]> scripts.mit.edu Git - autoinstalls/wordpress.git/blobdiff - wp-admin/js/customize-controls.js
Wordpress 4.6-scripts
[autoinstalls/wordpress.git] / wp-admin / js / customize-controls.js
index f43630a14a9ee6d243ba05d3e7444e2476e3fbe7..8fa7bb09ee2cc8960a70e3e8000e4bcbd9a3893a 100644 (file)
@@ -1,15 +1,24 @@
-/* globals _wpCustomizeHeader, _wpCustomizeBackground, _wpMediaViewsL10n */
+/* global _wpCustomizeHeader, _wpCustomizeBackground, _wpMediaViewsL10n, MediaElementPlayer */
 (function( exports, $ ){
        var Container, focus, api = wp.customize;
 
        /**
+        * A Customizer Setting.
+        *
+        * A setting is WordPress data (theme mod, option, menu, etc.) that the user can
+        * draft changes to in the Customizer.
+        *
+        * @see PHP class WP_Customize_Setting.
+        *
         * @class
         * @augments wp.customize.Value
         * @augments wp.customize.Class
         *
-        * @param options
-        * - previewer - The Previewer instance to sync with.
-        * - transport - The transport to use for previewing. Supports 'refresh' and 'postMessage'.
+        * @param {object} id                The Setting ID.
+        * @param {object} value             The initial value of the setting.
+        * @param {object} options.previewer The Previewer instance to sync with.
+        * @param {object} options.transport The transport to use for previewing. Supports 'refresh' and 'postMessage'.
+        * @param {object} options.dirty
         */
        api.Setting = api.Value.extend({
                initialize: function( id, value, options ) {
 
                        this.id = id;
                        this.transport = this.transport || 'refresh';
+                       this._dirty = options.dirty || false;
+                       this.notifications = new api.Values({ defaultConstructor: api.Notification });
 
+                       // Whenever the setting's value changes, refresh the preview.
                        this.bind( this.preview );
                },
+
+               /**
+                * Refresh the preview, respective of the setting's refresh policy.
+                */
                preview: function() {
                        switch ( this.transport ) {
                                case 'refresh':
                                case 'postMessage':
                                        return this.previewer.send( 'setting', [ this.id, this() ] );
                        }
+               },
+
+               /**
+                * Find controls associated with this setting.
+                *
+                * @since 4.6.0
+                * @returns {wp.customize.Control[]} Controls associated with setting.
+                */
+               findControls: function() {
+                       var setting = this, controls = [];
+                       api.control.each( function( control ) {
+                               _.each( control.settings, function( controlSetting ) {
+                                       if ( controlSetting.id === setting.id ) {
+                                               controls.push( control );
+                                       }
+                               } );
+                       } );
+                       return controls;
                }
        });
 
         * @since 4.1.0
         *
         * @param {Object}   [params]
-        * @param {Callback} [params.completeCallback]
+        * @param {Function} [params.completeCallback]
         */
        focus = function ( params ) {
-               var construct, completeCallback, focus;
+               var construct, completeCallback, focus, focusElement;
                construct = this;
                params = params || {};
                focus = function () {
-                       construct.container.find( ':focusable:first' ).focus();
-                       construct.container[0].scrollIntoView( true );
+                       var focusContainer;
+                       if ( construct.extended( api.Panel ) && construct.expanded && construct.expanded() ) {
+                               focusContainer = construct.container.find( 'ul.control-panel-content' );
+                       } else if ( construct.extended( api.Section ) && construct.expanded && construct.expanded() ) {
+                               focusContainer = construct.container.find( 'ul.accordion-section-content' );
+                       } else {
+                               focusContainer = construct.container;
+                       }
+
+                       focusElement = focusContainer.find( '.control-focus:first' );
+                       if ( 0 === focusElement.length ) {
+                               // Note that we can't use :focusable due to a jQuery UI issue. See: https://github.com/jquery/jquery-ui/pull/1583
+                               focusElement = focusContainer.find( 'input, select, textarea, button, object, a[href], [tabindex]' ).filter( ':visible' ).first();
+                       }
+                       focusElement.focus();
                };
                if ( params.completeCallback ) {
                        completeCallback = params.completeCallback;
        Container = api.Class.extend({
                defaultActiveArguments: { duration: 'fast', completeCallback: $.noop },
                defaultExpandedArguments: { duration: 'fast', completeCallback: $.noop },
+               containerType: 'container',
+               defaults: {
+                       title: '',
+                       description: '',
+                       priority: 100,
+                       type: 'default',
+                       content: null,
+                       active: true,
+                       instanceNumber: null
+               },
 
                /**
                 * @since 4.1.0
                 *
-                * @param {String} id
-                * @param {Object} options
+                * @param {string}         id - The ID for the container.
+                * @param {object}         options - Object containing one property: params.
+                * @param {object}         options.params - Object containing the following properties.
+                * @param {string}         options.params.title - Title shown when panel is collapsed and expanded.
+                * @param {string=}        [options.params.description] - Description shown at the top of the panel.
+                * @param {number=100}     [options.params.priority] - The sort priority for the panel.
+                * @param {string=default} [options.params.type] - The type of the panel. See wp.customize.panelConstructor.
+                * @param {string=}        [options.params.content] - The markup to be used for the panel container. If empty, a JS template is used.
+                * @param {boolean=true}   [options.params.active] - Whether the panel is active or not.
                 */
                initialize: function ( id, options ) {
                        var container = this;
                        container.id = id;
-                       container.params = {};
-                       $.extend( container, options || {} );
+                       options = options || {};
+
+                       options.params = _.defaults(
+                               options.params || {},
+                               container.defaults
+                       );
+
+                       $.extend( container, options );
+                       container.templateSelector = 'customize-' + container.containerType + '-' + container.params.type;
                        container.container = $( container.params.content );
+                       if ( 0 === container.container.length ) {
+                               container.container = $( container.getContainer() );
+                       }
 
                        container.deferred = {
                                embedded: new $.Deferred()
                                container.onChangeExpanded( expanded, args );
                        });
 
-                       container.attachEvents();
+                       container.deferred.embedded.done( function () {
+                               container.attachEvents();
+                       });
 
                        api.utils.bubbleChildValueChanges( container, [ 'priority', 'active' ] );
 
-                       container.priority.set( isNaN( container.params.priority ) ? 100 : container.params.priority );
+                       container.priority.set( container.params.priority );
                        container.active.set( container.params.active );
                        container.expanded.set( false );
                },
                },
 
                /**
-                * Handle changes to the active state.
+                * Active state change handler.
                 *
-                * This does not change the active state, it merely handles the behavior
-                * for when it does change.
+                * Shows the container if it is active, hides it if not.
                 *
                 * To override by subclass, update the container's UI to reflect the provided active state.
                 *
                 * @param {Object}  args.duration
                 * @param {Object}  args.completeCallback
                 */
-               onChangeActive: function ( active, args ) {
-                       var duration = ( 'resolved' === api.previewer.deferred.active.state() ? args.duration : 0 );
-                       if ( ! $.contains( document, this.container ) ) {
+               onChangeActive: function( active, args ) {
+                       var duration, construct = this, expandedOtherPanel;
+                       if ( args.unchanged ) {
+                               if ( args.completeCallback ) {
+                                       args.completeCallback();
+                               }
+                               return;
+                       }
+
+                       duration = ( 'resolved' === api.previewer.deferred.active.state() ? args.duration : 0 );
+
+                       if ( construct.extended( api.Panel ) ) {
+                               // If this is a panel is not currently expanded but another panel is expanded, do not animate.
+                               api.panel.each(function ( panel ) {
+                                       if ( panel !== construct && panel.expanded() ) {
+                                               expandedOtherPanel = panel;
+                                               duration = 0;
+                                       }
+                               });
+
+                               // Collapse any expanded sections inside of this panel first before deactivating.
+                               if ( ! active ) {
+                                       _.each( construct.sections(), function( section ) {
+                                               section.collapse( { duration: 0 } );
+                                       } );
+                               }
+                       }
+
+                       if ( ! $.contains( document, construct.container[0] ) ) {
                                // jQuery.fn.slideUp is not hiding an element if it is not in the DOM
-                               this.container.toggle( active );
+                               construct.container.toggle( active );
                                if ( args.completeCallback ) {
                                        args.completeCallback();
                                }
                        } else if ( active ) {
-                               this.container.stop( true, true ).slideDown( duration, args.completeCallback );
+                               construct.container.stop( true, true ).slideDown( duration, args.completeCallback );
                        } else {
-                               this.container.stop( true, true ).slideUp( duration, args.completeCallback );
+                               if ( construct.expanded() ) {
+                                       construct.collapse({
+                                               duration: duration,
+                                               completeCallback: function() {
+                                                       construct.container.stop( true, true ).slideUp( duration, args.completeCallback );
+                                               }
+                                       });
+                               } else {
+                                       construct.container.stop( true, true ).slideUp( duration, args.completeCallback );
+                               }
+                       }
+
+                       // Recalculate the margin-top immediately, not waiting for debounced reflow, to prevent momentary (100ms) vertical jiggle.
+                       if ( expandedOtherPanel ) {
+                               expandedOtherPanel._recalculateTopMargin();
                        }
                },
 
