hakimel/reveal.js

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js/reveal.js

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import SlideContent from './controllers/slidecontent.js'
import SlideNumber from './controllers/slidenumber.js'
import JumpToSlide from './controllers/jumptoslide.js'
import Backgrounds from './controllers/backgrounds.js'
import AutoAnimate from './controllers/autoanimate.js'
import ScrollView from './controllers/scrollview.js'
import PrintView from './controllers/printview.js'
import Fragments from './controllers/fragments.js'
import Overview from './controllers/overview.js'
import Keyboard from './controllers/keyboard.js'
import Location from './controllers/location.js'
import Controls from './controllers/controls.js'
import Progress from './controllers/progress.js'
import Pointer from './controllers/pointer.js'
import Plugins from './controllers/plugins.js'
import Touch from './controllers/touch.js'
import Focus from './controllers/focus.js'
import Notes from './controllers/notes.js'
import Playback from './components/playback.js'
import defaultConfig from './config.js'
import * as Util from './utils/util.js'
import * as Device from './utils/device.js'
import {
    SLIDES_SELECTOR,
    HORIZONTAL_SLIDES_SELECTOR,
    VERTICAL_SLIDES_SELECTOR,
    POST_MESSAGE_METHOD_BLACKLIST
} from './utils/constants.js'

// The reveal.js version
export const VERSION = '5.1.0';

/**
 * reveal.js
 * https://revealjs.com
 * MIT licensed
 *
 * Copyright (C) 2011-2022 Hakim El Hattab, https://hakim.se
 */
export default function( revealElement, options ) {

    // Support initialization with no args, one arg
    // [options] or two args [revealElement, options]
    if( arguments.length < 2 ) {
        options = arguments[0];
        revealElement = document.querySelector( '.reveal' );
    }

    const Reveal = {};

    // Configuration defaults, can be overridden at initialization time
    let config = {},

        // Flags if initialize() has been invoked for this reveal instance
        initialized = false,

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

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

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

        // Remember which directions that the user has navigated towards
        navigationHistory = {
            hasNavigatedHorizontally: false,
            hasNavigatedVertically: false
        },

        // Slides may have 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 = {},

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

        // The current slide transition state; idle or running
        transition = 'idle',

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

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

        // Controllers for different aspects of our presentation. They're
        // all given direct references to this Reveal instance since there
        // may be multiple presentations running in parallel.
        slideContent = new SlideContent( Reveal ),
        slideNumber = new SlideNumber( Reveal ),
        jumpToSlide = new JumpToSlide( Reveal ),
        autoAnimate = new AutoAnimate( Reveal ),
        backgrounds = new Backgrounds( Reveal ),
        scrollView = new ScrollView( Reveal ),
        printView = new PrintView( Reveal ),
        fragments = new Fragments( Reveal ),
        overview = new Overview( Reveal ),
        keyboard = new Keyboard( Reveal ),
        location = new Location( Reveal ),
        controls = new Controls( Reveal ),
        progress = new Progress( Reveal ),
        pointer = new Pointer( Reveal ),
        plugins = new Plugins( Reveal ),
        focus = new Focus( Reveal ),
        touch = new Touch( Reveal ),
        notes = new Notes( Reveal );

    /**
     * Starts up the presentation.
     */
    function initialize( initOptions ) {

        if( !revealElement ) throw 'Unable to find presentation root (<div class="reveal">).';

        initialized = true;

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

        if( !dom.slides ) throw 'Unable to find slides container (<div class="slides">).';

        // Compose our config object in order of increasing precedence:
        // 1. Default reveal.js options
        // 2. Options provided via Reveal.configure() prior to
        //    initialization
        // 3. Options passed to the Reveal constructor
        // 4. Options passed to Reveal.initialize
        // 5. Query params
        config = { ...defaultConfig, ...config, ...options, ...initOptions, ...Util.getQueryHash() };

        // Legacy support for the ?print-pdf query
        if( /print-pdf/gi.test( window.location.search ) ) {
            config.view = 'print';
        }

        setViewport();

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

        // Register plugins and load dependencies, then move on to #start()
        plugins.load( config.plugins, config.dependencies ).then( start );

        return new Promise( resolve => Reveal.on( 'ready', resolve ) );

    }

    /**
     * Encase the presentation in a reveal.js viewport. The
     * extent of the viewport differs based on configuration.
     */
    function setViewport() {

        // Embedded decks use the reveal element as their viewport
        if( config.embedded === true ) {
            dom.viewport = Util.closest( revealElement, '.reveal-viewport' ) || revealElement;
        }
        // Full-page decks use the body as their viewport
        else {
            dom.viewport = document.body;
            document.documentElement.classList.add( 'reveal-full-page' );
        }

        dom.viewport.classList.add( 'reveal-viewport' );

    }

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

        // Don't proceed if this instance has been destroyed
        if( initialized === false ) return;

        ready = true;

        // Remove slides hidden with data-visibility
        removeHiddenSlides();

        // 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();

        // Adds bindings for fullscreen mode
        setupFullscreen();

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

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

        // Create slide backgrounds
        backgrounds.update( true );

        // Activate the print/scroll view if configured
        activateInitialView();

        // Read the initial hash
        location.readURL();

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

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

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

    }

    /**
     * Activates the correct reveal.js view based on our config.
     * This is only invoked once during initialization.
     */
    function activateInitialView() {

        const activatePrintView = config.view === 'print';
        const activateScrollView = config.view === 'scroll' || config.view === 'reader';

        if( activatePrintView || activateScrollView ) {

            if( activatePrintView ) {
                removeEventListeners();
            }
            else {
                touch.unbind();
            }

            // Avoid content flickering during layout
            dom.viewport.classList.add( 'loading-scroll-mode' );

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

    }

    /**
     * Removes all slides with data-visibility="hidden". This
     * is done right before the rest of the presentation is
     * initialized.
     *
     * If you want to show all hidden slides, initialize
     * reveal.js with showHiddenSlides set to true.
     */
    function removeHiddenSlides() {

        if( !config.showHiddenSlides ) {
            Util.queryAll( dom.wrapper, 'section[data-visibility="hidden"]' ).forEach( slide => {
                const parent = slide.parentNode;

                // If this slide is part of a stack and that stack will be
                // empty after removing the hidden slide, remove the entire
                // stack
                if( parent.childElementCount === 1 && /section/i.test( parent.nodeName ) ) {
                    parent.remove();
                }
                else {
                    slide.remove();
                }

            } );
        }

    }

    /**
     * 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' );

        if( Device.isMobile ) {
            dom.wrapper.classList.add( 'no-hover' );
        }
        else {
            dom.wrapper.classList.remove( 'no-hover' );
        }

        backgrounds.render();
        slideNumber.render();
        jumpToSlide.render();
        controls.render();
        progress.render();
        notes.render();

