( 1 + config.margin  ) );

        // Dimensions of slides within the pages
        var slideWidth = slideSize.width,
            slideHeight = slideSize.height;

        // Let the browser know what page size we want to print
        injectStyleSheet( '@page{size:'+ pageWidth +'px '+ pageHeight +'px; margin: 0;}' );

        // Limit the size of certain elements to the dimensions of the slide
        injectStyleSheet( '.reveal section>img, .reveal section>video, .reveal section>iframe{max-width: '+ slideWidth +'px; max-height:'+ slideHeight +'px}' );

        document.body.classList.add( 'print-pdf' );
        document.body.style.width = pageWidth + 'px';
        document.body.style.height = pageHeight + 'px';

        // Slide and slide background layout
        toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {

            // Vertical stacks are not centred since their section
            // children will be
            if( slide.classList.contains( 'stack' ) === false ) {
                // Center the slide inside of the page, giving the slide some margin
                var left = ( pageWidth - slideWidth ) / 2,
                    top = ( pageHeight - slideHeight ) / 2;

                var contentHeight = getAbsoluteHeight( slide );
                var numberOfPages = Math.max( Math.ceil( contentHeight / pageHeight ), 1 );

                // Center slides vertically
                if( numberOfPages === 1 && config.center || slide.classList.contains( 'center' ) ) {
                    top = Math.max( ( pageHeight - contentHeight ) / 2, 0 );
                }

                // Position the slide inside of the page
                slide.style.left = left + 'px';
                slide.style.top = top + 'px';
                slide.style.width = slideWidth + 'px';

                // TODO Backgrounds need to be multiplied when the slide
                // stretches over multiple pages
                var background = slide.querySelector( '.slide-background' );
                if( background ) {
                    background.style.width = pageWidth + 'px';
                    background.style.height = ( pageHeight * numberOfPages ) + 'px';
                    background.style.top = -top + 'px';
                    background.style.left = -left + 'px';
                }
            }

        } );

        // Show all fragments
        toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ' .fragment' ) ).forEach( function( fragment ) {
            fragment.classList.add( 'visible' );
        } );

    }

    /**
     * This is an unfortunate necessity. Iframes can trigger the
     * parent window to scroll, for example by focusing an input.
     * This scrolling can not be prevented by hiding overflow in
     * CSS so we have to resort to repeatedly checking if the
     * browser has decided to offset our slides :(
     */
    function setupIframeScrollPrevention() {

        if( dom.slides.querySelector( 'iframe' ) ) {
            setInterval( function() {
                if( dom.wrapper.scrollTop !== 0 || dom.wrapper.scrollLeft !== 0 ) {
                    dom.wrapper.scrollTop = 0;
                    dom.wrapper.scrollLeft = 0;
                }
            }, 500 );
        }

    }

    /**
     * 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 ) {

        // Find all nodes matching the description
        var nodes = container.querySelectorAll( '.' + classname );

        // Check all matches to find one which is a direct child of
        // the specified container
        for( var i = 0; i < nodes.length; i++ ) {
            var testNode = nodes[i];
            if( testNode.parentNode === container ) {
                return testNode;
            }
        }

        // If no node was found, create it now
        var node = document.createElement( tagname );
        node.classList.add( classname );
        if( typeof innerHTML === 'string' ) {
            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() {

        var printMode = isPrintingPDF();

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

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

            var backgroundStack;

            if( printMode ) {
                backgroundStack = createBackground( slideh, slideh );
            }
            else {
                backgroundStack = createBackground( slideh, dom.background );
            }

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

                if( printMode ) {
                    createBackground( slidev, slidev );
                }
                else {
                    createBackground( slidev, backgroundStack );
                }

                backgroundStack.classList.add( 'stack' );

            } );

        } );

        // Add parallax background if specified
        if( config.parallaxBackgroundImage ) {

            dom.background.style.backgroundImage = 'url("' + config.parallaxBackgroundImage + '")';
            dom.background.style.backgroundSize = config.parallaxBackgroundSize;

            // Make sure the below properties are set on the element - these properties are
            // needed for proper transitions to be set on the element via CSS. To remove
            // annoying background slide-in effect when the presentation starts, apply
            // these properties after short time delay
            setTimeout( function() {
                dom.wrapper.classList.add( 'has-parallax-background' );
            }, 1 );

        }
        else {

            dom.background.style.backgroundImage = '';
            dom.wrapper.classList.remove( 'has-parallax-background' );

        }

    }

    /**
     * Creates a background for the given slide.
     *
     * @param {HTMLElement} slide
     * @param {HTMLElement} container The element that the background
     * should be appended to
     */
    function createBackground( slide, container ) {

        var data = {
            background: slide.getAttribute( 'data-background' ),
            backgroundSize: slide.getAttribute( 'data-background-size' ),
            backgroundImage: slide.getAttribute( 'data-background-image' ),
            backgroundVideo: slide.getAttribute( 'data-background-video' ),
            backgroundIframe: slide.getAttribute( 'data-background-iframe' ),
            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' );

        // Carry over custom classes from the slide to the background
        element.className = 'slide-background ' + slide.className.replace( /present|past|future/, '' );

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

        // Create a hash for this combination of background settings.
        // This is used to determine when two slide backgrounds are
        // the same.
        if( data.background || data.backgroundColor || data.backgroundImage || data.backgroundVideo || data.backgroundIframe ) {
            element.setAttribute( 'data-background-hash', data.background +
            data.backgroundSize +
            data.backgroundImage +
            data.backgroundVideo +
            data.backgroundIframe +
            data.backgroundColor +
            data.backgroundRepeat +
            data.backgroundPosition +
            data.backgroundTransition );
        }

        // Additional and optional background properties
        if( data.backgroundSize ) element.style.backgroundSize = data.backgroundSize;
        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 );

        // If backgrounds are being recreated, clear old classes
        slide.classList.remove( 'has-dark-background' );
        slide.classList.remove( 'has-light-background' );

        // If this slide has a background color, add a class that
        // signals if it is light or dark. If the slide has no background
        // color, no class will be set
        var computedBackgroundColor = window.getComputedStyle( element ).backgroundColor;
        if( computedBackgroundColor ) {
            var rgb = colorToRgb( computedBackgroundColor );

            // Ignore fully transparent backgrounds. Some browsers return
            // rgba(0,0,0,0) when reading the computed background color of
            // an element with no background
            if( rgb && rgb.a !== 0 ) {
                if( colorBrightness( computedBackgroundColor ) < 128 ) {
                    slide.classList.add( 'has-dark-background' );
                }
                else {
                    slide.classList.add( 'has-light-background' );
                }
            }
        }

        return element;

    }

    /**
     * Registers a listener to postMessage events, this makes it
     * possible to call all reveal.js API methods from another
     * window. For example:
     *
     * revealWindow.postMessage( JSON.stringify({
	 *   method: 'slide',
	 *   args: [ 2 ]
	 * }), '*' );
     */
    function setupPostMessage() {

        if( config.postMessage ) {
            window.addEventListener( 'message', function ( event ) {
                var data = event.data;

                // Make sure we're dealing with JSON
                if( typeof data === 'string' && data.charAt( 0 ) === '{' && data.charAt( data.length - 1 ) === '}' ) {
                    data = JSON.parse( data );

                    // Check if the requested method can be found
                    if( data.method && typeof Reveal[data.method] === 'function' ) {
                        Reveal[data.method].apply( Reveal, data.args );
                    }
                }
            }, false );
        }

    }

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

        var numberOfSlides = dom.wrapper.querySelectorAll( SLIDES_SELECTOR ).length;

