/*!

* reveal.js
* http://lab.hakim.se/reveal-js
* MIT licensed
*
* Copyright (C) 2016 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;

    // The reveal.js version
    var VERSION = '3.4.1';

    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',
            UA = navigator.userAgent,

            // Configuration 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: 0.04,

                    // Bounds for smallest/largest possible scale to apply to content
                    minScale: 0.2,
                    maxScale: 2.0,

                    // 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,

                    // Randomizes the order of slides each time the presentation loads
                    shuffle: 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 question-mark
                    // key is pressed
                    help: true,

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

                    // Flags if speaker notes should be visible to all viewers
                    showNotes: false,

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

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

                    // Use this method for navigation when auto-sliding (defaults to navigateNext)
                    autoSlideMethod: null,

                    // 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 visibility 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,

                    // The maximum number of pages a single slide can expand onto when printing
                    // to PDF, unlimited by default
                    pdfMaxPagesPerSlide: Number.POSITIVE_INFINITY,

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

                    // Script dependencies to load
                    dependencies: []

            },

            // Flags if Reveal.initialize() has been called
            initialized = false,

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

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

            // Holds the dimensions of our overview slides, including margins
            overviewSlideWidth = null,
            overviewSlideHeight = null,

            // 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,

            // Client is a desktop Chrome, see #checkCapabilities()
            isChrome,

            // 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 ) {

            // Make sure we only initialize once
            if( initialized === true ) return;

            initialized = true;

            checkCapabilities();

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

                    // Since JS won't be running any further, we load all lazy
                    // loading elements upfront
                    var images = toArray( document.getElementsByTagName( 'img' ) ),
                            iframes = toArray( document.getElementsByTagName( 'iframe' ) );

                    var lazyLoadable = images.concat( iframes );

                    for( var i = 0, len = lazyLoadable.length; i < len; i++ ) {
                            var element = lazyLoadable[i];
                            if( element.getAttribute( 'data-src' ) ) {
                                    element.setAttribute( 'src', element.getAttribute( 'data-src' ) );
                                    element.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() {

            isMobileDevice = /(iphone|ipod|ipad|android)/gi.test( UA );
            isChrome = /chrome/i.test( UA ) && !/edge/i.test( UA );

            var testElement = document.createElement( 'div' );

            features.transforms3d = 'WebkitPerspective' in testElement.style ||
                                                            'MozPerspective' in testElement.style ||
                                                            'msPerspective' in testElement.style ||
                                                            'OPerspective' in testElement.style ||
                                                            'perspective' in testElement.style;

            features.transforms2d = 'WebkitTransform' in testElement.style ||
                                                            'MozTransform' in testElement.style ||
                                                            'msTransform' in testElement.style ||
                                                            'OTransform' in testElement.style ||
                                                            'transform' in testElement.style;

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

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

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

            // Flags if we should use zoom instead of transform to scale
            // up slides. Zoom produces crisper results but has a lot of
            // xbrowser quirks so we only use it in whitelsited browsers.
            features.zoom = 'zoom' in testElement.style && !isMobileDevice &&
                                            ( isChrome || /Version\/[\d\.]+.*Safari/.test( UA ) );

    }

/**
 * 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 the slides from being scrolled out of view
            setupScrollPrevention();

            // 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;

                    dom.wrapper.classList.add( 'ready' );

                    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',
                    '<button class="navigate-left" aria-label="previous slide"></button>' +
                    '<button class="navigate-right" aria-label="next slide"></button>' +
                    '<button class="navigate-up" aria-label="above slide"></button>' +
                    '<button class="navigate-down" aria-label="below slide"></button>' );

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

            // Element containing notes that are visible to the audience
            dom.speakerNotes = createSingletonNode( dom.wrapper, 'div', 'speaker-notes', null );
            dom.speakerNotes.setAttribute( 'data-prevent-swipe', '' );
            dom.speakerNotes.setAttribute( 'tabindex', '0' );