        // Overlay graphic which is displayed during the paused mode
        dom.pauseOverlay = Util.createSingletonNode( dom.wrapper, 'div', 'pause-overlay', config.controls ? '<button class="resume-button">Resume presentation</button>' : null );

        dom.statusElement = createStatusElement();

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

    /**
     * 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 createStatusElement() {

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

    }

    /**
     * Announces the given text to screen readers.
     */
    function announceStatus( value ) {

        dom.statusElement.textContent = value;

    }

    /**
     * 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 ) {

        let text = '';

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

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

                Array.from( node.childNodes ).forEach( child => {
                    text += getStatusText( child );
                } );

            }

        }

        text = text.trim();

        return text === '' ? '' : text + ' ';

    }

    /**
     * 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( () => {
            if( !scrollView.isActive() && dom.wrapper.scrollTop !== 0 || dom.wrapper.scrollLeft !== 0 ) {
                dom.wrapper.scrollTop = 0;
                dom.wrapper.scrollLeft = 0;
            }
        }, 1000 );

    }

    /**
     * After entering fullscreen we need to force a layout to
     * get our presentations to scale correctly. This behavior
     * is inconsistent across browsers but a force layout seems
     * to normalize it.
     */
    function setupFullscreen() {

        document.addEventListener( 'fullscreenchange', onFullscreenChange );
        document.addEventListener( 'webkitfullscreenchange', onFullscreenChange );

    }

    /**
     * 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', onPostMessage, false );
        }

    }

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

        const oldConfig = { ...config }

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

        // Abort if reveal.js hasn't finished loading, config
        // changes will be applied automatically once ready
        if( Reveal.isReady() ===  false ) return;

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

        // The transition is added as a class on the .reveal element
        dom.wrapper.classList.remove( oldConfig.transition );
        dom.wrapper.classList.add( config.transition );

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

        // Expose our configured slide dimensions as custom props
        dom.viewport.style.setProperty( '--slide-width', typeof config.width === 'string' ? config.width :  config.width + 'px' );
        dom.viewport.style.setProperty( '--slide-height', typeof config.height === 'string' ? config.height :  config.height + 'px' );

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

        Util.toggleClass( dom.wrapper, 'embedded', config.embedded );
        Util.toggleClass( dom.wrapper, 'rtl', config.rtl );
        Util.toggleClass( dom.wrapper, 'center', config.center );

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

        // Iframe link previews
        if( config.previewLinks ) {
            enablePreviewLinks();
            disablePreviewLinks( '[data-preview-link=false]' );
        }
        else {
            disablePreviewLinks();
            enablePreviewLinks( '[data-preview-link]:not([data-preview-link=false])' );
        }

        // Reset all changes made by auto-animations
        autoAnimate.reset();

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

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

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

        // Add the navigation mode to the DOM so we can adjust styling
        if( config.navigationMode !== 'default' ) {
            dom.wrapper.setAttribute( 'data-navigation-mode', config.navigationMode );
        }
        else {
            dom.wrapper.removeAttribute( 'data-navigation-mode' );
        }

        notes.configure( config, oldConfig );
        focus.configure( config, oldConfig );
        pointer.configure( config, oldConfig );
        controls.configure( config, oldConfig );
        progress.configure( config, oldConfig );
        keyboard.configure( config, oldConfig );
        fragments.configure( config, oldConfig );
        slideNumber.configure( config, oldConfig );

        sync();

    }

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

        eventsAreBound = true;

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

        if( config.touch ) touch.bind();
        if( config.keyboard ) keyboard.bind();
        if( config.progress ) progress.bind();
        if( config.respondToHashChanges ) location.bind();
        controls.bind();
        focus.bind();

        dom.slides.addEventListener( 'click', onSlidesClicked, false );
        dom.slides.addEventListener( 'transitionend', onTransitionEnd, false );
        dom.pauseOverlay.addEventListener( 'click', resume, false );

        if( config.focusBodyOnPageVisibilityChange ) {
            document.addEventListener( 'visibilitychange', onPageVisibilityChange, false );
        }

    }

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

        eventsAreBound = false;

        touch.unbind();
        focus.unbind();
        keyboard.unbind();
        controls.unbind();
        progress.unbind();
        location.unbind();

        window.removeEventListener( 'resize', onWindowResize, false );

        dom.slides.removeEventListener( 'click', onSlidesClicked, false );
        dom.slides.removeEventListener( 'transitionend', onTransitionEnd, false );
        dom.pauseOverlay.removeEventListener( 'click', resume, false );

    }

    /**
     * Uninitializes reveal.js by undoing changes made to the
     * DOM and removing all event listeners.
     */
    function destroy() {

        initialized = false;

        // There's nothing to destroy if this instance hasn't finished
        // initializing
        if( ready === false ) return;

        removeEventListeners();
        cancelAutoSlide();
        disablePreviewLinks();

        // Destroy controllers
        notes.destroy();
        focus.destroy();
        plugins.destroy();
        pointer.destroy();
        controls.destroy();
        progress.destroy();
        backgrounds.destroy();
        slideNumber.destroy();
        jumpToSlide.destroy();

        // Remove event listeners
        document.removeEventListener( 'fullscreenchange', onFullscreenChange );
        document.removeEventListener( 'webkitfullscreenchange', onFullscreenChange );
        document.removeEventListener( 'visibilitychange', onPageVisibilityChange, false );
        window.removeEventListener( 'message', onPostMessage, false );
        window.removeEventListener( 'load', layout, false );

        // Undo DOM changes
        if( dom.pauseOverlay ) dom.pauseOverlay.remove();
        if( dom.statusElement ) dom.statusElement.remove();

        document.documentElement.classList.remove( 'reveal-full-page' );

        dom.wrapper.classList.remove( 'ready', 'center', 'has-horizontal-slides', 'has-vertical-slides' );
        dom.wrapper.removeAttribute( 'data-transition-speed' );
        dom.wrapper.removeAttribute( 'data-background-transition' );

        dom.viewport.classList.remove( 'reveal-viewport' );
        dom.viewport.style.removeProperty( '--slide-width' );
        dom.viewport.style.removeProperty( '--slide-height' );

        dom.slides.style.removeProperty( 'width' );
        dom.slides.style.removeProperty( 'height' );
        dom.slides.style.removeProperty( 'zoom' );
        dom.slides.style.removeProperty( 'left' );
        dom.slides.style.removeProperty( 'top' );
        dom.slides.style.removeProperty( 'bottom' );
        dom.slides.style.removeProperty( 'right' );
        dom.slides.style.removeProperty( 'transform' );