        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( features.transforms3d === 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 );

        dom.controls.style.display = config.controls ? 'block' : 'none';
        dom.progress.style.display = config.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' );
        }

        // Exit the paused mode if it was configured off
        if( config.pause === false ) {
            resume();
        }

        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]' );
        }

        // Remove existing auto-slide controls
        if( autoSlidePlayer ) {
            autoSlidePlayer.destroy();
            autoSlidePlayer = null;
        }

        // Generate auto-slide controls if needed
        if( numberOfSlides > 1 && config.autoSlide && config.autoSlideStoppable && features.canvas && features.requestAnimationFrame ) {
            autoSlidePlayer = new Playback( dom.wrapper, function() {
                return Math.min( Math.max( ( Date.now() - autoSlideStartTime ) / autoSlide, 0 ), 1 );
            } );

            autoSlidePlayer.on( 'click', onAutoSlidePlayerClick );
            autoSlidePaused = false;
        }

        // When fragments are turned off they should be visible
        if( config.fragments === false ) {
            toArray( dom.slides.querySelectorAll( '.fragment' ) ).forEach( function( element ) {
                element.classList.add( 'visible' );
                element.classList.remove( 'current-fragment' );
            } );
        }

        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.pointerEnabled ) {
                // IE 11 uses un-prefixed version of pointer events
                dom.wrapper.addEventListener( 'pointerdown', onPointerDown, false );
                dom.wrapper.addEventListener( 'pointermove', onPointerMove, false );
                dom.wrapper.addEventListener( 'pointerup', onPointerUp, false );
            }
            else if( window.navigator.msPointerEnabled ) {
                // IE 10 uses prefixed version of pointer events
                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 );
            document.addEventListener( 'keypress', onDocumentKeyPress, false );
        }

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

        if( config.focusBodyOnPageVisibilityChange ) {
            var visibilityChange;

            if( 'hidden' in document ) {
                visibilityChange = 'visibilitychange';
            }
            else if( 'msHidden' in document ) {
                visibilityChange = 'msvisibilitychange';
            }
            else if( 'webkitHidden' in document ) {
                visibilityChange = 'webkitvisibilitychange';
            }

            if( visibilityChange ) {
                document.addEventListener( visibilityChange, onPageVisibilityChange, false );
            }
        }

        // Listen to both touch and click events, in case the device
        // supports both
        var pointerEvents = [ 'touchstart', 'click' ];

        // Only support touch for Android, fixes double navigations in
        // stock browser
        if( navigator.userAgent.match( /android/gi ) ) {
            pointerEvents = [ 'touchstart' ];
        }

        pointerEvents.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 );
        document.removeEventListener( 'keypress', onDocumentKeyPress, 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 );

        // IE11
        if( window.navigator.pointerEnabled ) {
            dom.wrapper.removeEventListener( 'pointerdown', onPointerDown, false );
            dom.wrapper.removeEventListener( 'pointermove', onPointerMove, false );
            dom.wrapper.removeEventListener( 'pointerup', onPointerUp, false );
        }
        // IE10
        else 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 );
        }

        [ '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 );

    }

    /**
     * Utility for deserializing a value.
     */
    function deserialize( value ) {

        if( typeof value === 'string' ) {
            if( value === 'null' ) return null;
            else if( value === 'true' ) return true;
            else if( value === 'false' ) return false;
            else if( value.match( /^\d+$/ ) ) return parseFloat( value );
        }

        return value;

    }

    /**
     * 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.transform = transform;

    }

    /**
     * Applies CSS transforms to the slides container. The container
     * is transformed from two separate sources: layout and the overview
     * mode.
     */
    function transformSlides( transforms ) {

        // Pick up new transforms from arguments
        if( typeof transforms.layout === 'string' ) slidesTransform.layout = transforms.layout;
        if( typeof transforms.overview === 'string' ) slidesTransform.overview = transforms.overview;

        // Apply the transforms to the slides container
        if( slidesTransform.layout ) {
            transformElement( dom.slides, slidesTransform.layout + ' ' + slidesTransform.overview );
        }
        else {
            transformElement( dom.slides, slidesTransform.overview );
        }

    }

    /**
     * Injects the given CSS styles into the DOM.
     */
    function injectStyleSheet( value ) {

        var tag = document.createElement( 'style' );
        tag.type = 'text/css';
        if( tag.styleSheet ) {
            tag.styleSheet.cssText = value;
        }
        else {
            tag.appendChild( document.createTextNode( value ) );
        }
        document.getElementsByTagName( 'head' )[0].appendChild( tag );

    }

    /**
     * Measures the distance in pixels between point a and point b.
     *
     * @param {String} color The string representation of a color,
     * the following formats are supported:
     * - #000
     * - #000000
     * - rgb(0,0,0)
     */
    function colorToRgb( color ) {

        var hex3 = color.match( /^#([0-9a-f]{3})$/i );
        if( hex3 && hex3[1] ) {
            hex3 = hex3[1];
            return {
                r: parseInt( hex3.charAt( 0 ), 16 ) * 0x11,
                g: parseInt( hex3.charAt( 1 ), 16 ) * 0x11,
                b: parseInt( hex3.charAt( 2 ), 16 ) * 0x11
            };
        }

        var hex6 = color.match( /^#([0-9a-f]{6})$/i );
        if( hex6 && hex6[1] ) {
            hex6 = hex6[1];
            return {
                r: parseInt( hex6.substr( 0, 2 ), 16 ),
                g: parseInt( hex6.substr( 2, 2 ), 16 ),
                b: parseInt( hex6.substr( 4, 2 ), 16 )
            };
        }

        var rgb = color.match( /^rgb\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\)$/i );
        if( rgb ) {
            return {
                r: parseInt( rgb[1], 10 ),
                g: parseInt( rgb[2], 10 ),
                b: parseInt( rgb[3], 10 )
            };
        }

        var rgba = color.match( /^rgba\s*\(\s*(\d+)\s*,\s*(\d+)\s*,\s*(\d+)\s*\,\s*([\d]+|[\d]*.[\d]+)\s*\)$/i );
        if( rgba ) {
            return {
                r: parseInt( rgba[1], 10 ),
                g: parseInt( rgba[2], 10 ),
                b: parseInt( rgba[3], 10 ),
                a: parseFloat( rgba[4] )
            };
        }

        return null;

    }

    /**
     * Calculates brightness on a scale of 0-255.
     *
     * @param color See colorStringToRgb for supported formats.
     */
    function colorBrightness( color ) {

        if( typeof color === 'string' ) color = colorToRgb( color );

        if( color ) {
            return ( color.r * 299 + color.g * 587 + color.b * 114 ) / 1000;
        }

        return null;

    }

    /**
     * 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( window.getComputedStyle( child ).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.
     *
     * remaining height = [ configured parent height ] - [ current parent height ]
     */
    function getRemainingHeight( element, height ) {

        height = height || 0;

        if( element ) {
            var newHeight, oldHeight = element.style.height;

            // Change the .stretch element height to 0 in order find the height of all
            // the other elements
            element.style.height = '0px';
            newHeight = height - element.parentNode.offsetHeight;

            // Restore the old height, just in case
            element.style.height = oldHeight + 'px';

            return newHeight;
        }

        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( config.hideAddressBar && isMobileDevice ) {
            // 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() {

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

    }

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

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

        // If we're in an iframe, post each reveal.js event to the
        // parent window. Used by the notes plugin
        if( config.postMessageEvents && window.parent !== window.self ) {
            window.parent.postMessage( JSON.stringify({ namespace: 'reveal', eventName: type, state: getState() }), '*' );
        }