            // 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.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.
     *
     * @return {HTMLElement}
     */
    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;

    }

    /**
     * Converts the given HTML element into a string of text
     * that can be announced to a screen reader. Hidden
     * elements are excluded.
     */
    function getStatusText( node ) {

            var text = '';

            // Text node
            if( node.nodeType === 3 ) {
                    text += node.textContent;
            }
            // Element node
            else if( node.nodeType === 1 ) {

                    var isAriaHidden = node.getAttribute( 'aria-hidden' );
                    var isDisplayHidden = window.getComputedStyle( node )['display'] === 'none';
                    if( isAriaHidden !== 'true' && !isDisplayHidden ) {

                            toArray( node.childNodes ).forEach( function( child ) {
                                    text += getStatusText( child );
                            } );

                    }

            }

            return text;

    }

    /**
     * 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 0 -1px 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';

            // Add each slide's index as attributes on itself, we need these
            // indices to generate slide numbers below
            toArray( dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR ) ).forEach( function( hslide, h ) {
                    hslide.setAttribute( 'data-index-h', h );

                    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 );
                            } );
                    }
            } );

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

                            // Adhere to configured pages per slide limit
                            numberOfPages = Math.min( numberOfPages, config.pdfMaxPagesPerSlide );

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

                            // Wrap the slide in a page element and hide its overflow
                            // so that no page ever flows onto another
                            var page = document.createElement( 'div' );
                            page.className = 'pdf-page';
                            page.style.height = ( pageHeight * numberOfPages ) + 'px';
                            slide.parentNode.insertBefore( page, slide );
                            page.appendChild( slide );

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

                            if( slide.slideBackgroundElement ) {
                                    page.insertBefore( slide.slideBackgroundElement, slide );
                            }

                            // Inject notes if `showNotes` is enabled
                            if( config.showNotes ) {

                                    // Are there notes for this slide?
                                    var notes = getSlideNotes( slide );
                                    if( notes ) {

                                            var notesSpacing = 8;
                                            var notesLayout = typeof config.showNotes === 'string' ? config.showNotes : 'inline';
                                            var notesElement = document.createElement( 'div' );
                                            notesElement.classList.add( 'speaker-notes' );
                                            notesElement.classList.add( 'speaker-notes-pdf' );
                                            notesElement.setAttribute( 'data-layout', notesLayout );
                                            notesElement.innerHTML = notes;

                                            if( notesLayout === 'separate-page' ) {
                                                    page.parentNode.insertBefore( notesElement, page.nextSibling );
                                            }
                                            else {
                                                    notesElement.style.left = notesSpacing + 'px';
                                                    notesElement.style.bottom = notesSpacing + 'px';
                                                    notesElement.style.width = ( pageWidth - notesSpacing*2 ) + 'px';
                                                    page.appendChild( notesElement );
                                            }

                                    }

                            }

                            // Inject slide numbers if `slideNumbers` are enabled
                            if( config.slideNumber ) {
                                    var slideNumberH = parseInt( slide.getAttribute( 'data-index-h' ), 10 ) + 1,
                                            slideNumberV = parseInt( slide.getAttribute( 'data-index-v' ), 10 ) + 1;

                                    var numberElement = document.createElement( 'div' );
                                    numberElement.classList.add( 'slide-number' );
                                    numberElement.classList.add( 'slide-number-pdf' );
                                    numberElement.innerHTML = formatSlideNumber( slideNumberH, '.', slideNumberV );
                                    page.appendChild( numberElement );
                            }
                    }

            } );

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

            // Notify subscribers that the PDF layout is good to go
            dispatchEvent( 'pdf-ready' );

    }

    /**
     * This is an unfortunate necessity. Some actions – such as
     * an input field being focused in an iframe or using the
     * keyboard to expand text selection beyond the bounds of
     * a slide – can trigger our content to be pushed out of view.
     * This scrolling can not be prevented by hiding overflow in
     * CSS (we already do) so we have to resort to repeatedly
     * checking if the slides have been offset :(
     */
    function setupScrollPrevention() {

            setInterval( function() {
                    if( dom.wrapper.scrollTop !== 0 || dom.wrapper.scrollLeft !== 0 ) {
                            dom.wrapper.scrollTop = 0;
                            dom.wrapper.scrollLeft = 0;
                    }
            }, 1000 );