        Array.from( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) ).forEach( slide => {
            slide.style.removeProperty( 'display' );
            slide.style.removeProperty( 'top' );
            slide.removeAttribute( 'hidden' );
            slide.removeAttribute( 'aria-hidden' );
        } );

    }

    /**
     * Adds a listener to one of our custom reveal.js events,
     * like slidechanged.
     */
    function on( type, listener, useCapture ) {

        revealElement.addEventListener( type, listener, useCapture );

    }

    /**
     * Unsubscribes from a reveal.js event.
     */
    function off( type, listener, useCapture ) {

        revealElement.removeEventListener( type, listener, useCapture );

    }

    /**
     * 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 ) {
            Util.transformElement( dom.slides, slidesTransform.layout + ' ' + slidesTransform.overview );
        }
        else {
            Util.transformElement( dom.slides, slidesTransform.overview );
        }

    }

    /**
     * Dispatches an event of the specified type from the
     * reveal DOM element.
     */
    function dispatchEvent({ target=dom.wrapper, type, data, bubbles=true }) {

        let event = document.createEvent( 'HTMLEvents', 1, 2 );
        event.initEvent( type, bubbles, true );
        Util.extend( event, data );
        target.dispatchEvent( event );

        if( target === dom.wrapper ) {
            // If we're in an iframe, post each reveal.js event to the
            // parent window. Used by the notes plugin
            dispatchPostMessage( type );
        }

        return event;

    }

    /**
     * Dispatches a slidechanged event.
     *
     * @param {string} origin Used to identify multiplex clients
     */
    function dispatchSlideChanged( origin ) {

        dispatchEvent({
            type: 'slidechanged',
            data: {
                indexh,
                indexv,
                previousSlide,
                currentSlide,
                origin
            }
        });

    }

    /**
     * Dispatched a postMessage of the given type from our window.
     */
    function dispatchPostMessage( type, data ) {

        if( config.postMessageEvents && window.parent !== window.self ) {
            let message = {
                namespace: 'reveal',
                eventName: type,
                state: getState()
            };

            Util.extend( message, data );

            window.parent.postMessage( JSON.stringify( message ), '*' );
        }

    }

    /**
     * Bind preview frame links.
     *
     * @param {string} [selector=a] - selector for anchors
     */
    function enablePreviewLinks( selector = 'a' ) {

        Array.from( dom.wrapper.querySelectorAll( selector ) ).forEach( element => {
            if( /^(http|www)/gi.test( element.getAttribute( 'href' ) ) ) {
                element.addEventListener( 'click', onPreviewLinkClicked, false );
            }
        } );

    }

    /**
     * Unbind preview frame links.
     */
    function disablePreviewLinks( selector = 'a' ) {

        Array.from( dom.wrapper.querySelectorAll( selector ) ).forEach( 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>`;

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

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

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

    }

    /**
     * Open or close help overlay window.
     *
     * @param {Boolean} [override] Flag which overrides the
     * toggle logic and forcibly sets the desired state. True means
     * help is open, false means it's closed.
     */
    function toggleHelp( override ){

        if( typeof override === 'boolean' ) {
            override ? showHelp() : closeOverlay();
        }
        else {
            if( dom.overlay ) {
                closeOverlay();
            }
            else {
                showHelp();
            }
        }
    }

    /**
     * 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 );

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

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

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

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

            html += '</table>';

            dom.overlay.innerHTML = `
                <header>
                    <a class="close" href="#"><span class="icon"></span></a>
                </header>
                <div class="viewport">
                    <div class="viewport-inner">${html}</div>
                </div>
            `;

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

        }

    }

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

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

        return false;

    }

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

        if( dom.wrapper && !printView.isActive() ) {

            const viewportWidth = dom.viewport.offsetWidth;
            const viewportHeight = dom.viewport.offsetHeight;

            if( !config.disableLayout ) {

                // On some mobile devices '100vh' is taller than the visible
                // viewport which leads to part of the presentation being
                // cut off. To work around this we define our own '--vh' custom
                // property where 100x adds up to the correct height.
                //
                // https://css-tricks.com/the-trick-to-viewport-units-on-mobile/
                if( Device.isMobile && !config.embedded ) {
                    document.documentElement.style.setProperty( '--vh', ( window.innerHeight * 0.01 ) + 'px' );
                }

                const size = scrollView.isActive() ?
                             getComputedSlideSize( viewportWidth, viewportHeight ) :
                             getComputedSlideSize();

                const oldScale = scale;

                // 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 or we're
                // in the scroll view
                if( scale === 1 || scrollView.isActive() ) {
                    dom.slides.style.zoom = '';
                    dom.slides.style.left = '';
                    dom.slides.style.top = '';
                    dom.slides.style.bottom = '';
                    dom.slides.style.right = '';
                    transformSlides( { layout: '' } );
                }
                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
                const slides = Array.from( dom.wrapper.querySelectorAll( SLIDES_SELECTOR ) );

                for( let i = 0, len = slides.length; i < len; i++ ) {
                    const 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 = '';
                    }

                }

                if( oldScale !== scale ) {
                    dispatchEvent({
                        type: 'resize',
                        data: {
                            oldScale,
                            scale,
                            size
                        }
                    });
                }
            }

            checkResponsiveScrollView();

            dom.viewport.style.setProperty( '--slide-scale', scale );
            dom.viewport.style.setProperty( '--viewport-width', viewportWidth + 'px' );
            dom.viewport.style.setProperty( '--viewport-height', viewportHeight + 'px' );

            scrollView.layout();

            progress.update();
            backgrounds.updateParallax();

            if( overview.isActive() ) {
                overview.update();
            }

        }

    }

    /**
     * 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 'r-stretch' class
        Util.queryAll( dom.slides, 'section > .stretch, section > .r-stretch' ).forEach( element => {

            // Determine how much vertical space we can use
            let remainingHeight = Util.getRemainingHeight( element, height );

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

                const 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';
            }

        } );

    }

    /**
     * Responsively activates the scroll mode when we reach the configured
     * activation width.
     */
    function checkResponsiveScrollView() {

        // Only proceed if...
        // 1. The DOM is ready
        // 2. Layouts aren't disabled via config
        // 3. We're not currently printing
        // 4. There is a scrollActivationWidth set
        // 5. The deck isn't configured to always use the scroll view
        if(
            dom.wrapper &&
            !config.disableLayout &&
            !printView.isActive() &&
            typeof config.scrollActivationWidth === 'number' &&
            config.view !== 'scroll'
        ) {
            const size = getComputedSlideSize();

            if( size.presentationWidth > 0 && size.presentationWidth <= config.scrollActivationWidth ) {
                if( !scrollView.isActive() ) {
                    backgrounds.create();
                    scrollView.activate()
                };
            }
            else {
                if( scrollView.isActive() ) scrollView.deactivate();
            }
        }