                },
 
                /**
-                * @param {Boolean} expanded
-                * @param {Object} [params]
-                * @returns {Boolean} false if state already applied
+                * Handle the toggle logic for expand/collapse.
+                *
+                * @param {Boolean}  expanded - The new state to apply.
+                * @param {Object}   [params] - Object containing options for expand/collapse.
+                * @param {Function} [params.completeCallback] - Function to call when expansion/collapse is complete.
+                * @returns {Boolean} false if state already applied or active state is false
                 */
-               _toggleExpanded: function ( expanded, params ) {
-                       var self = this;
+               _toggleExpanded: function( expanded, params ) {
+                       var instance = this, previousCompleteCallback;
                        params = params || {};
-                       if ( ( expanded && this.expanded.get() ) || ( ! expanded && ! this.expanded.get() ) ) {
+                       previousCompleteCallback = params.completeCallback;
+
+                       // Short-circuit expand() if the instance is not active.
+                       if ( expanded && ! instance.active() ) {
+                               return false;
+                       }
+
+                       params.completeCallback = function() {
+                               if ( previousCompleteCallback ) {
+                                       previousCompleteCallback.apply( instance, arguments );
+                               }
+                               if ( expanded ) {
+                                       instance.container.trigger( 'expanded' );
+                               } else {
+                                       instance.container.trigger( 'collapsed' );
+                               }
+                       };
+                       if ( ( expanded && instance.expanded.get() ) || ( ! expanded && ! instance.expanded.get() ) ) {
                                params.unchanged = true;
-                               self.onChangeExpanded( self.expanded.get(), params );
+                               instance.onChangeExpanded( instance.expanded.get(), params );
                                return false;
                        } else {
                                params.unchanged = false;
-                               this.expandedArgumentsQueue.push( params );
-                               this.expanded.set( expanded );
+                               instance.expandedArgumentsQueue.push( params );
+                               instance.expanded.set( expanded );
                                return true;
                        }
                },
 
                /**
                 * @param {Object} [params]
-                * @returns {Boolean} false if already expanded
+                * @returns {Boolean} false if already expanded or if inactive.
                 */
                expand: function ( params ) {
                        return this._toggleExpanded( true, params );
 
                /**
                 * @param {Object} [params]
-                * @returns {Boolean} false if already collapsed
+                * @returns {Boolean} false if already collapsed.
                 */
                collapse: function ( params ) {
                        return this._toggleExpanded( false, params );
                 * Bring the container into view and then expand this and bring it into view
                 * @param {Object} [params]
                 */
-               focus: focus
+               focus: focus,
+
+               /**
+                * Return the container html, generated from its JS template, if it exists.
+                *
+                * @since 4.3.0
+                */
+               getContainer: function () {
+                       var template,
+                               container = this;
+
+                       if ( 0 !== $( '#tmpl-' + container.templateSelector ).length ) {
+                               template = wp.template( container.templateSelector );
+                       } else {
+                               template = wp.template( 'customize-' + container.containerType + '-default' );
+                       }
+                       if ( template && container.container ) {
+                               return $.trim( template( container.params ) );
+                       }
+
+                       return '<li></li>';
+               }
        });
 
        /**
         * @augments wp.customize.Class
         */
        api.Section = Container.extend({
+               containerType: 'section',
+               defaults: {
+                       title: '',
+                       description: '',
+                       priority: 100,
+                       type: 'default',
+                       content: null,
+                       active: true,
+                       instanceNumber: null,
+                       panel: null,
+                       customizeAction: ''
+               },
 
                /**
                 * @since 4.1.0
                 *
-                * @param {String} id
-                * @param {Array}  options
+                * @param {string}         id - The ID for the section.
+                * @param {object}         options - Object containing one property: params.
+                * @param {object}         options.params - Object containing the following properties.
+                * @param {string}         options.params.title - Title shown when section is collapsed and expanded.
+                * @param {string=}        [options.params.description] - Description shown at the top of the section.
+                * @param {number=100}     [options.params.priority] - The sort priority for the section.
+                * @param {string=default} [options.params.type] - The type of the section. See wp.customize.sectionConstructor.
+                * @param {string=}        [options.params.content] - The markup to be used for the section container. If empty, a JS template is used.
+                * @param {boolean=true}   [options.params.active] - Whether the section is active or not.
+                * @param {string}         options.params.panel - The ID for the panel this section is associated with.
+                * @param {string=}        [options.params.customizeAction] - Additional context information shown before the section title when expanded.
                 */
                initialize: function ( id, options ) {
                        var section = this;
                        };
                        section.panel.bind( inject );
                        inject( section.panel.get() ); // Since a section may never get a panel, assume that it won't ever get one
+
+                       section.deferred.embedded.done(function() {
+                               // Fix the top margin after reflow.
+                               api.bind( 'pane-contents-reflowed', _.debounce( function() {
+                                       section._recalculateTopMargin();
+                               }, 100 ) );
+                       });
                },
 
                /**
                        var section = this;
 
                        // Expand/Collapse accordion sections on click.
-                       section.container.find( '.accordion-section-title' ).on( 'click keydown', function( event ) {
+                       section.container.find( '.accordion-section-title, .customize-section-back' ).on( 'click keydown', function( event ) {
                                if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
                                        return;
                                }
                 */
                onChangeExpanded: function ( expanded, args ) {
                        var section = this,
+                               container = section.container.closest( '.wp-full-overlay-sidebar-content' ),
                                content = section.container.find( '.accordion-section-content' ),
-                               expand;
+                               overlay = section.container.closest( '.wp-full-overlay' ),
+                               backBtn = section.container.find( '.customize-section-back' ),
+                               sectionTitle = section.container.find( '.accordion-section-title' ).first(),
+                               headerActionsHeight = $( '#customize-header-actions' ).height(),
+                               resizeContentHeight, expand, position, scroll;
 
-                       if ( expanded ) {
+                       if ( expanded && ! section.container.hasClass( 'open' ) ) {
 
                                if ( args.unchanged ) {
                                        expand = args.completeCallback;
                                } else {
-                                       expand = function () {
-                                               content.stop().slideDown( args.duration, args.completeCallback );
+                                       container.scrollTop( 0 );
+                                       resizeContentHeight = function() {
+                                               var matchMedia, offset;
+                                               matchMedia = window.matchMedia || window.msMatchMedia;
+                                               offset = 90; // 45px for customize header actions + 45px for footer actions.
+
+                                               // No footer on small screens.
+                                               if ( matchMedia && matchMedia( '(max-width: 640px)' ).matches ) {
+                                                       offset = 45;
+                                               }
+                                               content.css( 'height', ( window.innerHeight - offset ) );
+                                       };
+                                       expand = function() {
                                                section.container.addClass( 'open' );
+                                               overlay.addClass( 'section-open' );
+                                               position = content.offset().top;
+                                               scroll = container.scrollTop();
+                                               content.css( 'margin-top', ( headerActionsHeight - position - scroll ) );
+                                               resizeContentHeight();
+                                               sectionTitle.attr( 'tabindex', '-1' );
+                                               backBtn.attr( 'tabindex', '0' );
+                                               backBtn.focus();
+                                               if ( args.completeCallback ) {
+                                                       args.completeCallback();
+                                               }
+
+                                               // Fix the height after browser resize.
+                                               $( window ).on( 'resize.customizer-section', _.debounce( resizeContentHeight, 100 ) );
+
+                                               setTimeout( _.bind( section._recalculateTopMargin, section ), 0 );
                                        };
                                }
 