    }

    /**
     * Creates an HTML element and returns a reference to it.
     * If the element already exists the existing instance will
     * be returned.
     *
     * @param {HTMLElement} container
     * @param {string} tagname
     * @param {string} classname
     * @param {string} innerHTML
     *
     * @return {HTMLElement}
     */
    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 = createBackground( slideh, dom.background );

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

                            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
     * @return {HTMLElement} New background div
     */
    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' );

            slide.slideBackgroundElement = element;

            // 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 computedBackgroundStyle = window.getComputedStyle( element );
            if( computedBackgroundStyle && computedBackgroundStyle.backgroundColor ) {
                    var rgb = colorToRgb( computedBackgroundStyle.backgroundColor );

                    // 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( computedBackgroundStyle.backgroundColor ) < 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.
     *
     * @param {object} options
     */
    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';
            dom.slideNumber.style.display = config.slideNumber && !isPrintingPDF() ? 'block' : 'none';

            if( config.shuffle ) {
                    shuffle();
            }

            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.showNotes ) {
                    dom.speakerNotes.classList.add( 'visible' );
                    dom.speakerNotes.setAttribute( 'data-layout', typeof config.showNotes === 'string' ? config.showNotes : 'inline' );
            }
            else {
                    dom.speakerNotes.classList.remove( 'visible' );
            }

            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( UA.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.
     *
     * @param {object} a
     * @param {object} b
     */
    function extend( a, b ) {

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

    }

    /**
     * Converts the target object to an array.
     *
     * @param {object} o
     * @return {object[]}
     */
    function toArray( o ) {

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

    }

    /**
     * Utility for deserializing a value.
     *
     * @param {*} value
     * @return {*}
     */
    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
     *
     * @return {number}
     */
    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.
     *
     * @param {HTMLElement} element
     * @param {string} transform
     */
    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.
     *
     * @param {object} transforms
     */
    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.
     *
     * @param {string} value
     */
    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 );

    }

    /**
     * Find the closest parent that matches the given
     * selector.
     *
     * @param {HTMLElement} target The child element
     * @param {String} selector The CSS selector to match
     * the parents against
     *
     * @return {HTMLElement} The matched parent or null
     * if no matching parent was found
     */
    function closestParent( target, selector ) {

            var parent = target.parentNode;

            while( parent ) {

                    // There's some overhead doing this each time, we don't
                    // want to rewrite the element prototype but should still
                    // be enough to feature detect once at startup...
                    var matchesMethod = parent.matches || parent.matchesSelector || parent.msMatchesSelector;

                    // If we find a match, we're all set
                    if( matchesMethod && matchesMethod.call( parent, selector ) ) {
                            return parent;
                    }

                    // Keep searching
                    parent = parent.parentNode;

            }

            return null;

    }

    /**
     * Converts various color input formats to an {r:0,g:0,b:0} object.
     *
     * @param {string} color The string representation of a color
     * @example
     * colorToRgb('#000');
     * @example
     * colorToRgb('#000000');
     * @example
     * colorToRgb('rgb(0,0,0)');
     * @example
     * colorToRgb('rgba(0,0,0)');
     *
     * @return {{r: number, g: number, b: number, [a]: number}|null}
     */
    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 {string} color See colorToRgb for supported formats.
     * @see {@link colorToRgb}
     */
    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;

    }

    /**
     * Returns the remaining height within the parent of the
     * target element.
     *
     * remaining height = [ configured parent height ] - [ current parent height ]
     * 
     * @param {HTMLElement} element
     * @param {number} [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.
     *
     * @param {string} [selector=a] - selector for anchors
     */
    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.
     *
     * @param {string} url - url for preview iframe src
     */
    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>',
                            '<small class="viewport-inner">',
                                    '<span class="x-frame-error">Unable to load iframe. This is likely due to the site\'s policy (x-frame-options).</span>',
                            '</small>',
                    '</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 an 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();