    }

    /**
     * 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 ) {

        let width = config.width;
        let height = config.height;

        if( config.disableLayout ) {
            width = dom.slides.offsetWidth;
            height = dom.slides.offsetHeight;
        }

        const size = {
            // Slide size
            width: width,
            height: 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
            const attributeName = stack.hasAttribute( 'data-start-indexv' ) ? 'data-start-indexv' : 'data-previous-indexv';

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

        return 0;

    }

    /**
     * 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 = currentSlide ) {

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

    }

    /**
     * Checks if the current or specified slide is a stack containing
     * vertical slides.
     *
     * @param {HTMLElement} [slide=currentSlide]
     * @return {Boolean}
     */
    function isVerticalStack( slide = currentSlide ) {

        return slide.classList.contains( '.stack' ) || slide.querySelector( 'section' ) !== null;

    }

    /**
     * Returns true if we're on the last slide in the current
     * vertical stack.
     */
    function isLastVerticalSlide() {

        if( currentSlide && isVerticalSlide( currentSlide ) ) {
            // Does this slide have a next sibling?
            if( currentSlide.nextElementSibling ) return false;

            return true;
        }

        return false;

    }

    /**
     * Returns true if we're currently on the first slide in
     * the presentation.
     */
    function isFirstSlide() {

        return indexh === 0 && indexv === 0;

    }

    /**
     * Returns true if we're currently on the last slide in
     * the presentation. If the last slide is a stack, we only
     * consider this the last slide if it's at the end of the
     * stack.
     */
    function isLastSlide() {

        if( currentSlide ) {
            // Does this slide have a next 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;

    }

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

        if( config.pause ) {
            const wasPaused = dom.wrapper.classList.contains( 'paused' );

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

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

    }

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

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

        cueAutoSlide();

        if( wasPaused ) {
            dispatchEvent({ type: '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 visibility of the jump-to-slide UI.
     */
    function toggleJumpToSlide( override ) {

        if( typeof override === 'boolean' ) {
            override ? jumpToSlide.show() : jumpToSlide.hide();
        }
        else {
            jumpToSlide.isVisible() ? jumpToSlide.hide() : jumpToSlide.show();
        }

    }

    /**
     * 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} [origin] Origin for use in multimaster environments
     */
    function slide( h, v, f, origin ) {

        // Dispatch an event before the slide
        const slidechange = dispatchEvent({
            type: 'beforeslidechange',
            data: {
                indexh: h === undefined ? indexh : h,
                indexv: v === undefined ? indexv : v,
                origin
            }
        });

        // Abort if this slide change was prevented by an event listener
        if( slidechange.defaultPrevented ) return;

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

        // Query all horizontal slides in the deck
        const horizontalSlides = dom.wrapper.querySelectorAll( HORIZONTAL_SLIDES_SELECTOR );

        // If we're in scroll mode, we scroll the target slide into view
        // instead of running our standard slide transition
        if( scrollView.isActive() ) {
            const scrollToSlide = scrollView.getSlideByIndices( h, v );
            if( scrollToSlide ) scrollView.scrollToSlide( scrollToSlide );
            return;
        }

        // 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 && !overview.isActive() ) {
            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
        const stateBefore = state.concat();

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

        let 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 );

        // Dispatch an event if the slide changed
        let slideChanged = ( indexh !== indexhBefore || indexv !== indexvBefore );

        // Ensure that the previous slide is never the same as the current
        if( !slideChanged ) previousSlide = null;

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

        // Indicate when we're on a vertical slide
        revealElement.classList.toggle( 'is-vertical-slide', currentVerticalSlides.length > 1 );

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

        let autoAnimateTransition = false;

        // Detect if we're moving between two auto-animated slides
        if( slideChanged && previousSlide && currentSlide && !overview.isActive() ) {
            transition = 'running';

            autoAnimateTransition = shouldAutoAnimateBetween( previousSlide, currentSlide, indexhBefore, indexvBefore );

            // If this is an auto-animated transition, we disable the
            // regular slide transition
            //
            // Note 20-03-2020:
            // This needs to happen before we update slide visibility,
            // otherwise transitions will still run in Safari.
            if( autoAnimateTransition ) {
                dom.slides.classList.add( 'disable-slide-transitions' )
            }
        }

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

        layout();

        // Update the overview if it's currently active
        if( overview.isActive() ) {
            overview.update();
        }

        // Show fragment, if specified
        if( typeof f !== 'undefined' ) {
            fragments.goto( f );
        }

        // Solves an edge case where the previous slide maintains the
        // 'present' class when navigating between adjacent vertical
        // stacks
        if( previousSlide && previousSlide !== currentSlide ) {
            previousSlide.classList.remove( 'present' );
            previousSlide.setAttribute( 'aria-hidden', 'true' );

            // Reset all slides upon navigate to home
            if( isFirstSlide() ) {
                // Launch async task
                setTimeout( () => {
                    getVerticalStacks().forEach( slide => {
                        setPreviousVerticalIndex( slide, 0 );
                    } );
                }, 0 );
            }
        }

        // Apply the new state
        stateLoop: for( let 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( let j = 0; j < stateBefore.length; j++ ) {
                if( stateBefore[j] === state[i] ) {
                    stateBefore.splice( j, 1 );
                    continue stateLoop;
                }
            }

            dom.viewport.classList.add( state[i] );

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

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

        if( slideChanged ) {
            dispatchSlideChanged( origin );
        }

        // Handle embedded content
        if( slideChanged || !previousSlide ) {
            slideContent.stopEmbeddedContent( previousSlide );
            slideContent.startEmbeddedContent( currentSlide );
        }

        // Announce the current slide contents to screen readers
        // Use animation frame to prevent getComputedStyle in getStatusText
        // from triggering layout mid-frame
        requestAnimationFrame( () => {
            announceStatus( getStatusText( currentSlide ) );
        });

        progress.update();
        controls.update();
        notes.update();
        backgrounds.update();
        backgrounds.updateParallax();
        slideNumber.update();
        fragments.update();

        // Update the URL hash
        location.writeURL();

        cueAutoSlide();

        // Auto-animation
        if( autoAnimateTransition ) {

            setTimeout( () => {
                dom.slides.classList.remove( 'disable-slide-transitions' );
            }, 0 );

            if( config.autoAnimate ) {
                // Run the auto-animation between our slides
                autoAnimate.run( previousSlide, currentSlide );
            }