    }

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

        if( features.transforms3d && !( 'msPerspective' in document.body.style ) ) {
            var anchors = dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ' a' );

            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 = dom.wrapper.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 showPreview( url ) {

        closeOverlay();

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

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

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

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

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

    }

    /**
     * Opens a overlay window with help material.
     */
    function showHelp() {

        if( config.help ) {

            closeOverlay();

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

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

            html += '<table><th>KEY</th><th>ACTION</th>';
            for( var key in keyboardShortcuts ) {
                html += '<tr><td>' + key + '</td><td>' + keyboardShortcuts[ key ] + '</td></tr>';
            }

            html += '</table>';

            dom.overlay.innerHTML = [
                '<header>',
                '<a class="close" href="#"><span class="icon"></span></a>',
                '</header>',
                '<div class="viewport">',
                '<div class="viewport-inner">'+ html +'</div>',
                '</div>'
            ].join('');

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

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

        }

    }

    /**
     * Closes any currently open overlay.
     */
    function closeOverlay() {

        if( dom.overlay ) {
            dom.overlay.parentNode.removeChild( dom.overlay );
            dom.overlay = null;
        }

    }

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

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

            var size = getComputedSlideSize();

            var slidePadding = 20; // TODO Dig this out of DOM

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

            dom.slides.style.width = size.width + 'px';
            dom.slides.style.height = size.height + 'px';

            // Determine scale of content to fit within available space
            scale = Math.min( size.presentationWidth / size.width, size.presentationHeight / size.height );

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

            // Don't apply any scaling styles if scale is 1
            if( scale === 1 ) {
                dom.slides.style.zoom = '';
                dom.slides.style.left = '';
                dom.slides.style.top = '';
                dom.slides.style.bottom = '';
                dom.slides.style.right = '';
                transformSlides( { layout: '' } );
            }
            else {
                // Prefer zooming in desktop Chrome so that content remains crisp
                if( !isMobileDevice && /chrome/i.test( navigator.userAgent ) && typeof dom.slides.style.zoom !== 'undefined' ) {
                    dom.slides.style.zoom = scale;
                    dom.slides.style.marginTop = config.marginTop;
                    dom.slides.style.marginLeft = config.marginLeft;
                    transformSlides( { layout: '' } );
                }
                // Apply scale transform as a fallback
                else {
                    // dom.slides.style.left = '50%';
                    // dom.slides.style.top = '44%';
                    // dom.slides.style.bottom = 'auto';
                    // dom.slides.style.right = 'auto';
                    dom.slides.style.marginTop = config.marginTop;
                    dom.slides.style.marginLeft = config.marginLeft;
                    dom.slides.style.marginBottom = 'auto';
                    dom.slides.style.marginRight = 'auto';
                    transformSlides( { layout: 'translate(-50%, -50%) scale('+ scale +') translate(50%, 50%)' } );
                }
            }

            // Select all slides, vertical and horizontal
            var slides = toArray( dom.wrapper.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 || slide.classList.contains( '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( ( ( size.height - getAbsoluteHeight( slide ) ) / 2 ) - slidePadding, 0 ) + 'px';
                    }
                }
                else {
                    slide.style.top = '';
                }

            }

            updateProgress();
            updateParallax();

        }

    }

    /**
     * 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 );

            // 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';
            }

        } );

    }

    /**
     * Calculates the computed pixel size of our slides. These
     * values are based on the width and height configuration
     * options.
     */
    function getComputedSlideSize( presentationWidth, presentationHeight ) {

        var size = {
            // Slide size
            width: config.width,
            height: config.height,

            // Presentation size
            presentationWidth: presentationWidth || dom.wrapper.offsetWidth,
            presentationHeight: presentationHeight || dom.wrapper.offsetHeight
        };

        // Reduce available space by margin
        size.presentationWidth -= ( size.presentationHeight * config.margin );
        size.presentationHeight -= ( size.presentationHeight * config.margin );

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

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

        return size;

    }

    /**
     * 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.
     */
    function activateOverview() {

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

            overview = true;

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

            if( features.overviewTransitions ) {
                setTimeout( function() {
                    dom.wrapper.classList.add( 'overview-animated' );
                }, 1 );
            }

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

            // Move the backgrounds element into the slide container to
            // that the same scaling is applied
            dom.slides.appendChild( dom.background );

            // Clicking on an overview slide navigates to it
            toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {
                if( !slide.classList.contains( 'stack' ) ) {
                    slide.addEventListener( 'click', onOverviewSlideClicked, true );
                }
            } );

            updateSlidesVisibility();
            layoutOverview();
            updateOverview();

            layout();

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

        }

    }

    /**
     * Uses CSS transforms to position all slides in a grid for
     * display inside of the overview mode.
     */
    function layoutOverview() {

        var margin = 70;
        var slideWidth = config.width + margin,
            slideHeight = config.height + margin;

        // Reverse in RTL mode
        if( config.rtl ) {
            slideWidth = -slideWidth;
        }

        // Layout slides
        toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).forEach( function( hslide, h ) {
            hslide.setAttribute( 'data-index-h', h );
            transformElement( hslide, 'translate3d(' + ( h * slideWidth ) + 'px, 0, 0)' );

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

                toArray( hslide.querySelectorAll( 'section' ) ).forEach( function( vslide, v ) {
                    vslide.setAttribute( 'data-index-h', h );
                    vslide.setAttribute( 'data-index-v', v );

                    transformElement( vslide, 'translate3d(0, ' + ( v * slideHeight ) + 'px, 0)' );
                } );

            }
        } );

        // Layout slide backgrounds
        toArray( dom.background.childNodes ).forEach( function( hbackground, h ) {
            transformElement( hbackground, 'translate3d(' + ( h * slideWidth ) + 'px, 0, 0)' );

            toArray( hbackground.querySelectorAll( '.slide-background' ) ).forEach( function( vbackground, v ) {
                transformElement( vbackground, 'translate3d(0, ' + ( v * slideHeight ) + 'px, 0)' );
            } );
        } );

    }

    /**
     * Moves the overview viewport to the current slides.
     * Called each time the current slide changes.
     */
    function updateOverview() {

        var margin = 70;
        var slideWidth = config.width + margin,
            slideHeight = config.height + margin;

        // Reverse in RTL mode
        if( config.rtl ) {
            slideWidth = -slideWidth;
        }

        transformSlides( {
            overview: [
                'translateX('+ ( -indexh * slideWidth ) +'px)',
                'translateY('+ ( -indexv * slideHeight ) +'px)',
                'translateZ('+ ( window.innerWidth < 400 ? -1000 : -2500 ) +'px)'
            ].join( ' ' )
        } );

    }

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

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

            overview = false;

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

            // 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( 'overview-deactivating' );

            setTimeout( function () {
                dom.wrapper.classList.remove( 'overview-deactivating' );
            }, 1 );

            // Move the background element back out
            dom.wrapper.appendChild( dom.background );

            // Clean up changes made to slides
            toArray( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( function( slide ) {
                transformElement( slide, '' );

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

            // Clean up changes made to backgrounds
            toArray( dom.background.querySelectorAll( '.slide-background' ) ).forEach( function( background ) {
                transformElement( background, '' );
            } );

            transformSlides( { overview: '' } );

            slide( indexh, indexv );

            layout();

            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 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 && !!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() {

        if( config.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( override ) {

        if( typeof override === 'boolean' ) {
            override ? pause() : resume();
        }
        else {
            isPaused() ? resume() : pause();
        }