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

                    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 zoom for scaling up so that content remains crisp.
                            // Don't use zoom to scale down since that can lead to shifts
                            // in text layout/line breaks.
                            if( scale > 1 && features.zoom ) {
                                    dom.slides.style.zoom = scale;
                                    dom.slides.style.left = '';
                                    dom.slides.style.top = '';
                                    dom.slides.style.bottom = '';
                                    dom.slides.style.right = '';
                                    transformSlides( { layout: '' } );
                            }
                            // Apply scale transform as a fallback
                            else {
                                    dom.slides.style.zoom = '';
                                    dom.slides.style.left = '50%';
                                    dom.slides.style.top = '50%';
                                    dom.slides.style.bottom = 'auto';
                                    dom.slides.style.right = 'auto';
                                    transformSlides( { layout: 'translate(-50%, -50%) scale('+ scale +')' } );
                            }
                    }

                    // 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 - slide.scrollHeight ) / 2, 0 ) + 'px';
                                    }
                            }
                            else {
                                    slide.style.top = '';
                            }

                    }

                    updateProgress();
                    updateParallax();

            }

    }

    /**
     * Applies layout logic to the contents of all slides in
     * the presentation.
     *
     * @param {string|number} width
     * @param {string|number} height
     */
    function layoutSlideContents( width, height ) {

            // 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.
     *
     * @param {number} [presentationWidth=dom.wrapper.offsetWidth]
     * @param {number} [presentationHeight=dom.wrapper.offsetHeight]
     */
    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.presentationWidth * 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 {string|number} [v=0] 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 );
                            }
                    } );

                    // Calculate slide sizes
                    var margin = 70;
                    var slideSize = getComputedSlideSize();
                    overviewSlideWidth = slideSize.width + margin;
                    overviewSlideHeight = slideSize.height + margin;

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

                    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() {

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

                    }
            } );

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

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

    }

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

            transformSlides( {
                    overview: [
                            'translateX('+ ( -indexh * overviewSlideWidth ) +'px)',
                            'translateY('+ ( -indexv * overviewSlideHeight ) +'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] 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=currentSlide] The slide to check
     * orientation of
     * @return {Boolean}
     */
    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.documentElement;

            // 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.
     *
     * @return {Boolean}
     */
    function isPaused() {

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

    }

    /**
     * Toggles the auto slide mode on and off.
     *
     * @param {Boolean} [override] 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.
     *
     * @return {Boolean}
     */
    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 {number} [h=indexh] Horizontal index of the target slide
     * @param {number} [v=indexv] Vertical index of the target slide
     * @param {number} [f] Index of a fragment within the
     * target slide to activate
     * @param {number} [o] 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 );

            // Abort if there are no slides
            if( horizontalSlides.length === 0 ) return;

            // 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 = getStatusText( currentSlide );

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

            // 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();
            updateNotes();

            formatEmbeddedContent();
            startEmbeddedContent( currentSlide );

            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' ) );

            } );

    }

    /**
     * Randomly shuffles all slides in the deck.
     */
    function shuffle() {

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

            slides.forEach( function( slide ) {

                    // Insert this slide next to another random slide. This may
                    // cause the slide to insert before itself but that's fine.
                    dom.slides.insertBefore( slide, slides[ Math.floor( Math.random() * slides.length ) ] );

            } );

    }

    /**
     * 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 );
                                            }
                                    }

                            }
                    }

            }

    }

    /**
     * Pick up notes from the current slide and display them
     * to the viewer.
     *
     * @see {@link config.showNotes}
     */
    function updateNotes() {

            if( config.showNotes && dom.speakerNotes && currentSlide && !isPrintingPDF() ) {

                    dom.speakerNotes.innerHTML = getSlideNotes() || '';