                                                completeCallback: expand
                                        });
                                } else {
+                                       api.panel.each( function( panel ) {
+                                               panel.collapse();
+                                       });
                                        expand();
                                }
 
-                       } else {
+                       } else if ( ! expanded && section.container.hasClass( 'open' ) ) {
                                section.container.removeClass( 'open' );
-                               content.slideUp( args.duration, args.completeCallback );
+                               overlay.removeClass( 'section-open' );
+                               content.css( 'margin-top', '' );
+                               container.scrollTop( 0 );
+                               backBtn.attr( 'tabindex', '-1' );
+                               sectionTitle.attr( 'tabindex', '0' );
+                               sectionTitle.focus();
+                               if ( args.completeCallback ) {
+                                       args.completeCallback();
+                               }
+                               $( window ).off( 'resize.customizer-section' );
+                       } else {
+                               if ( args.completeCallback ) {
+                                       args.completeCallback();
+                               }
+                       }
+               },
+
+               /**
+                * Recalculate the top margin.
+                *
+                * @since 4.4.0
+                * @private
+                */
+               _recalculateTopMargin: function() {
+                       var section = this, content, offset, headerActionsHeight;
+                       content = section.container.find( '.accordion-section-content' );
+                       if ( 0 === content.length ) {
+                               return;
+                       }
+                       headerActionsHeight = $( '#customize-header-actions' ).height();
+                       offset = ( content.offset().top - headerActionsHeight );
+                       if ( 0 < offset ) {
+                               content.css( 'margin-top', ( parseInt( content.css( 'margin-top' ), 10 ) - offset ) );
                        }
                }
        });
 
        /**
-        * @since 4.1.0
+        * wp.customize.ThemesSection
         *
-        * @class
-        * @augments wp.customize.Class
+        * Custom section for themes that functions similarly to a backwards panel,
+        * and also handles the theme-details view rendering and navigation.
+        *
+        * @constructor
+        * @augments wp.customize.Section
+        * @augments wp.customize.Container
         */
-       api.Panel = Container.extend({
+       api.ThemesSection = api.Section.extend({
+               currentTheme: '',
+               overlay: '',
+               template: '',
+               screenshotQueue: null,
+               $window: $( window ),
+
                /**
-                * @since 4.1.0
-                *
-                * @param  {String} id
-                * @param  {Object} options
+                * @since 4.2.0
                 */
-               initialize: function ( id, options ) {
-                       var panel = this;
-                       Container.prototype.initialize.call( panel, id, options );
-                       panel.embed();
-                       panel.deferred.embedded.done( function () {
-                               panel.ready();
+               initialize: function () {
+                       this.$customizeSidebar = $( '.wp-full-overlay-sidebar-content:first' );
+                       return api.Section.prototype.initialize.apply( this, arguments );
+               },
+
+               /**
+                * @since 4.2.0
+                */
+               ready: function () {
+                       var section = this;
+                       section.overlay = section.container.find( '.theme-overlay' );
+                       section.template = wp.template( 'customize-themes-details-view' );
+
+                       // Bind global keyboard events.
+                       $( 'body' ).on( 'keyup', function( event ) {
+                               if ( ! section.overlay.find( '.theme-wrap' ).is( ':visible' ) ) {
+                                       return;
+                               }
+
+                               // Pressing the right arrow key fires a theme:next event
+                               if ( 39 === event.keyCode ) {
+                                       section.nextTheme();
+                               }
+
+                               // Pressing the left arrow key fires a theme:previous event
+                               if ( 37 === event.keyCode ) {
+                                       section.previousTheme();
+                               }
+
+                               // Pressing the escape key fires a theme:collapse event
+                               if ( 27 === event.keyCode ) {
+                                       section.closeDetails();
+                               }
                        });
+
+                       _.bindAll( this, 'renderScreenshots' );
                },
 
                /**
-                * Embed the container in the DOM when any parent panel is ready.
+                * Override Section.isContextuallyActive method.
                 *
-                * @since 4.1.0
+                * Ignore the active states' of the contained theme controls, and just
+                * use the section's own active state instead. This ensures empty search
+                * results for themes to cause the section to become inactive.
+                *
+                * @since 4.2.0
+                *
+                * @returns {Boolean}
                 */
-               embed: function () {
-                       var panel = this,
-                               parentContainer = $( '#customize-theme-controls > ul' ); // @todo This should be defined elsewhere, and to be configurable
-
-                       if ( ! panel.container.parent().is( parentContainer ) ) {
-                               parentContainer.append( panel.container );
-                       }
-                       panel.deferred.embedded.resolve();
+               isContextuallyActive: function () {
+                       return this.active();
                },
 
                /**
-                * @since 4.1.0
+                * @since 4.2.0
                 */
                attachEvents: function () {
-                       var meta, panel = this;
+                       var section = this;
 
-                       // Expand/Collapse accordion sections on click.
-                       panel.container.find( '.accordion-section-title' ).on( 'click keydown', function( event ) {
+                       // Expand/Collapse section/panel.
+                       section.container.find( '.change-theme, .customize-theme' ).on( 'click keydown', function( event ) {
                                if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
                                        return;
                                }
                                event.preventDefault(); // Keep this AFTER the key filter above
 
-                               if ( ! panel.expanded() ) {
-                                       panel.expand();
+                               if ( section.expanded() ) {
+                                       section.collapse();
+                               } else {
+                                       section.expand();
                                }
                        });
 
-                       meta = panel.container.find( '.panel-meta:first' );
-
-                       meta.find( '> .accordion-section-title' ).on( 'click keydown', function( event ) {
+                       // Theme navigation in details view.
+                       section.container.on( 'click keydown', '.left', function( event ) {
                                if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
                                        return;
                                }
+
                                event.preventDefault(); // Keep this AFTER the key filter above
 
-                               if ( meta.hasClass( 'cannot-expand' ) ) {
+                               section.previousTheme();
+                       });
+
+                       section.container.on( 'click keydown', '.right', function( event ) {
+                               if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
                                        return;
                                }
 
-                               var content = meta.find( '.accordion-section-content:first' );
-                               if ( meta.hasClass( 'open' ) ) {
-                                       meta.toggleClass( 'open' );
-                                       content.slideUp( panel.defaultExpandedArguments.duration );
-                               } else {
-                                       content.slideDown( panel.defaultExpandedArguments.duration );
-                                       meta.toggleClass( 'open' );
+                               event.preventDefault(); // Keep this AFTER the key filter above
+
+                               section.nextTheme();
+                       });
+
+                       section.container.on( 'click keydown', '.theme-backdrop, .close', function( event ) {
+                               if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                                       return;
                                }
+
+                               event.preventDefault(); // Keep this AFTER the key filter above
+
+                               section.closeDetails();
                        });
 
-               },
+                       var renderScreenshots = _.throttle( _.bind( section.renderScreenshots, this ), 100 );
+                       section.container.on( 'input', '#themes-filter', function( event ) {
+                               var count,
+                                       term = event.currentTarget.value.toLowerCase().trim().replace( '-', ' ' ),
+                                       controls = section.controls();
 
-               /**
-                * Get the sections that are associated with this panel, sorted by their priority Value.
-                *
-                * @since 4.1.0
-                *
-                * @returns {Array}
-                */
-               sections: function () {
-                       return this._children( 'panel', 'section' );
-               },
+                               _.each( controls, function( control ) {
+                                       control.filter( term );
+                               });
 