    }

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

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

    }

    /**
     * Toggles the auto slide mode on and off.
     *
     * @param {Boolean} override Optional flag which sets the desired state.
     * True means autoplay starts, false means it stops.
     */

    function toggleAutoSlide( override ) {

        if( typeof override === 'boolean' ) {
            override ? resumeAutoSlide() : pauseAutoSlide();
        }

        else {
            autoSlidePaused ? resumeAutoSlide() : pauseAutoSlide();
        }

    }

    /**
     * Checks if the auto slide mode is currently on.
     */
    function isAutoSliding() {

        return !!( autoSlide && !autoSlidePaused );

    }

    /**
     * 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 = dom.wrapper.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 && !isOverview() ) {
            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() );
        }

        // Update the overview if it's currently active
        if( isOverview() ) {
            updateOverview();
        }

        // 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' ) {
            navigateFragment( f );
        }

        // 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' );
            previousSlide.setAttribute( 'aria-hidden', 'true' );

            // Reset all slides upon navigate to home
            // Issue: #285
            if ( dom.wrapper.querySelector( HOME_SLIDE_SELECTOR ).classList.contains( 'present' ) ) {
                // Launch async task
                setTimeout( function () {
                    var slides = toArray( dom.wrapper.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 || !previousSlide ) {
            stopEmbeddedContent( previousSlide );
            startEmbeddedContent( currentSlide );
        }

        // Announce the current slide contents, for screen readers
        dom.statusDiv.textContent = currentSlide.textContent;

        updateControls();
        updateProgress();
        updateBackground();
        updateParallax();
        updateSlideNumber();

        // Update the URL hash
        writeURL();

        cueAutoSlide();

    }

    /**
     * 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();

        // Write the current hash to the URL
        writeURL();

        sortAllFragments();

        updateControls();
        updateProgress();
        updateBackground( true );
        updateSlideNumber();
        updateSlidesVisibility();

        formatEmbeddedContent();

        if( isOverview() ) {
            layoutOverview();
        }

    }

    /**
     * Resets all vertical slides so that only the first
     * is visible.
     */
    function resetVerticalSlides() {

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

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

                if( y > 0 ) {
                    verticalSlide.classList.remove( 'present' );
                    verticalSlide.classList.remove( 'past' );
                    verticalSlide.classList.add( 'future' );
                    verticalSlide.setAttribute( 'aria-hidden', 'true' );
                }

            } );

        } );

    }

    /**
     * Sorts and formats all of fragments in the
     * presentation.
     */
    function sortAllFragments() {

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

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

                sortFragments( verticalSlide.querySelectorAll( '.fragment' ) );

            } );

            if( verticalSlides.length === 0 ) sortFragments( horizontalSlide.querySelectorAll( '.fragment' ) );

        } );

    }

    /**
     * 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( dom.wrapper.querySelectorAll( selector ) ),
            slidesLength = slides.length;

        var printMode = isPrintingPDF();

        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', '' );
                element.setAttribute( 'aria-hidden', 'true' );

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

                // If we're printing static slides, all slides are "present"
                if( printMode ) {
                    element.classList.add( 'present' );
                    continue;
                }

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

                    if( config.fragments ) {
                        var pastFragments = toArray( element.querySelectorAll( '.fragment' ) );

                        // Show all fragments on prior slides
                        while( pastFragments.length ) {
                            var pastFragment = pastFragments.pop();
                            pastFragment.classList.add( 'visible' );
                            pastFragment.classList.remove( 'current-fragment' );
                        }
                    }
                }
                else if( i > index ) {
                    // Any element subsequent to index is given the 'future' class
                    element.classList.add( reverse ? 'past' : 'future' );

                    if( config.fragments ) {
                        var futureFragments = toArray( element.querySelectorAll( '.fragment.visible' ) );

                        // No fragments in future slides should be visible ahead of time
                        while( futureFragments.length ) {
                            var futureFragment = futureFragments.pop();
                            futureFragment.classList.remove( 'visible' );
                            futureFragment.classList.remove( 'current-fragment' );
                        }
                    }
                }
            }

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

        }
        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( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ),
            horizontalSlidesLength = horizontalSlides.length,
            distanceX,
            distanceY;

        if( horizontalSlidesLength && typeof indexh !== 'undefined' ) {

            // 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 : 2;
            }

            // All slides need to be visible when exporting to PDF
            if( isPrintingPDF() ) {
                viewDistance = Number.MAX_VALUE;
            }

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

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

                // Determine how far away this slide is from the present
                distanceX = Math.abs( ( indexh || 0 ) - x ) || 0;

                // If the presentation is looped, distance should measure
                // 1 between the first and last slides
                if( config.loop ) {
                    distanceX = Math.abs( ( ( indexh || 0 ) - x ) % ( horizontalSlidesLength - viewDistance ) ) || 0;
                }

                // Show the horizontal slide if it's within the view distance
                if( distanceX < viewDistance ) {
                    showSlide( horizontalSlide );
                }
                else {
                    hideSlide( horizontalSlide );
                }

                if( verticalSlidesLength ) {

                    var oy = getPreviousVerticalIndex( horizontalSlide );

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

                        distanceY = x === ( indexh || 0 ) ? Math.abs( ( indexv || 0 ) - y ) : Math.abs( y - oy );

                        if( distanceX + distanceY < viewDistance ) {
                            showSlide( verticalSlide );
                        }
                        else {
                            hideSlide( verticalSlide );
                        }
                    }

                }
            }

        }

    }

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

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

            dom.progressbar.style.width = getProgress() * dom.wrapper.offsetWidth + 'px';

        }

    }

    /**
     * Updates the slide number div to reflect the current slide.
     *
     * Slide number format can be defined as a string using the
     * following variables:
     *  h: current slide's horizontal index
     *  v: current slide's vertical index
     *  c: current slide index (flattened)
     *  t: total number of slides (flattened)
     */
    function updateSlideNumber() {

        // Update slide number if enabled
        if( config.slideNumber && dom.slideNumber) {

            // Default to only showing the current slide number
            var format = 'c';

            // Check if a custom slide number format is available
            if( typeof config.slideNumber === 'string' ) {
                format = config.slideNumber;
            }

            var totalSlides = getTotalSlides();

            dom.slideNumber.innerHTML = format.replace( /h/g, indexh )
                .replace( /v/g, indexv )
                .replace( /c/g, Math.round( getProgress() * totalSlides ) + 1 )
                .replace( /t/g, totalSlides + 1 );
        }

    }

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

        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.
     *
     * @param {Boolean} includeAll If true, the backgrounds of
     * all vertical slides (not just the present) will be updated.
     */
    function updateBackground( includeAll ) {

        var currentBackground = null;

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

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

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

            if( h < indexh ) {
                backgroundh.classList.add( horizontalPast );
            }
            else if ( h > indexh ) {
                backgroundh.classList.add( horizontalFuture );
            }
            else {
                backgroundh.classList.add( 'present' );

                // Store a reference to the current background element
                currentBackground = backgroundh;
            }

            if( includeAll || h === indexh ) {
                toArray( backgroundh.querySelectorAll( '.slide-background' ) ).forEach( function( backgroundv, v ) {

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

                    if( v < indexv ) {
                        backgroundv.classList.add( 'past' );
                    }
                    else if ( v > indexv ) {
                        backgroundv.classList.add( 'future' );
                    }
                    else {
                        backgroundv.classList.add( 'present' );

                        // Only if this is the present horizontal and vertical slide
                        if( h === indexh ) currentBackground = backgroundv;
                    }

                } );
            }

        } );

        // Stop any currently playing video background
        if( previousBackground ) {

            var previousVideo = previousBackground.querySelector( 'video' );
            if( previousVideo ) previousVideo.pause();