        }

    }

    /**
     * Checks whether or not an auto-animation should take place between
     * the two given slides.
     *
     * @param {HTMLElement} fromSlide
     * @param {HTMLElement} toSlide
     * @param {number} indexhBefore
     * @param {number} indexvBefore
     *
     * @returns {boolean}
     */
    function shouldAutoAnimateBetween( fromSlide, toSlide, indexhBefore, indexvBefore ) {

        return     fromSlide.hasAttribute( 'data-auto-animate' ) && toSlide.hasAttribute( 'data-auto-animate' ) &&
                fromSlide.getAttribute( 'data-auto-animate-id' ) === toSlide.getAttribute( 'data-auto-animate-id' ) &&
                !( ( indexh > indexhBefore || indexv > indexvBefore ) ? toSlide : fromSlide ).hasAttribute( 'data-auto-animate-restart' );

    }

    /**
     * Called anytime a new slide should be activated while in the scroll
     * view. The active slide is the page that occupies the most space in
     * the scrollable viewport.
     *
     * @param {number} pageIndex
     * @param {HTMLElement} slideElement
     */
    function setCurrentScrollPage( slideElement, h, v ) {

        let indexhBefore = indexh || 0;

        indexh = h;
        indexv = v;

        const slideChanged = currentSlide !== slideElement;

        previousSlide = currentSlide;
        currentSlide = slideElement;

        if( currentSlide && previousSlide ) {
            if( config.autoAnimate && shouldAutoAnimateBetween( previousSlide, currentSlide, indexhBefore, indexv ) ) {
                // Run the auto-animation between our slides
                autoAnimate.run( previousSlide, currentSlide );
            }
        }

        // Start or stop embedded content like videos and iframes
        if( slideChanged ) {
            if( previousSlide ) {
                slideContent.stopEmbeddedContent( previousSlide );
                slideContent.stopEmbeddedContent( previousSlide.slideBackgroundElement );
            }

            slideContent.startEmbeddedContent( currentSlide );
            slideContent.startEmbeddedContent( currentSlide.slideBackgroundElement );
        }

        requestAnimationFrame( () => {
            announceStatus( getStatusText( currentSlide ) );
        });

        dispatchSlideChanged();

    }

    /**
     * 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 all slide backgrounds
        backgrounds.create();

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

        if( config.sortFragmentsOnSync === true ) {
            fragments.sortAll();
        }

        controls.update();
        progress.update();

        updateSlidesVisibility();

        notes.update();
        notes.updateVisibility();
        backgrounds.update( true );
        slideNumber.update();
        slideContent.formatEmbeddedContent();

        // Start or stop embedded content depending on global config
        if( config.autoPlayMedia === false ) {
            slideContent.stopEmbeddedContent( currentSlide, { unloadIframes: false } );
        }
        else {
            slideContent.startEmbeddedContent( currentSlide );
        }

        if( overview.isActive() ) {
            overview.layout();
        }

    }

    /**
     * Updates reveal.js to keep in sync with new slide attributes. For
     * example, if you add a new `data-background-image` you can call
     * this to have reveal.js render the new background image.
     *
     * Similar to #sync() but more efficient when you only need to
     * refresh a specific slide.
     *
     * @param {HTMLElement} slide
     */
    function syncSlide( slide = currentSlide ) {

        backgrounds.sync( slide );
        fragments.sync( slide );

        slideContent.load( slide );

        backgrounds.update();
        notes.update();

    }

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

        getHorizontalSlides().forEach( horizontalSlide => {

            Util.queryAll( horizontalSlide, 'section' ).forEach( ( verticalSlide, y ) => {

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

            } );

        } );

    }

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

        slides.forEach( ( slide, i ) => {

            // Insert the slide next to a randomly picked sibling slide
            // slide. This may cause the slide to insert before itself,
            // but that's not an issue.
            let beforeSlide = slides[ Math.floor( Math.random() * slides.length ) ];
            if( beforeSlide.parentNode === slide.parentNode ) {
                slide.parentNode.insertBefore( slide, beforeSlide );
            }

            // Randomize the order of vertical slides (if there are any)
            let verticalSlides = slide.querySelectorAll( 'section' );
            if( verticalSlides.length ) {
                shuffle( verticalSlides );
            }

        } );

    }

    /**
     * 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
        let slides = Util.queryAll( dom.wrapper, selector ),
            slidesLength = slides.length;

        let printMode = scrollView.isActive() || printView.isActive();
        let loopedForwards = false;
        let loopedBackwards = false;

        if( slidesLength ) {

            // Should the index loop?
            if( config.loop ) {
                if( index >= slidesLength ) loopedForwards = true;

                index %= slidesLength;

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

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

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

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

                // Avoid .remove() with multiple args for IE11 support
                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 ) {
                        // Show all fragments in prior slides
                        showFragmentsIn( element );
                    }
                }
                else if( i > index ) {
                    // Any element subsequent to index is given the 'future' class
                    element.classList.add( reverse ? 'past' : 'future' );

                    if( config.fragments ) {
                        // Hide all fragments in future slides
                        hideFragmentsIn( element );
                    }
                }
                // Update the visibility of fragments when a presentation loops
                // in either direction
                else if( i === index && config.fragments ) {
                    if( loopedForwards ) {
                        hideFragmentsIn( element );
                    }
                    else if( loopedBackwards ) {
                        showFragmentsIn( element );
                    }
                }
            }

            let slide = slides[index];
            let wasPresent = slide.classList.contains( 'present' );

            // Mark the current slide as present
            slide.classList.add( 'present' );
            slide.removeAttribute( 'hidden' );
            slide.removeAttribute( 'aria-hidden' );

            if( !wasPresent ) {
                // Dispatch an event indicating the slide is now visible
                dispatchEvent({
                    target: slide,
                    type: 'visible',
                    bubbles: false
                });
            }

            // If this slide has a state associated with it, add it
            // onto the current state of the deck
            let slideState = slide.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;

    }

    /**
     * Shows all fragment elements within the given container.
     */
    function showFragmentsIn( container ) {

        Util.queryAll( container, '.fragment' ).forEach( fragment => {
            fragment.classList.add( 'visible' );
            fragment.classList.remove( 'current-fragment' );
        } );

    }

    /**
     * Hides all fragment elements within the given container.
     */
    function hideFragmentsIn( container ) {

        Util.queryAll( container, '.fragment.visible' ).forEach( fragment => {
            fragment.classList.remove( 'visible', 'current-fragment' );
        } );

    }

    /**
     * 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
        let horizontalSlides = getHorizontalSlides(),
            horizontalSlidesLength = horizontalSlides.length,
            distanceX,
            distanceY;