-               /**
-                * Return whether this panel has any active sections.
-                *
-                * @since 4.1.0
-                *
-                * @returns {boolean}
-                */
-               isContextuallyActive: function () {
-                       var panel = this,
-                               sections = panel.sections(),
-                               activeCount = 0;
-                       _( sections ).each( function ( section ) {
-                               if ( section.active() && section.isContextuallyActive() ) {
-                                       activeCount += 1;
-                               }
-                       );
-                       return ( activeCount !== 0 );
+                               renderScreenshots();
+
+                               // Update theme count.
+                               count = section.container.find( 'li.customize-control:visible' ).length;
+                               section.container.find( '.theme-count' ).text( count );
+                       });
+
+                       // Pre-load the first 3 theme screenshots.
+                       api.bind( 'ready', function () {
+                               _.each( section.controls().slice( 0, 3 ), function ( control ) {
+                                       var img, src = control.params.theme.screenshot[0];
+                                       if ( src ) {
+                                               img = new Image();
+                                               img.src = src;
+                                       }
+                               });
+                       });
                },
 
                /**
                 * Update UI to reflect expanded state
                 *
-                * @since 4.1.0
+                * @since 4.2.0
                 *
                 * @param {Boolean}  expanded
                 * @param {Object}   args
                                panel = this,
                                section = panel.container.closest( '.accordion-section' ),
                                overlay = section.closest( '.wp-full-overlay' ),
-                               container = section.closest( '.accordion-container' ),
+                               container = section.closest( '.wp-full-overlay-sidebar-content' ),
                                siblings = container.find( '.open' ),
-                               topPanel = overlay.find( '#customize-theme-controls > ul > .accordion-section > .accordion-section-title' ).add( '#customize-info > .accordion-section-title' ),
-                               backBtn = overlay.find( '.control-panel-back' ),
-                               panelTitle = section.find( '.accordion-section-title' ).first(),
+                               customizeBtn = section.find( '.customize-theme' ),
+                               changeBtn = section.find( '.change-theme' ),
                                content = section.find( '.control-panel-content' );
 
                        if ( expanded ) {
 
                                // Collapse any sibling sections/panels
-                               api.section.each( function ( section ) {
-                                       if ( ! section.panel() ) {
-                                               section.collapse( { duration: 0 } );
+                               api.section.each( function ( otherSection ) {
+                                       if ( otherSection !== panel ) {
+                                               otherSection.collapse( { duration: args.duration } );
                                        }
                                });
                                api.panel.each( function ( otherPanel ) {
-                                       if ( panel !== otherPanel ) {
-                                               otherPanel.collapse( { duration: 0 } );
-                                       }
+                                       otherPanel.collapse( { duration: 0 } );
                                });
 
                                content.show( 0, function() {
                                        position = content.offset().top;
                                        scroll = container.scrollTop();
-                                       content.css( 'margin-top', ( 45 - position - scroll ) );
+                                       content.css( 'margin-top', ( $( '#customize-header-actions' ).height() - position - scroll ) );
                                        section.addClass( 'current-panel' );
-                                       overlay.addClass( 'in-sub-panel' );
+                                       overlay.addClass( 'in-themes-panel' );
                                        container.scrollTop( 0 );
+                                       _.delay( panel.renderScreenshots, 10 ); // Wait for the controls
+                                       panel.$customizeSidebar.on( 'scroll.customize-themes-section', _.throttle( panel.renderScreenshots, 300 ) );
                                        if ( args.completeCallback ) {
                                                args.completeCallback();
                                        }
                                } );
-                               topPanel.attr( 'tabindex', '-1' );
-                               backBtn.attr( 'tabindex', '0' );
-                               backBtn.focus();
+                               customizeBtn.focus();
                        } else {
                                siblings.removeClass( 'open' );
                                section.removeClass( 'current-panel' );
-                               overlay.removeClass( 'in-sub-panel' );
+                               overlay.removeClass( 'in-themes-panel' );
+                               panel.$customizeSidebar.off( 'scroll.customize-themes-section' );
                                content.delay( 180 ).hide( 0, function() {
                                        content.css( 'margin-top', 'inherit' ); // Reset
                                        if ( args.completeCallback ) {
                                                args.completeCallback();
                                        }
                                } );
-                               topPanel.attr( 'tabindex', '0' );
-                               backBtn.attr( 'tabindex', '-1' );
-                               panelTitle.focus();
+                               customizeBtn.attr( 'tabindex', '0' );
+                               changeBtn.focus();
                                container.scrollTop( 0 );
                        }
-               }
-       });
+               },
 
-       /**
-        * A Customizer Control.
-        *
-        * A control provides a UI element that allows a user to modify a Customizer Setting.
-        *
-        * @see PHP class WP_Customize_Control.
-        *
-        * @class
-        * @augments wp.customize.Class
-        *
-        * @param {string} id                            Unique identifier for the control instance.
-        * @param {object} options                       Options hash for the control instance.
-        * @param {object} options.params
-        * @param {object} options.params.type           Type of control (e.g. text, radio, dropdown-pages, etc.)
-        * @param {string} options.params.content        The HTML content for the control.
-        * @param {string} options.params.priority       Order of priority to show the control within the section.
-        * @param {string} options.params.active
-        * @param {string} options.params.section
-        * @param {string} options.params.label
-        * @param {string} options.params.description
-        * @param {string} options.params.instanceNumber Order in which this instance was created in relation to other instances.
-        */
-       api.Control = api.Class.extend({
-               defaultActiveArguments: { duration: 'fast', completeCallback: $.noop },
+               /**
+                * Recalculate the top margin.
+                *
+                * @since 4.4.0
+                * @private
+                */
+               _recalculateTopMargin: function() {
+                       api.Panel.prototype._recalculateTopMargin.call( this );
+               },
 