        }

        if( currentBackground ) {

            // Start video playback
            var currentVideo = currentBackground.querySelector( 'video' );
            if( currentVideo ) {
                currentVideo.currentTime = 0;
                currentVideo.play();
            }

            var backgroundImageURL = currentBackground.style.backgroundImage || '';

            // Restart GIFs (doesn't work in Firefox)
            if( /\.gif/i.test( backgroundImageURL ) ) {
                currentBackground.style.backgroundImage = '';
                window.getComputedStyle( currentBackground ).opacity;
                currentBackground.style.backgroundImage = backgroundImageURL;
            }

            // Don't transition between identical backgrounds. This
            // prevents unwanted flicker.
            var previousBackgroundHash = previousBackground ? previousBackground.getAttribute( 'data-background-hash' ) : null;
            var currentBackgroundHash = currentBackground.getAttribute( 'data-background-hash' );
            if( currentBackgroundHash && currentBackgroundHash === previousBackgroundHash && currentBackground !== previousBackground ) {
                dom.background.classList.add( 'no-transition' );
            }

            previousBackground = currentBackground;

        }

        // If there's a background brightness flag for this slide,
        // bubble it to the .reveal container
        if( currentSlide ) {
            [ 'has-light-background', 'has-dark-background' ].forEach( function( classToBubble ) {
                if( currentSlide.classList.contains( classToBubble ) ) {
                    dom.wrapper.classList.add( classToBubble );
                }
                else {
                    dom.wrapper.classList.remove( classToBubble );
                }
            } );
        }

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

    }

    /**
     * Updates the position of the parallax background based
     * on the current slide index.
     */
    function updateParallax() {

        if( config.parallaxBackgroundImage ) {

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

            var backgroundSize = dom.background.style.backgroundSize.split( ' ' ),
                backgroundWidth, backgroundHeight;

            if( backgroundSize.length === 1 ) {
                backgroundWidth = backgroundHeight = parseInt( backgroundSize[0], 10 );
            }
            else {
                backgroundWidth = parseInt( backgroundSize[0], 10 );
                backgroundHeight = parseInt( backgroundSize[1], 10 );
            }

            var slideWidth = dom.background.offsetWidth,
                horizontalSlideCount = horizontalSlides.length,
                horizontalOffsetMultiplier,
                horizontalOffset;

            if( typeof config.parallaxBackgroundHorizontal === 'number' ) {
                horizontalOffsetMultiplier = config.parallaxBackgroundHorizontal;
            }
            else {
                horizontalOffsetMultiplier = ( backgroundWidth - slideWidth ) / ( horizontalSlideCount-1 );
            }

            horizontalOffset = horizontalOffsetMultiplier * indexh * -1;

            var slideHeight = dom.background.offsetHeight,
                verticalSlideCount = verticalSlides.length,
                verticalOffsetMultiplier,
                verticalOffset;

            if( typeof config.parallaxBackgroundVertical === 'number' ) {
                verticalOffsetMultiplier = config.parallaxBackgroundVertical;
            }
            else {
                verticalOffsetMultiplier = ( backgroundHeight - slideHeight ) / ( verticalSlideCount-1 );
            }

            verticalOffset = verticalSlideCount > 0 ?  verticalOffsetMultiplier * indexv * 1 : 0;

            dom.background.style.backgroundPosition = horizontalOffset + 'px ' + -verticalOffset + 'px';

        }

    }

    /**
     * Called when the given slide is within the configured view
     * distance. Shows the slide element and loads any content
     * that is set to load lazily (data-src).
     */
    function showSlide( slide ) {

        // Show the slide element
        slide.style.display = 'block';

        // Media elements with data-src attributes
        toArray( slide.querySelectorAll( 'img[data-src], video[data-src], audio[data-src], iframe[data-src]' ) ).forEach( function( element ) {
            element.setAttribute( 'src', element.getAttribute( 'data-src' ) );
            element.removeAttribute( 'data-src' );
        } );

        // Media elements with <source> children
        toArray( slide.querySelectorAll( 'video, audio' ) ).forEach( function( media ) {
            var sources = 0;

            toArray( media.querySelectorAll( 'source[data-src]' ) ).forEach( function( source ) {
                source.setAttribute( 'src', source.getAttribute( 'data-src' ) );
                source.removeAttribute( 'data-src' );
                sources += 1;
            } );

            // If we rewrote sources for this video/audio element, we need
            // to manually tell it to load from its new origin
            if( sources > 0 ) {
                media.load();
            }
        } );


        // Show the corresponding background element
        var indices = getIndices( slide );
        var background = getSlideBackground( indices.h, indices.v );
        if( background ) {
            background.style.display = 'block';

            // If the background contains media, load it
            if( background.hasAttribute( 'data-loaded' ) === false ) {
                background.setAttribute( 'data-loaded', 'true' );

                var backgroundImage = slide.getAttribute( 'data-background-image' ),
                    backgroundVideo = slide.getAttribute( 'data-background-video' ),
                    backgroundVideoLoop = slide.hasAttribute( 'data-background-video-loop' ),
                    backgroundIframe = slide.getAttribute( 'data-background-iframe' );

                // Images
                if( backgroundImage ) {
                    background.style.backgroundImage = 'url('+ backgroundImage +')';
                }
                // Videos
                else if ( backgroundVideo && !isSpeakerNotes() ) {
                    var video = document.createElement( 'video' );

                    if( backgroundVideoLoop ) {
                        video.setAttribute( 'loop', '' );
                    }

                    // Support comma separated lists of video sources
                    backgroundVideo.split( ',' ).forEach( function( source ) {
                        video.innerHTML += '<source src="'+ source +'">';
                    } );

                    background.appendChild( video );
                }
                // Iframes
                else if( backgroundIframe ) {
                    var iframe = document.createElement( 'iframe' );
                    iframe.setAttribute( 'src', backgroundIframe );
                    iframe.style.width  = '100%';
                    iframe.style.height = '100%';
                    iframe.style.maxHeight = '100%';
                    iframe.style.maxWidth = '100%';

                    background.appendChild( iframe );
                }
            }
        }

    }

    /**
     * Called when the given slide is moved outside of the
     * configured view distance.
     */
    function hideSlide( slide ) {

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

        // Hide the corresponding background element
        var indices = getIndices( slide );
        var background = getSlideBackground( indices.h, indices.v );
        if( background ) {
            background.style.display = 'none';
        }

    }

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

        var horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ),
            verticalSlides = dom.wrapper.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 };
        }

    }

    /**
     * Enforces origin-specific format rules for embedded media.
     */
    function formatEmbeddedContent() {

        // YouTube frames must include "?enablejsapi=1"
        toArray( dom.slides.querySelectorAll( 'iframe[src*="youtube.com/embed/"]' ) ).forEach( function( el ) {
            var src = el.getAttribute( 'src' );
            if( !/enablejsapi\=1/gi.test( src ) ) {
                el.setAttribute( 'src', src + ( !/\?/.test( src ) ? '?' : '&' ) + 'enablejsapi=1' );
            }
        });

        // Vimeo frames must include "?api=1"
        toArray( dom.slides.querySelectorAll( 'iframe[src*="player.vimeo.com/"]' ) ).forEach( function( el ) {
            var src = el.getAttribute( 'src' );
            if( !/api\=1/gi.test( src ) ) {
                el.setAttribute( 'src', src + ( !/\?/.test( src ) ? '?' : '&' ) + 'api=1' );
            }
        });