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

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

            // Shorten the view distance on devices that typically have
            // less resources
            if( Device.isMobile ) {
                viewDistance = overview.isActive() ? 6 : config.mobileViewDistance;
            }

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

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

                let verticalSlides = Util.queryAll( horizontalSlide, '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 ) {
                    slideContent.load( horizontalSlide );
                }
                else {
                    slideContent.unload( horizontalSlide );
                }

                if( verticalSlidesLength ) {

                    let oy = getPreviousVerticalIndex( horizontalSlide );

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

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

                        if( distanceX + distanceY < viewDistance ) {
                            slideContent.load( verticalSlide );
                        }
                        else {
                            slideContent.unload( verticalSlide );
                        }
                    }

                }
            }

            // Flag if there are ANY vertical slides, anywhere in the deck
            if( hasVerticalSlides() ) {
                dom.wrapper.classList.add( 'has-vertical-slides' );
            }
            else {
                dom.wrapper.classList.remove( 'has-vertical-slides' );
            }

            // Flag if there are ANY horizontal slides, anywhere in the deck
            if( hasHorizontalSlides() ) {
                dom.wrapper.classList.add( 'has-horizontal-slides' );
            }
            else {
                dom.wrapper.classList.remove( 'has-horizontal-slides' );
            }

        }

    }

    /**
     * Determine what available routes there are for navigation.
     *
     * @return {{left: boolean, right: boolean, up: boolean, down: boolean}}
     */
    function availableRoutes({ includeFragments = false } = {}) {

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

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

        // Looped presentations can always be navigated as long as
        // there are slides available
        if( config.loop ) {
            if( horizontalSlides.length > 1 ) {
                routes.left = true;
                routes.right = true;
            }

            if( verticalSlides.length > 1 ) {
                routes.up = true;
                routes.down = true;
            }
        }

        if ( horizontalSlides.length > 1 && config.navigationMode === 'linear' ) {
            routes.right = routes.right || routes.down;
            routes.left = routes.left || routes.up;
        }

        // If includeFragments is set, a route will be considered
        // available if either a slid OR fragment is available in
        // the given direction
        if( includeFragments === true ) {
            let fragmentRoutes = fragments.availableRoutes();
            routes.left = routes.left || fragmentRoutes.prev;
            routes.up = routes.up || fragmentRoutes.prev;
            routes.down = routes.down || fragmentRoutes.next;
            routes.right = routes.right || fragmentRoutes.next;
        }

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

        return routes;

    }

    /**
     * Returns the number of past slides. This can be used as a global
     * flattened index for slides.
     *
     * @param {HTMLElement} [slide=currentSlide] The slide we're counting before
     *
     * @return {number} Past slide count
     */
    function getSlidePastCount( slide = currentSlide ) {

        let horizontalSlides = getHorizontalSlides();

        // The number of past slides
        let pastCount = 0;

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

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

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

                // Stop as soon as we arrive at the present
                if( verticalSlides[j] === slide ) {
                    break mainLoop;
                }

                // Don't count slides with the "uncounted" class
                if( verticalSlides[j].dataset.visibility !== 'uncounted' ) {
                    pastCount++;
                }

            }

            // Stop as soon as we arrive at the present
            if( horizontalSlide === slide ) {
                break;
            }

            // Don't count the wrapping section for vertical slides and
            // slides marked as uncounted
            if( horizontalSlide.classList.contains( 'stack' ) === false && horizontalSlide.dataset.visibility !== 'uncounted' ) {
                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
        let totalCount = getTotalSlides();
        let pastCount = getSlidePastCount();

        if( currentSlide ) {

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

            // If there are fragments in the current slide those should be
            // accounted for in the progress.
            if( allFragments.length > 0 ) {
                let 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)
                let fragmentWeight = 0.9;

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

        }

        return Math.min( pastCount / ( totalCount - 1 ), 1 );

    }

    /**
     * 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
        let h = indexh,
            v = indexv,
            f;

        // If a slide is specified, return the indices of that slide
        if( slide ) {
            // In scroll mode the original h/x index is stored on the slide
            if( scrollView.isActive() ) {
                h = parseInt( slide.getAttribute( 'data-index-h' ), 10 );

                if( slide.getAttribute( 'data-index-v' ) ) {
                    v = parseInt( slide.getAttribute( 'data-index-v' ), 10 );
                }
            }
            else {
                let isVertical = isVerticalSlide( slide );
                let slideh = isVertical ? slide.parentNode : slide;

                // Select all horizontal slides
                let horizontalSlides = getHorizontalSlides();

                // 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( Util.queryAll( slide.parentNode, 'section' ).indexOf( slide ), 0 );
                }
            }
        }

        if( !slide && currentSlide ) {
            let hasFragments = currentSlide.querySelectorAll( '.fragment' ).length > 0;
            if( hasFragments ) {
                let 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, v, f };

    }

    /**
     * Retrieves all slides in this presentation.
     */
    function getSlides() {

        return Util.queryAll( dom.wrapper, SLIDES_SELECTOR + ':not(.stack):not([data-visibility="uncounted"])' );

    }

    /**
     * Returns a list of all horizontal slides in the deck. Each
     * vertical stack is included as one horizontal slide in the
     * resulting array.
     */
    function getHorizontalSlides() {

        return Util.queryAll( dom.wrapper, HORIZONTAL_SLIDES_SELECTOR );

    }

    /**
     * Returns all vertical slides that exist within this deck.
     */
    function getVerticalSlides() {

        return Util.queryAll( dom.wrapper, '.slides>section>section' );

    }

    /**
     * Returns all vertical stacks (each stack can contain multiple slides).
     */
    function getVerticalStacks() {

        return Util.queryAll( dom.wrapper, HORIZONTAL_SLIDES_SELECTOR + '.stack');

    }

    /**
     * Returns true if there are at least two horizontal slides.
     */
    function hasHorizontalSlides() {

        return getHorizontalSlides().length > 1;
    }

    /**
     * Returns true if there are at least two vertical slides.
     */
    function hasVerticalSlides() {

        return getVerticalSlides().length > 1;

    }

    /**
     * Returns an array of objects where each object represents the
     * attributes on its respective slide.
     */
    function getSlidesAttributes() {

        return getSlides().map( slide => {

            let attributes = {};
            for( let i = 0; i < slide.attributes.length; i++ ) {
                let attribute = slide.attributes[ i ];
                attributes[ attribute.name ] = attribute.value;
            }
            return attributes;

        } );

    }

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

        return getSlides().length;