-               initialize: function( id, options ) {
-                       var control = this,
-                               nodes, radios, settings;
+               /**
+                * Render control's screenshot if the control comes into view.
+                *
+                * @since 4.2.0
+                */
+               renderScreenshots: function( ) {
+                       var section = this;
+
+                       // Fill queue initially.
+                       if ( section.screenshotQueue === null ) {
+                               section.screenshotQueue = section.controls();
+                       }
+
+                       // Are all screenshots rendered?
+                       if ( ! section.screenshotQueue.length ) {
+                               return;
+                       }
+
+                       section.screenshotQueue = _.filter( section.screenshotQueue, function( control ) {
+                               var $imageWrapper = control.container.find( '.theme-screenshot' ),
+                                       $image = $imageWrapper.find( 'img' );
+
+                               if ( ! $image.length ) {
+                                       return false;
+                               }
+
+                               if ( $image.is( ':hidden' ) ) {
+                                       return true;
+                               }
+
+                               // Based on unveil.js.
+                               var wt = section.$window.scrollTop(),
+                                       wb = wt + section.$window.height(),
+                                       et = $image.offset().top,
+                                       ih = $imageWrapper.height(),
+                                       eb = et + ih,
+                                       threshold = ih * 3,
+                                       inView = eb >= wt - threshold && et <= wb + threshold;
+
+                               if ( inView ) {
+                                       control.container.trigger( 'render-screenshot' );
+                               }
+
+                               // If the image is in view return false so it's cleared from the queue.
+                               return ! inView;
+                       } );
+               },
+
+               /**
+                * Advance the modal to the next theme.
+                *
+                * @since 4.2.0
+                */
+               nextTheme: function () {
+                       var section = this;
+                       if ( section.getNextTheme() ) {
+                               section.showDetails( section.getNextTheme(), function() {
+                                       section.overlay.find( '.right' ).focus();
+                               } );
+                       }
+               },
+
+               /**
+                * Get the next theme model.
+                *
+                * @since 4.2.0
+                */
+               getNextTheme: function () {
+                       var control, next;
+                       control = api.control( 'theme_' + this.currentTheme );
+                       next = control.container.next( 'li.customize-control-theme' );
+                       if ( ! next.length ) {
+                               return false;
+                       }
+                       next = next[0].id.replace( 'customize-control-', '' );
+                       control = api.control( next );
+
+                       return control.params.theme;
+               },
+
+               /**
+                * Advance the modal to the previous theme.
+                *
+                * @since 4.2.0
+                */
+               previousTheme: function () {
+                       var section = this;
+                       if ( section.getPreviousTheme() ) {
+                               section.showDetails( section.getPreviousTheme(), function() {
+                                       section.overlay.find( '.left' ).focus();
+                               } );
+                       }
+               },
+
+               /**
+                * Get the previous theme model.
+                *
+                * @since 4.2.0
+                */
+               getPreviousTheme: function () {
+                       var control, previous;
+                       control = api.control( 'theme_' + this.currentTheme );
+                       previous = control.container.prev( 'li.customize-control-theme' );
+                       if ( ! previous.length ) {
+                               return false;
+                       }
+                       previous = previous[0].id.replace( 'customize-control-', '' );
+                       control = api.control( previous );
+
+                       return control.params.theme;
+               },
+
+               /**
+                * Disable buttons when we're viewing the first or last theme.
+                *
+                * @since 4.2.0
+                */
+               updateLimits: function () {
+                       if ( ! this.getNextTheme() ) {
+                               this.overlay.find( '.right' ).addClass( 'disabled' );
+                       }
+                       if ( ! this.getPreviousTheme() ) {
+                               this.overlay.find( '.left' ).addClass( 'disabled' );
+                       }
+               },
+
+               /**
+                * Render & show the theme details for a given theme model.
+                *
+                * @since 4.2.0
+                *
+                * @param {Object}   theme
+                */
+               showDetails: function ( theme, callback ) {
+                       var section = this;
+                       callback = callback || function(){};
+                       section.currentTheme = theme.id;
+                       section.overlay.html( section.template( theme ) )
+                               .fadeIn( 'fast' )
+                               .focus();
+                       $( 'body' ).addClass( 'modal-open' );
+                       section.containFocus( section.overlay );
+                       section.updateLimits();
+                       callback();
+               },
+
+               /**
+                * Close the theme details modal.
+                *
+                * @since 4.2.0
+                */
+               closeDetails: function () {
+                       $( 'body' ).removeClass( 'modal-open' );
+                       this.overlay.fadeOut( 'fast' );
+                       api.control( 'theme_' + this.currentTheme ).focus();
+               },
+
+               /**
+                * Keep tab focus within the theme details modal.
+                *
+                * @since 4.2.0
+                */
+               containFocus: function( el ) {
+                       var tabbables;
+
+                       el.on( 'keydown', function( event ) {
+
+                               // Return if it's not the tab key
+                               // When navigating with prev/next focus is already handled
+                               if ( 9 !== event.keyCode ) {
+                                       return;
+                               }
+
+                               // uses jQuery UI to get the tabbable elements
+                               tabbables = $( ':tabbable', el );
+
+                               // Keep focus within the overlay
+                               if ( tabbables.last()[0] === event.target && ! event.shiftKey ) {
+                                       tabbables.first().focus();
+                                       return false;
+                               } else if ( tabbables.first()[0] === event.target && event.shiftKey ) {
+                                       tabbables.last().focus();
+                                       return false;
+                               }
+                       });
+               }
+       });
+
+       /**
+        * @since 4.1.0
+        *
+        * @class
+        * @augments wp.customize.Class
+        */
+       api.Panel = Container.extend({
+               containerType: 'panel',
+
+               /**
+                * @since 4.1.0
+                *
+                * @param {string}         id - The ID for the panel.
+                * @param {object}         options - Object containing one property: params.
+                * @param {object}         options.params - Object containing the following properties.
+                * @param {string}         options.params.title - Title shown when panel is collapsed and expanded.
+                * @param {string=}        [options.params.description] - Description shown at the top of the panel.
+                * @param {number=100}     [options.params.priority] - The sort priority for the panel.
+                * @param {string=default} [options.params.type] - The type of the panel. See wp.customize.panelConstructor.
+                * @param {string=}        [options.params.content] - The markup to be used for the panel container. If empty, a JS template is used.
+                * @param {boolean=true}   [options.params.active] - Whether the panel is active or not.
+                */
+               initialize: function ( id, options ) {
+                       var panel = this;
+                       Container.prototype.initialize.call( panel, id, options );
+                       panel.embed();
+                       panel.deferred.embedded.done( function () {
+                               panel.ready();
+                       });
+               },
+
+               /**
+                * Embed the container in the DOM when any parent panel is ready.
+                *
+                * @since 4.1.0
+                */
+               embed: function () {
+                       var panel = this,
+                               parentContainer = $( '#customize-theme-controls > ul' ); // @todo This should be defined elsewhere, and to be configurable
+
+                       if ( ! panel.container.parent().is( parentContainer ) ) {
+                               parentContainer.append( panel.container );
+                               panel.renderContent();
+                       }
+
+                       api.bind( 'pane-contents-reflowed', _.debounce( function() {
+                               panel._recalculateTopMargin();
+                       }, 100 ) );
+
+                       panel.deferred.embedded.resolve();
+               },
+
+               /**
+                * @since 4.1.0
+                */
+               attachEvents: function () {
+                       var meta, panel = this;
+
+                       // Expand/Collapse accordion sections on click.
+                       panel.container.find( '.accordion-section-title' ).on( 'click keydown', function( event ) {
+                               if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                                       return;
+                               }
+                               event.preventDefault(); // Keep this AFTER the key filter above
+
+                               if ( ! panel.expanded() ) {
+                                       panel.expand();
+                               }
+                       });
+
+                       // Close panel.
+                       panel.container.find( '.customize-panel-back' ).on( 'click keydown', function( event ) {
+                               if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                                       return;
+                               }
+                               event.preventDefault(); // Keep this AFTER the key filter above
+
+                               if ( panel.expanded() ) {
+                                       panel.collapse();
+                               }
+                       });
+
+                       meta = panel.container.find( '.panel-meta:first' );
+
+                       meta.find( '> .accordion-section-title .customize-help-toggle' ).on( 'click keydown', function( event ) {
+                               if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                                       return;
+                               }
+                               event.preventDefault(); // Keep this AFTER the key filter above
+
+                               meta = panel.container.find( '.panel-meta' );
+                               if ( meta.hasClass( 'cannot-expand' ) ) {
+                                       return;
+                               }
+
+                               var content = meta.find( '.customize-panel-description:first' );
+                               if ( meta.hasClass( 'open' ) ) {
+                                       meta.toggleClass( 'open' );
+                                       content.slideUp( panel.defaultExpandedArguments.duration );
+                                       $( this ).attr( 'aria-expanded', false );
+                               } else {
+                                       content.slideDown( panel.defaultExpandedArguments.duration );
+                                       meta.toggleClass( 'open' );
+                                       $( this ).attr( 'aria-expanded', true );
+                               }
+                       });
+
+               },
+
+               /**
+                * Get the sections that are associated with this panel, sorted by their priority Value.
+                *
+                * @since 4.1.0
+                *
+                * @returns {Array}
+                */
+               sections: function () {
+                       return this._children( 'panel', 'section' );
+               },
+
+               /**
+                * Return whether this panel has any active sections.
+                *
+                * @since 4.1.0
+                *
+                * @returns {boolean}
+                */
+               isContextuallyActive: function () {
+                       var panel = this,
+                               sections = panel.sections(),
+                               activeCount = 0;
+                       _( sections ).each( function ( section ) {
+                               if ( section.active() && section.isContextuallyActive() ) {
+                                       activeCount += 1;
+                               }
+                       } );
+                       return ( activeCount !== 0 );
+               },
+
+               /**
+                * Update UI to reflect expanded state
+                *
+                * @since 4.1.0
+                *
+                * @param {Boolean}  expanded
+                * @param {Object}   args
+                * @param {Boolean}  args.unchanged
+                * @param {Function} args.completeCallback
+                */
+               onChangeExpanded: function ( expanded, args ) {
+
+                       // Immediately call the complete callback if there were no changes
+                       if ( args.unchanged ) {
+                               if ( args.completeCallback ) {
+                                       args.completeCallback();
+                               }
+                               return;
+                       }
+
+                       // Note: there is a second argument 'args' passed
+                       var position, scroll,
+                               panel = this,
+                               accordionSection = panel.container.closest( '.accordion-section' ),
+                               overlay = accordionSection.closest( '.wp-full-overlay' ),
+                               container = accordionSection.closest( '.wp-full-overlay-sidebar-content' ),
+                               siblings = container.find( '.open' ),
+                               topPanel = overlay.find( '#customize-theme-controls > ul > .accordion-section > .accordion-section-title' ),
+                               backBtn = accordionSection.find( '.customize-panel-back' ),
+                               panelTitle = accordionSection.find( '.accordion-section-title' ).first(),
+                               content = accordionSection.find( '.control-panel-content' ),
+                               headerActionsHeight = $( '#customize-header-actions' ).height();
+
+                       if ( expanded ) {
+
+                               // Collapse any sibling sections/panels
+                               api.section.each( function ( section ) {
+                                       if ( panel.id !== section.panel() ) {
+                                               section.collapse( { duration: 0 } );
+                                       }
+                               });
+                               api.panel.each( function ( otherPanel ) {
+                                       if ( panel !== otherPanel ) {
+                                               otherPanel.collapse( { duration: 0 } );
+                                       }
+                               });
+
+                               content.show( 0, function() {
+                                       content.parent().show();
+                                       position = content.offset().top;
+                                       scroll = container.scrollTop();
+                                       content.css( 'margin-top', ( headerActionsHeight - position - scroll ) );
+                                       accordionSection.addClass( 'current-panel' );
+                                       overlay.addClass( 'in-sub-panel' );
+                                       container.scrollTop( 0 );
+                                       if ( args.completeCallback ) {
+                                               args.completeCallback();
+                                       }
+                               } );
+                               topPanel.attr( 'tabindex', '-1' );
+                               backBtn.attr( 'tabindex', '0' );
+                               backBtn.focus();
+                               panel._recalculateTopMargin();
+                       } else {
+                               siblings.removeClass( 'open' );
+                               accordionSection.removeClass( 'current-panel' );
+                               overlay.removeClass( 'in-sub-panel' );
+                               content.delay( 180 ).hide( 0, function() {
+                                       content.css( 'margin-top', 'inherit' ); // Reset
+                                       if ( args.completeCallback ) {
+                                               args.completeCallback();
+                                       }
+                               } );
+                               topPanel.attr( 'tabindex', '0' );
+                               backBtn.attr( 'tabindex', '-1' );
+                               panelTitle.focus();
+                               container.scrollTop( 0 );
+                       }
+               },
+
+               /**
+                * Recalculate the top margin.
+                *
+                * @since 4.4.0
+                * @private
+                */
+               _recalculateTopMargin: function() {
+                       var panel = this, headerActionsHeight, content, accordionSection;
+                       headerActionsHeight = $( '#customize-header-actions' ).height();
+                       accordionSection = panel.container.closest( '.accordion-section' );
+                       content = accordionSection.find( '.control-panel-content' );
+                       content.css( 'margin-top', ( parseInt( content.css( 'margin-top' ), 10 ) - ( content.offset().top - headerActionsHeight ) ) );
+               },
+
+               /**
+                * Render the panel from its JS template, if it exists.
+                *
+                * The panel's container must already exist in the DOM.
+                *
+                * @since 4.3.0
+                */
+               renderContent: function () {
+                       var template,
+                               panel = this;
+
+                       // Add the content to the container.
+                       if ( 0 !== $( '#tmpl-' + panel.templateSelector + '-content' ).length ) {
+                               template = wp.template( panel.templateSelector + '-content' );
+                       } else {
+                               template = wp.template( 'customize-panel-default-content' );
+                       }
+                       if ( template && panel.container ) {
+                               panel.container.find( '.accordion-sub-container' ).html( template( panel.params ) );
+                       }
+               }
+       });
+
+       /**
+        * A Customizer Control.
+        *
+        * A control provides a UI element that allows a user to modify a Customizer Setting.
+        *
+        * @see PHP class WP_Customize_Control.
+        *
+        * @class
+        * @augments wp.customize.Class
+        *
+        * @param {string} id                              Unique identifier for the control instance.
+        * @param {object} options                         Options hash for the control instance.
+        * @param {object} options.params
+        * @param {object} options.params.type             Type of control (e.g. text, radio, dropdown-pages, etc.)
+        * @param {string} options.params.content          The HTML content for the control.
+        * @param {string} options.params.priority         Order of priority to show the control within the section.
+        * @param {string} options.params.active
+        * @param {string} options.params.section          The ID of the section the control belongs to.
+        * @param {string} options.params.settings.default The ID of the setting the control relates to.
+        * @param {string} options.params.settings.data
+        * @param {string} options.params.label
+        * @param {string} options.params.description
+        * @param {string} options.params.instanceNumber Order in which this instance was created in relation to other instances.
+        */
+       api.Control = api.Class.extend({
+               defaultActiveArguments: { duration: 'fast', completeCallback: $.noop },
+
+               initialize: function( id, options ) {
+                       var control = this,
+                               nodes, radios, settings;
 