    }

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

        if( slide && !isSpeakerNotes() ) {
            // Restart GIFs
            toArray( slide.querySelectorAll( 'img[src$=".gif"]' ) ).forEach( function( el ) {
                // Setting the same unchanged source like this was confirmed
                // to work in Chrome, FF & Safari
                el.setAttribute( 'src', el.getAttribute( 'src' ) );
            } );

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

            // iframe embeds
            toArray( slide.querySelectorAll( 'iframe' ) ).forEach( function( el ) {
                el.contentWindow.postMessage( 'slide:start', '*' );
            });

            // 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":""}', '*' );
                }
            });

            // Vimeo embeds
            toArray( slide.querySelectorAll( 'iframe[src*="player.vimeo.com/"]' ) ).forEach( function( el ) {
                if( el.hasAttribute( 'data-autoplay' ) ) {
                    el.contentWindow.postMessage( '{"method":"play"}', '*' );
                }
            });
        }

    }

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

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

            // iframe embeds
            toArray( slide.querySelectorAll( 'iframe' ) ).forEach( function( el ) {
                el.contentWindow.postMessage( 'slide:stop', '*' );
            });

            // 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":""}', '*' );
                }
            });

            // Vimeo embeds
            toArray( slide.querySelectorAll( 'iframe[src*="player.vimeo.com/"]' ) ).forEach( function( el ) {
                if( !el.hasAttribute( 'data-ignore' ) && typeof el.contentWindow.postMessage === 'function' ) {
                    el.contentWindow.postMessage( '{"method":"pause"}', '*' );
                }
            });
        }

    }

    /**
     * Returns a value ranging from 0-1 that represents
     * how far into the presentation we have navigated.
     */
    function getProgress() {

        var horizontalSlides = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

        // The number of past and total slides
        var totalCount = getTotalSlides();
        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++;
            }

        }

        if( currentSlide ) {

            var allFragments = currentSlide.querySelectorAll( '.fragment' );

            // If there are fragments in the current slide those should be
            // accounted for in the progress.
            if( allFragments.length > 0 ) {
                var visibleFragments = currentSlide.querySelectorAll( '.fragment.visible' );

                // This value represents how big a portion of the slide progress
                // that is made up by its fragments (0-1)
                var fragmentWeight = 0.9;

                // Add fragment progress to the past slide count
                pastCount += ( visibleFragments.length / allFragments.length ) * fragmentWeight;
            }

        }

        return pastCount / ( totalCount - 1 );

    }

    /**
     * Checks if this presentation is running inside of the
     * speaker notes window.
     */
    function isSpeakerNotes() {

        return !!window.location.search.match( /receiver/gi );

    }

    /**
     * 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 ) {
            var element;

            // Ensure the named link is a valid HTML ID attribute
            if( /^[a-zA-Z][\w:.-]*$/.test( name ) ) {
                // Find the slide with the specified ID
                element = document.getElementById( 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 if( currentSlide ) {
                var url = '/';

                // Attempt to create a named link based on the slide's ID
                var id = currentSlide.getAttribute( 'id' );
                if( id ) {
                    id = id.toLowerCase();
                    id = id.replace( /[^a-zA-Z0-9\-\_\:\.]/g, '' );
                }

                // If the current slide has an ID, use that as a named link
                if( typeof id === 'string' && id.length ) {
                    url = '/' + 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( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) );

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

            // Assume we're not vertical
            v = undefined;

            // 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 currentFragment = currentSlide.querySelector( '.current-fragment' );
                if( currentFragment && currentFragment.hasAttribute( 'data-fragment-index' ) ) {
                    f = parseInt( currentFragment.getAttribute( 'data-fragment-index' ), 10 );
                }
                else {
                    f = currentSlide.querySelectorAll( '.fragment.visible' ).length - 1;
                }
            }
        }

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

    }

    /**
     * Retrieves the total number of slides in this presentation.
     */
    function getTotalSlides() {

        return dom.wrapper.querySelectorAll( SLIDES_SELECTOR + ':not(.stack)' ).length;

    }

    /**
     * Returns the slide element matching the specified index.
     */
    function getSlide( x, y ) {

        var horizontalSlide = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR )[ x ];
        var verticalSlides = horizontalSlide && horizontalSlide.querySelectorAll( 'section' );

        if( verticalSlides && verticalSlides.length && typeof y === 'number' ) {
            return verticalSlides ? verticalSlides[ y ] : undefined;
        }

        return horizontalSlide;

    }

    /**
     * Returns the background element for the given slide.
     * All slides, even the ones with no background properties
     * defined, have a background element so as long as the
     * index is valid an element will be returned.
     */
    function getSlideBackground( x, y ) {

        // When printing to PDF the slide backgrounds are nested
        // inside of the slides
        if( isPrintingPDF() ) {
            var slide = getSlide( x, y );
            if( slide ) {
                var background = slide.querySelector( '.slide-background' );
                if( background && background.parentNode === slide ) {
                    return background;
                }
            }

            return undefined;
        }

        var horizontalBackground = dom.wrapper.querySelectorAll( '.backgrounds>.slide-background' )[ x ];
        var verticalBackgrounds = horizontalBackground && horizontalBackground.querySelectorAll( '.slide-background' );

        if( verticalBackgrounds && verticalBackgrounds.length && typeof y === 'number' ) {
            return verticalBackgrounds ? verticalBackgrounds[ y ] : undefined;
        }

        return horizontalBackground;

    }

    /**
     * Retrieves the current state of the presentation as
     * an object. This state can then be restored at any
     * time.
     */
    function getState() {

        var indices = getIndices();

        return {
            indexh: indices.h,
            indexv: indices.v,
            indexf: indices.f,
            paused: isPaused(),
            overview: isOverview()
        };

    }

    /**
     * Restores the presentation to the given state.
     *
     * @param {Object} state As generated by getState()
     */
    function setState( state ) {

        if( typeof state === 'object' ) {
            slide( deserialize( state.indexh ), deserialize( state.indexv ), deserialize( state.indexf ) );

            var pausedFlag = deserialize( state.paused ),
                overviewFlag = deserialize( state.overview );

            if( typeof pausedFlag === 'boolean' && pausedFlag !== isPaused() ) {
                togglePause( pausedFlag );
            }

            if( typeof overviewFlag === 'boolean' && overviewFlag !== isOverview() ) {
                toggleOverview( overviewFlag );
            }
        }

    }

    /**
     * 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 ) {

        fragments = toArray( fragments );

        var ordered = [],
            unordered = [],
            sorted = [];

        // Group ordered and unordered elements
        fragments.forEach( function( fragment, i ) {
            if( fragment.hasAttribute( 'data-fragment-index' ) ) {
                var index = parseInt( fragment.getAttribute( 'data-fragment-index' ), 10 );

                if( !ordered[index] ) {
                    ordered[index] = [];
                }

                ordered[index].push( fragment );
            }
            else {
                unordered.push( [ fragment ] );
            }
        } );

        // Append fragments without explicit indices in their
        // DOM order
        ordered = ordered.concat( unordered );

        // Manually count the index up per group to ensure there
        // are no gaps
        var index = 0;

        // Push all fragments in their sorted order to an array,
        // this flattens the groups
        ordered.forEach( function( group ) {
            group.forEach( function( fragment ) {
                sorted.push( fragment );
                fragment.setAttribute( 'data-fragment-index', index );
            } );

            index ++;
        } );

        return sorted;

    }

    /**
     * Navigate to the specified slide fragment.
     *
     * @param {Number} index The index of the fragment that
     * should be shown, -1 means all are invisible
     * @param {Number} offset Integer offset to apply to the
     * fragment index
     *
     * @return {Boolean} true if a change was made in any
     * fragments visibility as part of this call
     */
    function navigateFragment( index, offset ) {

        if( currentSlide && config.fragments ) {

            var fragments = sortFragments( currentSlide.querySelectorAll( '.fragment' ) );
            if( fragments.length ) {

