reveal.js

			if( typeof delay === 'number' ) {
				writeURLTimeout = setTimeout( writeURL, delay );
			}
			else if( currentSlide ) {
				var url = '/';

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

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

				window.location.hash = url;
			}
		}

	}

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

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

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

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

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

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

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

		if( !slide && currentSlide ) {
			var hasFragments = currentSlide.querySelectorAll( '.fragment' ).length > 0;
			if( hasFragments ) {
				var currentFragment = currentSlide.querySelector( '.current-fragment' );
				if( currentFragment && currentFragment.hasAttribute( 'data-fragment-index' ) ) {
					f = parseInt( currentFragment.getAttribute( 'data-fragment-index' ), 10 );
				}
				else {
					f = currentSlide.querySelectorAll( '.fragment.visible' ).length - 1;
				}
			}
		}

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

	}

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

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

	}

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

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

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

		return horizontalSlide;

	}

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

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

			return undefined;
		}

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

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

		return horizontalBackground;

	}

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

		var indices = getIndices();

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

	}

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

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

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

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

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

	}

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

		fragments = toArray( fragments );

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

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

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

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

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

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

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

			index ++;
		} );

		return sorted;

	}

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

		if( currentSlide && config.fragments ) {

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

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

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

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

				var fragmentsShown = [],
					fragmentsHidden = [];

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

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

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

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

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


				} );

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

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

				updateControls();
				updateProgress();

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

			}

		}

		return false;

	}

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

		return navigateFragment( null, 1 );

	}

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

		return navigateFragment( null, -1 );

	}

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

		cancelAutoSlide();

		if( currentSlide ) {

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

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

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

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

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

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

		}

	}

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

		clearTimeout( autoSlideTimeout );
		autoSlideTimeout = -1;

	}

	function pauseAutoSlide() {

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

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

	}

	function resumeAutoSlide() {

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

	}

	function navigateLeft() {

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

	}

	function navigateRight() {

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

	}

	function navigateUp() {

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

	}

	function navigateDown() {

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

	}

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

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

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

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

	}

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

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

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

	}


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

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

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

	}

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

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

	}

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

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

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

		onUserInput( event );

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

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

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

		var triggered = false;

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

			for( var key in config.keyboard ) {

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

					var value = config.keyboard[ key ];

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

					triggered = true;

				}

			}

		}

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

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

			switch( event.keyCode ) {
				// p, page up
				case 80: case 33: navigatePrev(); break;
				// n, page down
				case 78: case 34: navigateNext(); break;
				// h, left
				case 72: case 37: navigateLeft(); break;
				// l, right
				case 76: case 39: navigateRight(); break;
				// k, up
				case 75: case 38: navigateUp(); break;
				// j, down
				case 74: case 40: navigateDown(); break;
				// home
				case 36: slide( 0 ); break;
				// end
				case 35: slide( Number.MAX_VALUE ); break;
				// space
				case 32: isOverview() ? deactivateOverview() : event.shiftKey ? navigatePrev() : navigateNext(); break;
				// return
				case 13: isOverview() ? deactivateOverview() : triggered = false; break;
				// two-spot, semicolon, b, period, Logitech presenter tools "black screen" button
				case 58: case 59: case 66: case 190: case 191: togglePause(); break;
				// f
				case 70: enterFullscreen(); break;
				// a
				case 65: if ( config.autoSlideStoppable ) toggleAutoSlide( autoSlideWasPaused ); break;
				default:
					triggered = false;
			}

		}

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

			event.preventDefault && event.preventDefault();
		}

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

	}

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

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

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

	}

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

		// Each touch should only trigger one action
		if( !touch.captured ) {
			onUserInput( event );

			var currentX = event.touches[0].clientX;
			var currentY = event.touches[0].clientY;

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

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

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

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

				event.preventDefault();

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

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

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

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

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

	}

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

		touch.captured = false;

	}

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

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

	}

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

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

	}

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

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

	}

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

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

			lastMouseWheelStep = Date.now();

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

		}

	}

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

		onUserInput( event );

		event.preventDefault();

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

		slide( slideIndex );

	}

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

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

		readURL();

	}

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

		layout();

	}

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

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

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

	}

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

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

			var element = event.target;

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

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

				deactivateOverview();

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

					slide( h, v );
				}

			}
		}

	}

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

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