    }

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

        let horizontalSlide = getHorizontalSlides()[ x ];
        let 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 {mixed} x Horizontal background index OR a slide
     * HTML element
     * @param {number} y Vertical background index
     * @return {(HTMLElement[]|*)}
     */
    function getSlideBackground( x, y ) {

        let slide = typeof x === 'number' ? getSlide( x, y ) : x;
        if( slide ) {
            return slide.slideBackgroundElement;
        }

        return undefined;

    }

    /**
     * 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() {

        let indices = getIndices();

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

    }

    /**
     * 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( Util.deserialize( state.indexh ), Util.deserialize( state.indexv ), Util.deserialize( state.indexf ) );

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

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

            if( typeof overviewFlag === 'boolean' && overviewFlag !== overview.isActive() ) {
                overview.toggle( overviewFlag );
            }
        }

    }

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

        cancelAutoSlide();

        if( currentSlide && config.autoSlide !== false ) {

            let fragment = currentSlide.querySelector( '.current-fragment[data-autoslide]' );

            let fragmentAutoSlide = fragment ? fragment.getAttribute( 'data-autoslide' ) : null;
            let parentAutoSlide = currentSlide.parentNode ? currentSlide.parentNode.getAttribute( 'data-autoslide' ) : null;
            let 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 ) {
                    Util.queryAll( currentSlide, 'video, audio' ).forEach( 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() && !overview.isActive() && ( !isLastSlide() || fragments.availableRoutes().next || config.loop === true ) ) {
                autoSlideTimeout = setTimeout( () => {
                    if( typeof config.autoSlideMethod === 'function' ) {
                        config.autoSlideMethod()
                    }
                    else {
                        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({ type: 'autoslidepaused' });
            clearTimeout( autoSlideTimeout );

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

    }

    function resumeAutoSlide() {

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

    }

    function navigateLeft({skipFragments=false}={}) {

        navigationHistory.hasNavigatedHorizontally = true;

        // Scroll view navigation is handled independently
        if( scrollView.isActive() ) return scrollView.prev();

        // Reverse for RTL
        if( config.rtl ) {
            if( ( overview.isActive() || skipFragments || fragments.next() === false ) && availableRoutes().left ) {
                slide( indexh + 1, config.navigationMode === 'grid' ? indexv : undefined );
            }
        }
        // Normal navigation
        else if( ( overview.isActive() || skipFragments || fragments.prev() === false ) && availableRoutes().left ) {
            slide( indexh - 1, config.navigationMode === 'grid' ? indexv : undefined );
        }

    }

    function navigateRight({skipFragments=false}={}) {

        navigationHistory.hasNavigatedHorizontally = true;

        // Scroll view navigation is handled independently
        if( scrollView.isActive() ) return scrollView.next();

        // Reverse for RTL
        if( config.rtl ) {
            if( ( overview.isActive() || skipFragments || fragments.prev() === false ) && availableRoutes().right ) {
                slide( indexh - 1, config.navigationMode === 'grid' ? indexv : undefined );
            }
        }
        // Normal navigation
        else if( ( overview.isActive() || skipFragments || fragments.next() === false ) && availableRoutes().right ) {
            slide( indexh + 1, config.navigationMode === 'grid' ? indexv : undefined );
        }

    }

    function navigateUp({skipFragments=false}={}) {

        // Scroll view navigation is handled independently
        if( scrollView.isActive() ) return scrollView.prev();

        // Prioritize hiding fragments
        if( ( overview.isActive() || skipFragments || fragments.prev() === false ) && availableRoutes().up ) {
            slide( indexh, indexv - 1 );
        }

    }

    function navigateDown({skipFragments=false}={}) {

        navigationHistory.hasNavigatedVertically = true;

        // Scroll view navigation is handled independently
        if( scrollView.isActive() ) return scrollView.next();

        // Prioritize revealing fragments
        if( ( overview.isActive() || skipFragments || fragments.next() === 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({skipFragments=false}={}) {

        // Scroll view navigation is handled independently
        if( scrollView.isActive() ) return scrollView.prev();

        // Prioritize revealing fragments
        if( skipFragments || fragments.prev() === false ) {
            if( availableRoutes().up ) {
                navigateUp({skipFragments});
            }
            else {
                // Fetch the previous horizontal slide, if there is one
                let previousSlide;

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

                // When going backwards and arriving on a stack we start
                // at the bottom of the stack
                if( previousSlide && previousSlide.classList.contains( 'stack' ) ) {
                    let v = ( previousSlide.querySelectorAll( 'section' ).length - 1 ) || undefined;
                    let h = indexh - 1;
                    slide( h, v );
                }
                else if( config.rtl ) {
                    navigateRight({skipFragments});
                }
                else {
                    navigateLeft({skipFragments});
                }
            }
        }

    }

    /**
     * The reverse of #navigatePrev().
     */
    function navigateNext({skipFragments=false}={}) {

        navigationHistory.hasNavigatedHorizontally = true;
        navigationHistory.hasNavigatedVertically = true;

        // Scroll view navigation is handled independently
        if( scrollView.isActive() ) return scrollView.next();

        // Prioritize revealing fragments
        if( skipFragments || fragments.next() === false ) {

            let routes = availableRoutes();

            // When looping is enabled `routes.down` is always available
            // so we need a separate check for when we've reached the
            // end of a stack and should move horizontally
            if( routes.down && routes.right && config.loop && isLastVerticalSlide() ) {
                routes.down = false;
            }

            if( routes.down ) {
                navigateDown({skipFragments});
            }
            else if( config.rtl ) {
                navigateLeft({skipFragments});
            }
            else {
                navigateRight({skipFragments});
            }
        }

    }


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

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

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

    }

    /**
    * Listener for post message events posted to this window.
    */
    function onPostMessage( event ) {

        let 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' ) {

                if( POST_MESSAGE_METHOD_BLACKLIST.test( data.method ) === false ) {

                    const result = Reveal[data.method].apply( Reveal, data.args );

                    // Dispatch a postMessage event with the returned value from
                    // our method invocation for getter functions
                    dispatchPostMessage( 'callback', { method: data.method, result: result } );

                }
                else {
                    console.warn( 'reveal.js: "'+ data.method +'" is is blacklisted from the postMessage API' );
                }

            }
        }

    }

    /**
     * Event listener for transition end on the current slide.
     *
     * @param {object} [event]
     */
    function onTransitionEnd( event ) {

        if( transition === 'running' && /section/gi.test( event.target.nodeName ) ) {
            transition = 'idle';
            dispatchEvent({
                type: 'slidetransitionend',
                data: { indexh, indexv, previousSlide, currentSlide }
            });
        }

    }

    /**
     * A global listener for all click events inside of the
     * .slides container.
     *
     * @param {object} [event]
     */
    function onSlidesClicked( event ) {

        const anchor = Util.closest( event.target, 'a[href^="#"]' );