            }

    }

    /**
     * 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.
     *
     * The following slide number formats are available:
     *  "h.v":      horizontal . vertical slide number (default)
     *  "h/v":      horizontal / vertical slide number
     *    "c":      flattened slide number
     *  "c/t":      flattened slide number / total slides
     */
    function updateSlideNumber() {

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

                    var value = [];
                    var format = 'h.v';

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

                    switch( format ) {
                            case 'c':
                                    value.push( getSlidePastCount() + 1 );
                                    break;
                            case 'c/t':
                                    value.push( getSlidePastCount() + 1, '/', getTotalSlides() );
                                    break;
                            case 'h/v':
                                    value.push( indexh + 1 );
                                    if( isVerticalSlide() ) value.push( '/', indexv + 1 );
                                    break;
                            default:
                                    value.push( indexh + 1 );
                                    if( isVerticalSlide() ) value.push( '.', indexv + 1 );
                    }

                    dom.slideNumber.innerHTML = formatSlideNumber( value[0], value[1], value[2] );
            }

    }

    /**
     * Applies HTML formatting to a slide number before it's
     * written to the DOM.
     *
     * @param {number} a Current slide
     * @param {string} delimiter Character to separate slide numbers
     * @param {(number|*)} b Total slides
     * @return {string} HTML string fragment
     */
    function formatSlideNumber( a, delimiter, b ) {

            if( typeof b === 'number' && !isNaN( b ) ) {
                    return  '<span class="slide-number-a">'+ a +'</span>' +
                                    '<span class="slide-number-delimiter">'+ delimiter +'</span>' +
                                    '<span class="slide-number-b">'+ b +'</span>';
            }
            else {
                    return '<span class="slide-number-a">'+ a +'</span>';
            }

    }

    /**
     * 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' );

                    // Set 'disabled' attribute on all directions
                    node.setAttribute( 'disabled', 'disabled' );
            } );

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

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

            // 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' ); el.removeAttribute( 'disabled' ); } );
                    if( fragments.next ) dom.controlsNext.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );

                    // 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' ); el.removeAttribute( 'disabled' ); } );
                            if( fragments.next ) dom.controlsDown.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );
                    }
                    else {
                            if( fragments.prev ) dom.controlsLeft.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );
                            if( fragments.next ) dom.controlsRight.forEach( function( el ) { el.classList.add( 'fragmented', 'enabled' ); el.removeAttribute( 'disabled' ); } );
                    }

            }

    }

    /**
     * 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 ) {

                            var startVideo = function() {
                                    currentVideo.currentTime = 0;
                                    currentVideo.play();
                                    currentVideo.removeEventListener( 'loadeddata', startVideo );
                            };

                            if( currentVideo.readyState > 1 ) {
                                    startVideo();
                            }
                            else {
                                    currentVideo.addEventListener( 'loadeddata', startVideo );
                            }

                    }

                    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 = horizontalSlideCount > 1 ? ( backgroundWidth - slideWidth ) / ( horizontalSlideCount-1 ) : 0;
                    }

                    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 : 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).
     *
     * @param {HTMLElement} slide Slide to show
     */
    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]' ) ).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' ),
                                    backgroundVideoMuted = slide.hasAttribute( 'data-background-video-muted' ),
                                    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', '' );
                                    }

                                    if( backgroundVideoMuted ) {
                                            video.muted = true;
                                    }

                                    // 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.
     *
     * @param {HTMLElement} slide
     */
    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 {{left: boolean, right: boolean, up: boolean, down: boolean}}
     */
    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 {{prev: boolean, next: boolean}}
     */
    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() {

            var _appendParamToIframeSource = function( sourceAttribute, sourceURL, param ) {
                    toArray( dom.slides.querySelectorAll( 'iframe['+ sourceAttribute +'*="'+ sourceURL +'"]' ) ).forEach( function( el ) {
                            var src = el.getAttribute( sourceAttribute );
                            if( src && src.indexOf( param ) === -1 ) {
                                    el.setAttribute( sourceAttribute, src + ( !/\?/.test( src ) ? '?' : '&' ) + param );
                            }
                    });
            };