                // If no index is specified, find the current
                if( typeof index !== 'number' ) {
                    var lastVisibleFragment = sortFragments( currentSlide.querySelectorAll( '.fragment.visible' ) ).pop();

                    if( lastVisibleFragment ) {
                        index = parseInt( lastVisibleFragment.getAttribute( 'data-fragment-index' ) || 0, 10 );
                    }
                    else {
                        index = -1;
                    }
                }

                // If an offset is specified, apply it to the index
                if( typeof offset === 'number' ) {
                    index += offset;
                }

                var fragmentsShown = [],
                    fragmentsHidden = [];

                toArray( fragments ).forEach( function( element, i ) {

                    if( element.hasAttribute( 'data-fragment-index' ) ) {
                        i = parseInt( element.getAttribute( 'data-fragment-index' ), 10 );
                    }

                    // Visible fragments
                    if( i <= index ) {
                        if( !element.classList.contains( 'visible' ) ) fragmentsShown.push( element );
                        element.classList.add( 'visible' );
                        element.classList.remove( 'current-fragment' );

                        // Announce the fragments one by one to the Screen Reader
                        dom.statusDiv.textContent = element.textContent;

                        if( i === index ) {
                            element.classList.add( 'current-fragment' );
                        }
                    }
                    // Hidden fragments
                    else {
                        if( element.classList.contains( 'visible' ) ) fragmentsHidden.push( element );
                        element.classList.remove( 'visible' );
                        element.classList.remove( 'current-fragment' );
                    }


                } );

                if( fragmentsHidden.length ) {
                    dispatchEvent( 'fragmenthidden', { fragment: fragmentsHidden[0], fragments: fragmentsHidden } );
                }

                if( fragmentsShown.length ) {
                    dispatchEvent( 'fragmentshown', { fragment: fragmentsShown[0], fragments: fragmentsShown } );
                }

                updateControls();
                updateProgress();

                return !!( fragmentsShown.length || fragmentsHidden.length );

            }

        }

        return false;

    }

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

        return navigateFragment( null, 1 );

    }

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

        return navigateFragment( null, -1 );

    }

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

        cancelAutoSlide();

        if( currentSlide ) {

            var currentFragment = currentSlide.querySelector( '.current-fragment' );

            var fragmentAutoSlide = currentFragment ? currentFragment.getAttribute( 'data-autoslide' ) : null;
            var parentAutoSlide = currentSlide.parentNode ? currentSlide.parentNode.getAttribute( 'data-autoslide' ) : null;
            var slideAutoSlide = currentSlide.getAttribute( 'data-autoslide' );

            // Pick value in the following priority order:
            // 1. Current fragment's data-autoslide
            // 2. Current slide's data-autoslide
            // 3. Parent slide's data-autoslide
            // 4. Global autoSlide setting
            if( fragmentAutoSlide ) {
                autoSlide = parseInt( fragmentAutoSlide, 10 );
            }
            else if( slideAutoSlide ) {
                autoSlide = parseInt( slideAutoSlide, 10 );
            }
            else if( parentAutoSlide ) {
                autoSlide = parseInt( parentAutoSlide, 10 );
            }
            else {
                autoSlide = config.autoSlide;
            }

            // If there are media elements with data-autoplay,
            // automatically set the autoSlide duration to the
            // length of that media
            toArray( currentSlide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
                if( el.hasAttribute( 'data-autoplay' ) ) {
                    if( autoSlide && el.duration * 1000 > autoSlide ) {
                        autoSlide = ( el.duration * 1000 ) + 1000;
                    }
                }
            } );

            // Cue the next auto-slide if:
            // - There is an autoSlide value
            // - Auto-sliding isn't paused by the user
            // - The presentation isn't paused
            // - The overview isn't active
            // - The presentation isn't over
            if( autoSlide && !autoSlidePaused && !isPaused() && !isOverview() && ( !Reveal.isLastSlide() || availableFragments().next || config.loop === true ) ) {
                autoSlideTimeout = setTimeout( navigateNext, autoSlide );
                autoSlideStartTime = Date.now();
            }

            if( autoSlidePlayer ) {
                autoSlidePlayer.setPlaying( autoSlideTimeout !== -1 );
            }

        }

    }

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

        clearTimeout( autoSlideTimeout );
        autoSlideTimeout = -1;

    }

    function pauseAutoSlide() {

        if( autoSlide && !autoSlidePaused ) {
            autoSlidePaused = true;
            dispatchEvent( 'autoslidepaused' );
            clearTimeout( autoSlideTimeout );

            if( autoSlidePlayer ) {
                autoSlidePlayer.setPlaying( false );
            }
        }

    }

    function resumeAutoSlide() {

        if( autoSlide && autoSlidePaused ) {
            autoSlidePaused = false;
            dispatchEvent( 'autoslideresumed' );
            cueAutoSlide();
        }

    }

    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;

                if( config.rtl ) {
                    previousSlide = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.future' ) ).pop();
                }
                else {
                    previousSlide = toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR + '.past' ) ).pop();
                }

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

    }

    /**
     * The reverse of #navigatePrev().
     */
    function navigateNext() {

        // Prioritize revealing fragments
        if( nextFragment() === false ) {
            if( availableRoutes().down ) {
                navigateDown();
            }
            else if( config.rtl ) {
                navigateLeft();
            }
            else {
                navigateRight();
            }
        }

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

    }


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

    /**
     * Called by all event handlers that are based on user
     * input.
     */
    function onUserInput( event ) {

        if( config.autoSlideStoppable ) {
            pauseAutoSlide();
        }

    }

    /**
     * Handler for the document level 'keypress' event.
     */
    function onDocumentKeyPress( event ) {

        // Check if the pressed key is question mark
        if( event.shiftKey && event.charCode === 63 ) {
            if( dom.overlay ) {
                closeOverlay();
            }
            else {
                showHelp( true );
            }
        }

    }

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

        // If there's a condition specified and it returns false,
        // ignore this event
        if( typeof config.keyboardCondition === 'function' && config.keyboardCondition() === false ) {
            return true;
        }

        // Remember if auto-sliding was paused so we can toggle it
        var autoSlideWasPaused = autoSlidePaused;

        onUserInput( event );

        // Check if there's a focused element that could be using
        // the keyboard
        var activeElementIsCE = document.activeElement && document.activeElement.contentEditable !== 'inherit';
        var activeElementIsInput = document.activeElement && document.activeElement.tagName && /input|textarea/i.test( document.activeElement.tagName );

        // Disregard the event if there's a focused element or a
        // keyboard modifier key is present
        if( activeElementIsCE || activeElementIsInput || (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;
                // two-spot, semicolon, b, period, Logitech presenter tools "black screen" button
                case 58: case 59: case 66: case 190: case 191: togglePause(); break;
                // f
                case 70: enterFullscreen(); break;
                // a
                case 65: if ( config.autoSlideStoppable ) toggleAutoSlide( autoSlideWasPaused ); break;
                default:
                    triggered = false;
            }

        }

        // If the input resulted in a triggered action we should prevent
        // the browsers default behavior
        if( triggered ) {
            event.preventDefault && event.preventDefault();
        }
        // ESC or O key
        else if ( ( event.keyCode === 27 || event.keyCode === 79 ) && features.transforms3d ) {
            if( dom.overlay ) {
                closeOverlay();
            }
            else {
                toggleOverview();
            }

            event.preventDefault && 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 ) {
            onUserInput( event );