        // If a hash link is clicked, we find the target slide
        // and navigate to it. We previously relied on 'hashchange'
        // for links like these but that prevented media with
        // audio tracks from playing in mobile browsers since it
        // wasn't considered a direct interaction with the document.
        if( anchor ) {
            const hash = anchor.getAttribute( 'href' );
            const indices = location.getIndicesFromHash( hash );

            if( indices ) {
                Reveal.slide( indices.h, indices.v, indices.f );
                event.preventDefault();
            }
        }

    }

    /**
     * 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 ) {

        // If, after clicking a link or similar and we're coming back,
        // focus the document.body to ensure we can use keyboard shortcuts
        if( document.hidden === 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();
        }

    }

    /**
     * Handler for the document level 'fullscreenchange' event.
     *
     * @param {object} [event]
     */
    function onFullscreenChange( event ) {

        let element = document.fullscreenElement || document.webkitFullscreenElement;
        if( element === dom.wrapper ) {
            event.stopImmediatePropagation();

            // Timeout to avoid layout shift in Safari
            setTimeout( () => {
                Reveal.layout();
                Reveal.focus.focus(); // focus.focus :'(
            }, 1 );
        }

    }

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

    }


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

    // The public reveal.js API
    const API = {
        VERSION,

        initialize,
        configure,
        destroy,

        sync,
        syncSlide,
        syncFragments: fragments.sync.bind( fragments ),

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

        // Navigation aliases
        navigateLeft, navigateRight, navigateUp, navigateDown, navigatePrev, navigateNext,

        // Fragment methods
        navigateFragment: fragments.goto.bind( fragments ),
        prevFragment: fragments.prev.bind( fragments ),
        nextFragment: fragments.next.bind( fragments ),

        // Event binding
        on,
        off,

        // Legacy event binding methods left in for backwards compatibility
        addEventListener: on,
        removeEventListener: off,

        // Forces an update in slide layout
        layout,

        // Randomizes the order of slides
        shuffle,

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

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

        // Toggles a help overlay with keyboard shortcuts
        toggleHelp,

        // Toggles the overview mode on/off
        toggleOverview: overview.toggle.bind( overview ),

        // Toggles the scroll view on/off
        toggleScrollView: scrollView.toggle.bind( scrollView ),

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

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

        // Toggles visibility of the jump-to-slide UI
        toggleJumpToSlide,

        // Slide navigation checks
        isFirstSlide,
        isLastSlide,
        isLastVerticalSlide,
        isVerticalSlide,
        isVerticalStack,

        // State checks
        isPaused,
        isAutoSliding,
        isSpeakerNotes: notes.isSpeakerNotesWindow.bind( notes ),
        isOverview: overview.isActive.bind( overview ),
        isFocused: focus.isFocused.bind( focus ),

        isScrollView: scrollView.isActive.bind( scrollView ),
        isPrintView: printView.isActive.bind( printView ),

        // Checks if reveal.js has been loaded and is ready for use
        isReady: () => ready,

        // Slide preloading
        loadSlide: slideContent.load.bind( slideContent ),
        unloadSlide: slideContent.unload.bind( slideContent ),

        // Start/stop all media inside of the current slide
        startEmbeddedContent: () => slideContent.startEmbeddedContent( currentSlide ),
        stopEmbeddedContent: () => slideContent.stopEmbeddedContent( currentSlide, { unloadIframes: false } ),

        // Preview management
        showPreview,
        hidePreview: closeOverlay,

        // Adds or removes all internal event listeners
        addEventListeners,
        removeEventListeners,
        dispatchEvent,

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

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

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

        // Returns an Array of key:value maps of the attributes of each
        // slide in the deck
        getSlidesAttributes,

        // Returns the number of slides that we have passed
        getSlidePastCount,

        // Returns the total number of slides
        getTotalSlides,

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

        // Returns the previous slide element, may be null
        getPreviousSlide: () => previousSlide,

        // Returns the current slide element
        getCurrentSlide: () => currentSlide,

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

        // Returns the speaker notes string for a slide, or null
        getSlideNotes: notes.getSlideNotes.bind( notes ),

        // Returns an Array of all slides
        getSlides,

        // Returns an array with all horizontal/vertical slides in the deck
        getHorizontalSlides,
        getVerticalSlides,

        // Checks if the presentation contains two or more horizontal
        // and vertical slides
        hasHorizontalSlides,
        hasVerticalSlides,

        // Checks if the deck has navigated on either axis at least once
        hasNavigatedHorizontally: () => navigationHistory.hasNavigatedHorizontally,
        hasNavigatedVertically: () => navigationHistory.hasNavigatedVertically,

        shouldAutoAnimateBetween,

        // Adds/removes a custom key binding
        addKeyBinding: keyboard.addKeyBinding.bind( keyboard ),
        removeKeyBinding: keyboard.removeKeyBinding.bind( keyboard ),

        // Programmatically triggers a keyboard event
        triggerKey: keyboard.triggerKey.bind( keyboard ),

        // Registers a new shortcut to include in the help overlay
        registerKeyboardShortcut: keyboard.registerKeyboardShortcut.bind( keyboard ),

        getComputedSlideSize,
        setCurrentScrollPage,

        // Returns the current scale of the presentation content
        getScale: () => scale,

        // Returns the current configuration object
        getConfig: () => config,

        // Helper method, retrieves query string as a key:value map
        getQueryHash: Util.getQueryHash,

        // Returns the path to the current slide as represented in the URL
        getSlidePath: location.getHash.bind( location ),

        // Returns reveal.js DOM elements
        getRevealElement: () => revealElement,
        getSlidesElement: () => dom.slides,
        getViewportElement: () => dom.viewport,
        getBackgroundsElement: () => backgrounds.element,

        // API for registering and retrieving plugins
        registerPlugin: plugins.registerPlugin.bind( plugins ),
        hasPlugin: plugins.hasPlugin.bind( plugins ),
        getPlugin: plugins.getPlugin.bind( plugins ),
        getPlugins: plugins.getRegisteredPlugins.bind( plugins )

    };

    // Our internal API which controllers have access to
    Util.extend( Reveal, {
        ...API,

        // Methods for announcing content to screen readers
        announceStatus,
        getStatusText,

        // Controllers
        focus,
        scroll: scrollView,
        progress,
        controls,
        location,
        overview,
        fragments,
        backgrounds,
        slideContent,
        slideNumber,

        onUserInput,
        closeOverlay,
        updateSlidesVisibility,
        layoutSlideContents,
        transformSlides,
        cueAutoSlide,
        cancelAutoSlide
    } );

    return API;

};