            // YouTube frames must include "?enablejsapi=1"
            _appendParamToIframeSource( 'src', 'youtube.com/embed/', 'enablejsapi=1' );
            _appendParamToIframeSource( 'data-src', 'youtube.com/embed/', 'enablejsapi=1' );

            // Vimeo frames must include "?api=1"
            _appendParamToIframeSource( 'src', 'player.vimeo.com/', 'api=1' );
            _appendParamToIframeSource( 'data-src', 'player.vimeo.com/', 'api=1' );

    }

    /**
     * Start playback of any embedded content inside of
     * the given element.
     *
     * @param {HTMLElement} slide
     */
    function startEmbeddedContent( element ) {

            if( element && !isSpeakerNotes() ) {
                    // Restart GIFs
                    toArray( element.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( element.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
                            if( closestParent( el, '.fragment' ) && !closestParent( el, '.fragment.visible' ) ) {
                                    return;
                            }

                            if( el.hasAttribute( 'data-autoplay' ) && typeof el.play === 'function' ) {
                                    el.play();
                            }
                    } );

                    // Normal iframes
                    toArray( element.querySelectorAll( 'iframe[src]' ) ).forEach( function( el ) {
                            if( closestParent( el, '.fragment' ) && !closestParent( el, '.fragment.visible' ) ) {
                                    return;
                            }

                            startEmbeddedIframe( { target: el } );
                    } );

                    // Lazy loading iframes
                    toArray( element.querySelectorAll( 'iframe[data-src]' ) ).forEach( function( el ) {
                            if( closestParent( el, '.fragment' ) && !closestParent( el, '.fragment.visible' ) ) {
                                    return;
                            }

                            if( el.getAttribute( 'src' ) !== el.getAttribute( 'data-src' ) ) {
                                    el.removeEventListener( 'load', startEmbeddedIframe ); // remove first to avoid dupes
                                    el.addEventListener( 'load', startEmbeddedIframe );
                                    el.setAttribute( 'src', el.getAttribute( 'data-src' ) );
                            }
                    } );
            }

    }

    /**
     * "Starts" the content of an embedded iframe using the
     * postMessage API.
     *
     * @param {object} event - postMessage API event
     */
    function startEmbeddedIframe( event ) {

            var iframe = event.target;

            if( iframe && iframe.contentWindow ) {

                    // YouTube postMessage API
                    if( /youtube\.com\/embed\//.test( iframe.getAttribute( 'src' ) ) && iframe.hasAttribute( 'data-autoplay' ) ) {
                            iframe.contentWindow.postMessage( '{"event":"command","func":"playVideo","args":""}', '*' );
                    }
                    // Vimeo postMessage API
                    else if( /player\.vimeo\.com\//.test( iframe.getAttribute( 'src' ) ) && iframe.hasAttribute( 'data-autoplay' ) ) {
                            iframe.contentWindow.postMessage( '{"method":"play"}', '*' );
                    }
                    // Generic postMessage API
                    else {
                            iframe.contentWindow.postMessage( 'slide:start', '*' );
                    }

            }

    }

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

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

                    // Generic postMessage API for non-lazy loaded iframes
                    toArray( slide.querySelectorAll( 'iframe' ) ).forEach( function( el ) {
                            el.contentWindow.postMessage( 'slide:stop', '*' );
                            el.removeEventListener( 'load', startEmbeddedIframe );
                    });

                    // YouTube postMessage API
                    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 postMessage API
                    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"}', '*' );
                            }
                    });

                    // Lazy loading iframes
                    toArray( slide.querySelectorAll( 'iframe[data-src]' ) ).forEach( function( el ) {
                            // Only removing the src doesn't actually unload the frame
                            // in all browsers (Firefox) so we set it to blank first
                            el.setAttribute( 'src', 'about:blank' );
                            el.removeAttribute( 'src' );
                    } );
            }