            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.pointerType === "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.pointerType === "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.pointerType === "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 ) {

        onUserInput( event );

        event.preventDefault();

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

        if( config.rtl ) {
            slideIndex = slidesTotal - slideIndex;
        }

        slide( slideIndex );

    }

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

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

        readURL();

    }

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

        layout();

    }

    /**
     * Handle for the window level 'visibilitychange' event.
     */
    function onPageVisibilityChange( event ) {

        var isHidden =  document.webkitHidden ||
            document.msHidden ||
            document.hidden;

        // If, after clicking a link or similar and we're coming back,
        // focus the document.body to ensure we can use keyboard shortcuts
        if( isHidden === false && document.activeElement !== document.body ) {
            // Not all elements support .blur() - SVGs among them.
            if( typeof document.activeElement.blur === 'function' ) {
                document.activeElement.blur();
            }
            document.body.focus();
        }

    }

    /**
     * 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 ) {

        if( event.currentTarget && event.currentTarget.hasAttribute( 'href' ) ) {
            var url = event.currentTarget.getAttribute( 'href' );
            if( url ) {
                showPreview( url );
                event.preventDefault();
            }
        }

    }

    /**
     * Handles click on the auto-sliding controls element.
     */
    function onAutoSlidePlayerClick( event ) {

        // Replay
        if( Reveal.isLastSlide() && config.loop === false ) {
            slide( 0, 0 );
            resumeAutoSlide();
        }
        // Resume
        else if( autoSlidePaused ) {
            resumeAutoSlide();
        }
        // Pause
        else {
            pauseAutoSlide();
        }

    }


    // --------------------------------------------------------------------//
    // ------------------------ PLAYBACK COMPONENT ------------------------//
    // --------------------------------------------------------------------//


    /**
     * Constructor for the playback component, which displays
     * play/pause/progress controls.
     *
     * @param {HTMLElement} container The component will append
     * itself to this
     * @param {Function} progressCheck A method which will be
     * called frequently to get the current progress on a range
     * of 0-1
     */
    function Playback( container, progressCheck ) {

        // Cosmetics
        this.diameter = 50;
        this.thickness = 3;

        // Flags if we are currently playing
        this.playing = false;

        // Current progress on a 0-1 range
        this.progress = 0;

        // Used to loop the animation smoothly
        this.progressOffset = 1;

        this.container = container;
        this.progressCheck = progressCheck;

        this.canvas = document.createElement( 'canvas' );
        this.canvas.className = 'playback';
        this.canvas.width = this.diameter;
        this.canvas.height = this.diameter;
        this.context = this.canvas.getContext( '2d' );

        this.container.appendChild( this.canvas );

        this.render();

    }

    Playback.prototype.setPlaying = function( value ) {

        var wasPlaying = this.playing;

        this.playing = value;

        // Start repainting if we weren't already
        if( !wasPlaying && this.playing ) {
            this.animate();
        }
        else {
            this.render();
        }

    };

    Playback.prototype.animate = function() {

        var progressBefore = this.progress;

        this.progress = this.progressCheck();

        // When we loop, offset the progress so that it eases
        // smoothly rather than immediately resetting
        if( progressBefore > 0.8 && this.progress < 0.2 ) {
            this.progressOffset = this.progress;
        }

        this.render();

        if( this.playing ) {
            features.requestAnimationFrameMethod.call( window, this.animate.bind( this ) );
        }

    };

    /**
     * Renders the current progress and playback state.
     */
    Playback.prototype.render = function() {

        var progress = this.playing ? this.progress : 0,
            radius = ( this.diameter / 2 ) - this.thickness,
            x = this.diameter / 2,
            y = this.diameter / 2,
            iconSize = 14;

        // Ease towards 1
        this.progressOffset += ( 1 - this.progressOffset ) * 0.1;

        var endAngle = ( - Math.PI / 2 ) + ( progress * ( Math.PI * 2 ) );
        var startAngle = ( - Math.PI / 2 ) + ( this.progressOffset * ( Math.PI * 2 ) );

        this.context.save();
        this.context.clearRect( 0, 0, this.diameter, this.diameter );

        // Solid background color
        this.context.beginPath();
        this.context.arc( x, y, radius + 2, 0, Math.PI * 2, false );
        this.context.fillStyle = 'rgba( 0, 0, 0, 0.4 )';
        this.context.fill();

        // Draw progress track
        this.context.beginPath();
        this.context.arc( x, y, radius, 0, Math.PI * 2, false );
        this.context.lineWidth = this.thickness;
        this.context.strokeStyle = '#666';
        this.context.stroke();

        if( this.playing ) {
            // Draw progress on top of track
            this.context.beginPath();
            this.context.arc( x, y, radius, startAngle, endAngle, false );
            this.context.lineWidth = this.thickness;
            this.context.strokeStyle = '#fff';
            this.context.stroke();
        }

        this.context.translate( x - ( iconSize / 2 ), y - ( iconSize / 2 ) );

        // Draw play/pause icons
        if( this.playing ) {
            this.context.fillStyle = '#fff';
            this.context.fillRect( 0, 0, iconSize / 2 - 2, iconSize );
            this.context.fillRect( iconSize / 2 + 2, 0, iconSize / 2 - 2, iconSize );
        }
        else {
            this.context.beginPath();
            this.context.translate( 2, 0 );
            this.context.moveTo( 0, 0 );
            this.context.lineTo( iconSize - 2, iconSize / 2 );
            this.context.lineTo( 0, iconSize );
            this.context.fillStyle = '#fff';
            this.context.fill();
        }

        this.context.restore();

    };

    Playback.prototype.on = function( type, listener ) {
        this.canvas.addEventListener( type, listener, false );
    };

    Playback.prototype.off = function( type, listener ) {
        this.canvas.removeEventListener( type, listener, false );
    };

    Playback.prototype.destroy = function() {

        this.playing = false;

        if( this.canvas.parentNode ) {
            this.container.removeChild( this.canvas );
        }

    };


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


    Reveal = {
        initialize: initialize,
        configure: configure,
        sync: sync,

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

        // Fragment methods
        navigateFragment: navigateFragment,
        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,

        // Toggles the auto slide mode on/off
        toggleAutoSlide: toggleAutoSlide,

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

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

        // Facility for persisting and restoring the presentation state
        getState: getState,
        setState: setState,

        // Presentation progress on range of 0-1
        getProgress: getProgress,

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

        getTotalSlides: getTotalSlides,

        // Returns the slide element at the specified index
        getSlide: getSlide,

        // Returns the slide background element at the specified index
        getSlideBackground: getSlideBackground,

        // 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();
            } );

            // Basic deserialization
            for( var i in query ) {
                var value = query[ i ];

                query[ i ] = deserialize( unescape( value ) );
            }

            return query;
        },

        // Returns true if we're currently on the first slide
        isFirstSlide: function() {
            return ( indexh === 0 && indexv === 0 );
        },

        // Returns true if we're currently on the last slide
        isLastSlide: function() {
            if( currentSlide ) {
                // Does this slide has next a sibling?
                if( currentSlide.nextElementSibling ) return false;

                // If it's vertical, does its parent have a next sibling?
                if( isVerticalSlide( currentSlide ) && currentSlide.parentNode.nextElementSibling ) return false;

                return true;
            }

            return 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 );
            }
        },

        // Programatically triggers a keyboard event
        triggerKey: function( keyCode ) {
            onDocumentKeyDown( { keyCode: keyCode } );
        }
    };

    return Reveal;

}));