reveal.js

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

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

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

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

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

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

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

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

		layout();

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

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

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

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

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

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

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

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

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

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

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

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

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

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

		// Update the URL hash
		writeURL();

		cueAutoSlide();

	}

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

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

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

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

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

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

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

		sortAllFragments();

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

		formatEmbeddedContent();

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

	}

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

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

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

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

			} );

		} );

	}

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

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

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

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

			} );

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

		} );

	}

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

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

		var printMode = isPrintingPDF();

		if( slidesLength ) {

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

		return index;

	}

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

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

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

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

			// Limit view distance on weaker devices
			if( isMobileDevice ) {
				viewDistance = isOverview() ? 6 : 2;
			}

			// Limit view distance on weaker devices
			if( isPrintingPDF() ) {
				viewDistance = Number.MAX_VALUE;
			}

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

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

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

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

				if( verticalSlidesLength ) {

					var oy = getPreviousVerticalIndex( horizontalSlide );

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

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

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

				}
			}

		}

	}

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

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

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

		}

	}

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

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

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

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

			var totalSlides = getTotalSlides();

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

	}

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

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

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

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

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

		// Highlight fragment directions
		if( currentSlide ) {

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

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

		}

	}

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

		var currentBackground = null;

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

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

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

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

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

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

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

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

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

				} );
			}

		} );

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

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

		}

		if( currentBackground ) {

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

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

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

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

			previousBackground = currentBackground;

		}

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

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

	}

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

		if( config.parallaxBackgroundImage ) {

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

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

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

			var slideWidth = dom.background.offsetWidth;
			var horizontalSlideCount = horizontalSlides.length;
			var horizontalOffset = -( backgroundWidth - slideWidth ) / ( horizontalSlideCount-1 ) * indexh;

			var slideHeight = dom.background.offsetHeight;
			var verticalSlideCount = verticalSlides.length;
			var verticalOffset = verticalSlideCount > 1 ? -( backgroundHeight - slideHeight ) / ( verticalSlideCount-1 ) * indexv : 0;

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

		}

	}

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

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

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

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

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

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


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

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

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

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

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

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

					background.appendChild( iframe );
				}
			}
		}

	}

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

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

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

	}

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

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

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

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

		return routes;

	}

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

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

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

	}

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

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

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

	}

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

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

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

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

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

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

	}

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

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

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

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

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

	}

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

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

		// The number of past and total slides
		var totalCount = getTotalSlides();
		var pastCount = 0;

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

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

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

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

				pastCount++;

			}

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

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

		}

		if( currentSlide ) {

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

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

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

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

		}

		return pastCount / ( totalCount - 1 );

	}

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

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

	}

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

		var hash = window.location.hash;

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

		// If the first bit is invalid and there is a name we can
		// assume that this is a named link
		if( isNaN( parseInt( bits[0], 10 ) ) && name.length ) {
			var element;

			// Ensure the named link is a valid HTML ID attribute