    }

    /**
     * Returns the number of past slides. This can be used as a global
     * flattened index for slides.
     *
     * @return {number} Past slide count
     */
    function getSlidePastCount() {

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

            // The number of past slides
            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++;
                    }

            }

            return pastCount;

    }

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

            // The number of past and total slides
            var totalCount = getTotalSlides();
            var pastCount = getSlidePastCount();

            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.
     *
     * @return {boolean}
     */
    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.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 and fragment 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 {{h: number, v: number, f: number}}
     */
    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.
     *
     * @return {number}
     */
    function getTotalSlides() {

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

    }

    /**
     * Returns the slide element matching the specified index.
     *
     * @return {HTMLElement}
     */
    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.
     *
     * @param {number} x Horizontal background index
     * @param {number} y Vertical background index
     * @return {(HTMLElement[]|*)}
     */
    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 ) {
                            return slide.slideBackgroundElement;
                    }

                    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 speaker notes from a slide. Notes can be
     * defined in two ways:
     * 1. As a data-notes attribute on the slide <section>
     * 2. As an <aside class="notes"> inside of the slide
     *
     * @param {HTMLElement} [slide=currentSlide]
     * @return {(string|null)}
     */
    function getSlideNotes( slide ) {

            // Default to the current slide
            slide = slide || currentSlide;

            // Notes can be specified via the data-notes attribute...
            if( slide.hasAttribute( 'data-notes' ) ) {
                    return slide.getAttribute( 'data-notes' );
            }

            // ... or using an <aside class="notes"> element
            var notesElement = slide.querySelector( 'aside.notes' );
            if( notesElement ) {
                    return notesElement.innerHTML;
            }

            return null;

    }

    /**
     * Retrieves the current state of the presentation as
     * an object. This state can then be restored at any
     * time.
     *
     * @return {{indexh: number, indexv: number, indexf: number, paused: boolean, overview: boolean}}
     */
    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()
     * @see {@link getState} generates the parameter `state`
     */
    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.
     *
     * @param {object[]|*} fragments
     * @return {object[]} sorted Sorted array of fragments
     */
    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 = getStatusText( element );

                                            if( i === index ) {
                                                    element.classList.add( 'current-fragment' );
                                                    startEmbeddedContent( element );
                                            }
                                    }
                                    // 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 fragment = currentSlide.querySelector( '.current-fragment' );

                    // When the slide first appears there is no "current" fragment so
                    // we look for a data-autoslide timing on the first fragment
                    if( !fragment ) fragment = currentSlide.querySelector( '.fragment' );

                    var fragmentAutoSlide = fragment ? fragment.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. Not applicable if the slide
                    // is divided up into fragments. 
                    // playbackRate is accounted for in the duration.
                    if( currentSlide.querySelectorAll( '.fragment' ).length === 0 ) {
                            toArray( currentSlide.querySelectorAll( 'video, audio' ) ).forEach( function( el ) {
                                    if( el.hasAttribute( 'data-autoplay' ) ) {
                                            if( autoSlide && (el.duration * 1000 / el.playbackRate ) > autoSlide ) {
                                                    autoSlide = ( el.duration * 1000 / el.playbackRate ) + 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( function() {
                                    typeof config.autoSlideMethod === 'function' ? config.autoSlideMethod() : navigateNext();
                                    cueAutoSlide();
                            }, 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();
                    }
            }

    }

    /**
     * Checks if the target element prevents the triggering of
     * swipe navigation.
     */
    function isSwipePrevented( target ) {

            while( target && typeof target.hasAttribute === 'function' ) {
                    if( target.hasAttribute( 'data-prevent-swipe' ) ) return true;
                    target = target.parentNode;
            }

            return false;

    }

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

    /**
     * Called by all event handlers that are based on user
     * input.
     *
     * @param {object} [event]
     */
    function onUserInput( event ) {