                        control.params = {};
                        $.extend( control, options || {} );
                        control.priority = new api.Value();
                        control.active = new api.Value();
                        control.activeArgumentsQueue = [];
+                       control.notifications = new api.Values({ defaultConstructor: api.Notification });
 
                        control.elements = [];
 
 
                        api.utils.bubbleChildValueChanges( control, [ 'section', 'priority', 'active' ] );
 
-                       // Associate this control with its settings when they are created
+                       /*
+                        * After all settings related to the control are available,
+                        * make them available on the control and embed the control into the page.
+                        */
                        settings = $.map( control.params.settings, function( value ) {
                                return value;
                        });
-                       api.apply( api, settings.concat( function () {
-                               var key;
 
+                       if ( 0 === settings.length ) {
+                               control.setting = null;
                                control.settings = {};
-                               for ( key in control.params.settings ) {
-                                       control.settings[ key ] = api( control.params.settings[ key ] );
-                               }
+                               control.embed();
+                       } else {
+                               api.apply( api, settings.concat( function() {
+                                       var key;
 
-                               control.setting = control.settings['default'] || null;
+                                       control.settings = {};
+                                       for ( key in control.params.settings ) {
+                                               control.settings[ key ] = api( control.params.settings[ key ] );
+                                       }
 
-                               control.embed();
-                       }) );
+                                       control.setting = control.settings['default'] || null;
+
+                                       // Add setting notifications to the control notification.
+                                       _.each( control.settings, function( setting ) {
+                                               setting.notifications.bind( 'add', function( settingNotification ) {
+                                                       var controlNotification, code, params;
+                                                       code = setting.id + ':' + settingNotification.code;
+                                                       params = _.extend(
+                                                               {},
+                                                               settingNotification,
+                                                               {
+                                                                       setting: setting.id
+                                                               }
+                                                       );
+                                                       controlNotification = new api.Notification( code, params );
+                                                       control.notifications.add( controlNotification.code, controlNotification );
+                                               } );
+                                               setting.notifications.bind( 'remove', function( settingNotification ) {
+                                                       control.notifications.remove( setting.id + ':' + settingNotification.code );
+                                               } );
+                                       } );
+
+                                       control.embed();
+                               }) );
+                       }
 
+                       // After the control is embedded on the page, invoke the "ready" method.
                        control.deferred.embedded.done( function () {
+                               /*
+                                * Note that this debounced/deferred rendering is needed for two reasons:
+                                * 1) The 'remove' event is triggered just _before_ the notification is actually removed.
+                                * 2) Improve performance when adding/removing multiple notifications at a time.
+                                */
+                               var debouncedRenderNotifications = _.debounce( function renderNotifications() {
+                                       control.renderNotifications();
+                               } );
+                               control.notifications.bind( 'add', function( notification ) {
+                                       wp.a11y.speak( notification.message, 'assertive' );
+                                       debouncedRenderNotifications();
+                               } );
+                               control.notifications.bind( 'remove', debouncedRenderNotifications );
+                               control.renderNotifications();
+
                                control.ready();
                        });
                },
                        // Watch for changes to the section state
                        inject = function ( sectionId ) {
                                var parentContainer;
-                               if ( ! sectionId ) { // @todo allow a control to be embedded without a section, for instance a control embedded in the frontend
+                               if ( ! sectionId ) { // @todo allow a control to be embedded without a section, for instance a control embedded in the front end.
                                        return;
                                }
                                // Wait for the section to be registered
                 */
                ready: function() {},
 
+               /**
+                * Get the element inside of a control's container that contains the validation error message.
+                *
+                * Control subclasses may override this to return the proper container to render notifications into.
+                * Injects the notification container for existing controls that lack the necessary container,
+                * including special handling for nav menu items and widgets.
+                *
+                * @since 4.6.0
+                * @returns {jQuery} Setting validation message element.
+                * @this {wp.customize.Control}
+                */
+               getNotificationsContainerElement: function() {
+                       var control = this, controlTitle, notificationsContainer;
+
+                       notificationsContainer = control.container.find( '.customize-control-notifications-container:first' );
+                       if ( notificationsContainer.length ) {
+                               return notificationsContainer;
+                       }
+
+                       notificationsContainer = $( '<div class="customize-control-notifications-container"></div>' );
+
+                       if ( control.container.hasClass( 'customize-control-nav_menu_item' ) ) {
+                               control.container.find( '.menu-item-settings:first' ).prepend( notificationsContainer );
+                       } else if ( control.container.hasClass( 'customize-control-widget_form' ) ) {
+                               control.container.find( '.widget-inside:first' ).prepend( notificationsContainer );
+                       } else {
+                               controlTitle = control.container.find( '.customize-control-title' );
+                               if ( controlTitle.length ) {
+                                       controlTitle.after( notificationsContainer );
+                               } else {
+                                       control.container.prepend( notificationsContainer );
+                               }
+                       }
+                       return notificationsContainer;
+               },
+
+               /**
+                * Render notifications.
+                *
+                * Renders the `control.notifications` into the control's container.
+                * Control subclasses may override this method to do their own handling
+                * of rendering notifications.
+                *
+                * @since 4.6.0
+                * @this {wp.customize.Control}
+                */
+               renderNotifications: function() {
+                       var control = this, container, notifications, hasError = false;
+                       container = control.getNotificationsContainerElement();
+                       if ( ! container || ! container.length ) {
+                               return;
+                       }
+                       notifications = [];
+                       control.notifications.each( function( notification ) {
+                               notifications.push( notification );
+                               if ( 'error' === notification.type ) {
+                                       hasError = true;
+                               }
+                       } );
+
+                       if ( 0 === notifications.length ) {
+                               container.stop().slideUp( 'fast' );
+                       } else {
+                               container.stop().slideDown( 'fast', null, function() {
+                                       $( this ).css( 'height', 'auto' );
+                               } );
+                       }
+
+                       if ( ! control.notificationsTemplate ) {
+                               control.notificationsTemplate = wp.template( 'customize-control-notifications' );
+                       }
+
+                       control.container.toggleClass( 'has-notifications', 0 !== notifications.length );
+                       control.container.toggleClass( 'has-error', hasError );
+                       container.empty().append( $.trim(
+                               control.notificationsTemplate( { notifications: notifications, altNotice: Boolean( control.altNotice ) } )
+                       ) );
+               },
+
                /**
                 * Normal controls do not expand, so just expand its parent
                 *
                 * @param {Callback} args.completeCallback
                 */
                onChangeActive: function ( active, args ) {
-                       if ( ! $.contains( document, this.container ) ) {
+                       if ( args.unchanged ) {
+                               if ( args.completeCallback ) {
+                                       args.completeCallback();
+                               }
+                               return;
+                       }
+
+                       if ( ! $.contains( document, this.container[0] ) ) {
                                // jQuery.fn.slideUp is not hiding an element if it is not in the DOM
                                this.container.toggle( active );
                                if ( args.completeCallback ) {
                                        control.setting.set( picker.wpColorPicker('color') );
                                },
                                clear: function() {
-                                       control.setting.set( false );
+                                       control.setting.set( '' );
                                }
                        });
 
        });
 
        /**
-        * An upload control, which utilizes the media modal.
+        * A control that implements the media modal.
         *
         * @class
         * @augments wp.customize.Control
         * @augments wp.customize.Class
         */
-       api.UploadControl = api.Control.extend({
+       api.MediaControl = api.Control.extend({
 
                /**
                 * When the control's DOM structure is ready,
                ready: function() {
                        var control = this;
                        // Shortcut so that we don't have to use _.bind every time we add a callback.
-                       _.bindAll( control, 'restoreDefault', 'removeFile', 'openFrame', 'select' );
+                       _.bindAll( control, 'restoreDefault', 'removeFile', 'openFrame', 'select', 'pausePlayer' );
 
                        // Bind events, with delegation to facilitate re-rendering.
                        control.container.on( 'click keydown', '.upload-button', control.openFrame );
+                       control.container.on( 'click keydown', '.upload-button', control.pausePlayer );
                        control.container.on( 'click keydown', '.thumbnail-image img', control.openFrame );
                        control.container.on( 'click keydown', '.default-button', control.restoreDefault );
+                       control.container.on( 'click keydown', '.remove-button', control.pausePlayer );
                        control.container.on( 'click keydown', '.remove-button', control.removeFile );
+                       control.container.on( 'click keydown', '.remove-button', control.cleanupPlayer );
+
+                       // Resize the player controls when it becomes visible (ie when section is expanded)
+                       api.section( control.section() ).container
+                               .on( 'expanded', function() {
+                                       if ( control.player ) {
+                                               control.player.setControlsSize();
+                                       }
+                               })
+                               .on( 'collapsed', function() {
+                                       control.pausePlayer();
+                               });
+
+                       /**
+                        * Set attachment data and render content.
+                        *
+                        * Note that BackgroundImage.prototype.ready applies this ready method
+                        * to itself. Since BackgroundImage is an UploadControl, the value
+                        * is the attachment URL instead of the attachment ID. In this case
+                        * we skip fetching the attachment data because we have no ID available,
+                        * and it is the responsibility of the UploadControl to set the control's
+                        * attachmentData before calling the renderContent method.
+                        *
+                        * @param {number|string} value Attachment
+                        */
+                       function setAttachmentDataAndRenderContent( value ) {
+                               var hasAttachmentData = $.Deferred();
+
+                               if ( control.extended( api.UploadControl ) ) {
+                                       hasAttachmentData.resolve();
+                               } else {
+                                       value = parseInt( value, 10 );
+                                       if ( _.isNaN( value ) || value <= 0 ) {
+                                               delete control.params.attachment;
+                                               hasAttachmentData.resolve();
+                                       } else if ( control.params.attachment && control.params.attachment.id === value ) {
+                                               hasAttachmentData.resolve();
+                                       }
+                               }
 
-                       // Re-render whenever the control's setting changes.
-                       control.setting.bind( function () { control.renderContent(); } );
+                               // Fetch the attachment data.
+                               if ( 'pending' === hasAttachmentData.state() ) {
+                                       wp.media.attachment( value ).fetch().done( function() {
+                                               control.params.attachment = this.attributes;
+                                               hasAttachmentData.resolve();
+
+                                               // Send attachment information to the preview for possible use in `postMessage` transport.
+                                               wp.customize.previewer.send( control.setting.id + '-attachment-data', this.attributes );
+                                       } );
+                               }
+
+                               hasAttachmentData.done( function() {
+                                       control.renderContent();
+                               } );
+                       }
+
+                       // Ensure attachment data is initially set (for dynamically-instantiated controls).
+                       setAttachmentDataAndRenderContent( control.setting() );
+
+                       // Update the attachment data and re-render the control when the setting changes.
+                       control.setting.bind( setAttachmentDataAndRenderContent );
+               },
+
+               pausePlayer: function () {
+                       this.player && this.player.pause();
+               },
+
+               cleanupPlayer: function () {
+                       this.player && wp.media.mixin.removePlayer( this.player );
                },
 