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

    }

    /**
     * Handler for the document level 'keypress' event.
     *
     * @param {object} 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.
     *
     * @param {object} 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 );
            var activeElementIsNotes = document.activeElement && document.activeElement.className && /speaker-notes/i.test( document.activeElement.className);

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

            // While paused only allow resume keyboard events; 'b', 'v', '.'
            var resumeKeyCodes = [66,86,190,191];
            var key;

            // Custom key bindings for togglePause should be able to resume
            if( typeof config.keyboard === 'object' ) {
                    for( key in config.keyboard ) {
                            if( config.keyboard[key] === 'togglePause' ) {
                                    resumeKeyCodes.push( parseInt( key, 10 ) );
                            }
                    }
            }

            if( isPaused() && resumeKeyCodes.indexOf( event.keyCode ) === -1 ) {
                    return false;
            }

            var triggered = false;

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

                    for( 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, v, period, Logitech presenter tools "black screen" button
                            case 58: case 59: case 66: case 86: 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.
     *
     * @param {object} event
     */
    function onTouchStart( event ) {

            if( isSwipePrevented( event.target ) ) return true;

            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.
     *
     * @param {object} event
     */
    function onTouchMove( event ) {

            if( isSwipePrevented( event.target ) ) return true;

            // 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( UA.match( /android/gi ) ) {
                    event.preventDefault();
            }

    }

    /**
     * Handler for the 'touchend' event.
     *
     * @param {object} event
     */
    function onTouchEnd( event ) {

            touch.captured = false;

    }

    /**
     * Convert pointer down to touch start.
     *
     * @param {object} event
     */
    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.
     *
     * @param {object} event
     */
    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.
     *
     * @param {object} event
     */
    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.
     *
     * @param {object} event
     */
    function onDocumentMouseScroll( event ) {

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

                    lastMouseWheelStep = Date.now();

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

            }

    }

    /**
     * Clicking on the progress bar results in a navigation to the
     * closest approximate horizontal slide using this equation:
     *
     * ( clickX / presentationWidth ) * numberOfSlides
     *
     * @param {object} event
     */
    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.
     *
     * @param {object} [event]
     */
    function onWindowHashChange( event ) {

            readURL();

    }

    /**
     * Handler for the window level 'resize' event.
     *
     * @param {object} [event]
     */
    function onWindowResize( event ) {

            layout();

    }

    /**
     * Handle for the window level 'visibilitychange' event.
     *
     * @param {object} [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.
     *
     * @param {object} event
     */
    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.
     *
     * @param {object} event
     */
    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.
     *
     * @param {object} [event]
     */
    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 = 100;
            this.diameter2 = this.diameter/2;
            this.thickness = 6;

            // 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.canvas.style.width = this.diameter2 + 'px';
            this.canvas.style.height = this.diameter2 + 'px';
            this.context = this.canvas.getContext( '2d' );

            this.container.appendChild( this.canvas );

            this.render();

    }

    /**
     * @param value
     */
    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.diameter2 ) - this.thickness,
                    x = this.diameter2,
                    y = this.diameter2,
                    iconSize = 28;

            // 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 + 4, 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 - 4, iconSize );
                    this.context.fillRect( iconSize / 2 + 4, 0, iconSize / 2 - 4, iconSize );
            }
            else {
                    this.context.beginPath();
                    this.context.translate( 4, 0 );
                    this.context.moveTo( 0, 0 );
                    this.context.lineTo( iconSize - 4, 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 = {
            VERSION: VERSION,

            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,

            // Shows a help overlay with keyboard shortcuts
            showHelp: showHelp,

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

            // Randomizes the order of slides
            shuffle: shuffle,

            // 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 speaker notes string for a slide, or null
            getSlideNotes: getSlideNotes,

            // 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 } );
            },

            // Registers a new shortcut to include in the help overlay
            registerKeyboardShortcut: function( key, value ) {
                    keyboardShortcuts[key] = value;
            }
    };

    return Reveal;

}));