                /**
                                this.initFrame();
                        }
 
-                       this.frame.open();
+                       this.frame.open();
+               },
+
+               /**
+                * Create a media modal select frame, and store it so the instance can be reused when needed.
+                */
+               initFrame: function() {
+                       this.frame = wp.media({
+                               button: {
+                                       text: this.params.button_labels.frame_button
+                               },
+                               states: [
+                                       new wp.media.controller.Library({
+                                               title:     this.params.button_labels.frame_title,
+                                               library:   wp.media.query({ type: this.params.mime_type }),
+                                               multiple:  false,
+                                               date:      false
+                                       })
+                               ]
+                       });
+
+                       // When a file is selected, run a callback.
+                       this.frame.on( 'select', this.select );
+               },
+
+               /**
+                * Callback handler for when an attachment is selected in the media modal.
+                * Gets the selected image information, and sets it within the control.
+                */
+               select: function() {
+                       // Get the attachment from the modal frame.
+                       var node,
+                               attachment = this.frame.state().get( 'selection' ).first().toJSON(),
+                               mejsSettings = window._wpmejsSettings || {};
+
+                       this.params.attachment = attachment;
+
+                       // Set the Customizer setting; the callback takes care of rendering.
+                       this.setting( attachment.id );
+                       node = this.container.find( 'audio, video' ).get(0);
+
+                       // Initialize audio/video previews.
+                       if ( node ) {
+                               this.player = new MediaElementPlayer( node, mejsSettings );
+                       } else {
+                               this.cleanupPlayer();
+                       }
+               },
+
+               /**
+                * Reset the setting to the default value.
+                */
+               restoreDefault: function( event ) {
+                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                               return;
+                       }
+                       event.preventDefault();
+
+                       this.params.attachment = this.params.defaultAttachment;
+                       this.setting( this.params.defaultAttachment.url );
+               },
+
+               /**
+                * Called when the "Remove" link is clicked. Empties the setting.
+                *
+                * @param {object} event jQuery Event object
+                */
+               removeFile: function( event ) {
+                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                               return;
+                       }
+                       event.preventDefault();
+
+                       this.params.attachment = {};
+                       this.setting( '' );
+                       this.renderContent(); // Not bound to setting change when emptying.
+               }
+       });
+
+       /**
+        * An upload control, which utilizes the media modal.
+        *
+        * @class
+        * @augments wp.customize.MediaControl
+        * @augments wp.customize.Control
+        * @augments wp.customize.Class
+        */
+       api.UploadControl = api.MediaControl.extend({
+
+               /**
+                * Callback handler for when an attachment is selected in the media modal.
+                * Gets the selected image information, and sets it within the control.
+                */
+               select: function() {
+                       // Get the attachment from the modal frame.
+                       var node,
+                               attachment = this.frame.state().get( 'selection' ).first().toJSON(),
+                               mejsSettings = window._wpmejsSettings || {};
+
+                       this.params.attachment = attachment;
+
+                       // Set the Customizer setting; the callback takes care of rendering.
+                       this.setting( attachment.url );
+                       node = this.container.find( 'audio, video' ).get(0);
+
+                       // Initialize audio/video previews.
+                       if ( node ) {
+                               this.player = new MediaElementPlayer( node, mejsSettings );
+                       } else {
+                               this.cleanupPlayer();
+                       }
+               },
+
+               // @deprecated
+               success: function() {},
+
+               // @deprecated
+               removerVisibility: function() {}
+       });
+
+       /**
+        * A control for uploading images.
+        *
+        * This control no longer needs to do anything more
+        * than what the upload control does in JS.
+        *
+        * @class
+        * @augments wp.customize.UploadControl
+        * @augments wp.customize.MediaControl
+        * @augments wp.customize.Control
+        * @augments wp.customize.Class
+        */
+       api.ImageControl = api.UploadControl.extend({
+               // @deprecated
+               thumbnailSrc: function() {}
+       });
+
+       /**
+        * A control for uploading background images.
+        *
+        * @class
+        * @augments wp.customize.UploadControl
+        * @augments wp.customize.MediaControl
+        * @augments wp.customize.Control
+        * @augments wp.customize.Class
+        */
+       api.BackgroundControl = api.UploadControl.extend({
+
+               /**
+                * When the control's DOM structure is ready,
+                * set up internal event bindings.
+                */
+               ready: function() {
+                       api.UploadControl.prototype.ready.apply( this, arguments );
+               },
+
+               /**
+                * Callback handler for when an attachment is selected in the media modal.
+                * Does an additional AJAX request for setting the background context.
+                */
+               select: function() {
+                       api.UploadControl.prototype.select.apply( this, arguments );
+
+                       wp.ajax.post( 'custom-background-add', {
+                               nonce: _wpCustomizeBackground.nonces.add,
+                               wp_customize: 'on',
+                               theme: api.settings.theme.stylesheet,
+                               attachment_id: this.params.attachment.id
+                       } );
+               }
+       });
+
+       /**
+        * A control for selecting and cropping an image.
+        *
+        * @class
+        * @augments wp.customize.MediaControl
+        * @augments wp.customize.Control
+        * @augments wp.customize.Class
+        */
+       api.CroppedImageControl = api.MediaControl.extend({
+
+               /**
+                * Open the media modal to the library state.
+                */
+               openFrame: function( event ) {
+                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                               return;
+                       }
+
+                       this.initFrame();
+                       this.frame.setState( 'library' ).open();
                },
 
                /**
                 * Create a media modal select frame, and store it so the instance can be reused when needed.
                 */
                initFrame: function() {
+                       var l10n = _wpMediaViewsL10n;
+
                        this.frame = wp.media({
                                button: {
-                                       text: this.params.button_labels.frame_button
+                                       text: l10n.select,
+                                       close: false
                                },
                                states: [
                                        new wp.media.controller.Library({
-                                               title:     this.params.button_labels.frame_title,
-                                               library:   wp.media.query({ type: this.params.mime_type }),
-                                               multiple:  false,
-                                               date:      false
+                                               title: this.params.button_labels.frame_title,
+                                               library: wp.media.query({ type: 'image' }),
+                                               multiple: false,
+                                               date: false,
+                                               priority: 20,
+                                               suggestedWidth: this.params.width,
+                                               suggestedHeight: this.params.height
+                                       }),
+                                       new wp.media.controller.CustomizeImageCropper({
+                                               imgSelectOptions: this.calculateImageSelectOptions,
+                                               control: this
                                        })
                                ]
                        });
 
-                       // When a file is selected, run a callback.
-                       this.frame.on( 'select', this.select );
+                       this.frame.on( 'select', this.onSelect, this );
+                       this.frame.on( 'cropped', this.onCropped, this );
+                       this.frame.on( 'skippedcrop', this.onSkippedCrop, this );
                },
 
                /**
-                * Callback handler for when an attachment is selected in the media modal.
-                * Gets the selected image information, and sets it within the control.
+                * After an image is selected in the media modal, switch to the cropper
+                * state if the image isn't the right size.
                 */
-               select: function() {
-                       // Get the attachment from the modal frame.
+               onSelect: function() {
                        var attachment = this.frame.state().get( 'selection' ).first().toJSON();
 
-                       this.params.attachment = attachment;
+                       if ( this.params.width === attachment.width && this.params.height === attachment.height && ! this.params.flex_width && ! this.params.flex_height ) {
+                               this.setImageFromAttachment( attachment );
+                               this.frame.close();
+                       } else {
+                               this.frame.setState( 'cropper' );
+                       }
+               },
 
-                       // Set the Customizer setting; the callback takes care of rendering.
-                       this.setting( attachment.url );
+               /**
+                * After the image has been cropped, apply the cropped image data to the setting.
+                *
+                * @param {object} croppedImage Cropped attachment data.
+                */
+               onCropped: function( croppedImage ) {
+                       this.setImageFromAttachment( croppedImage );
                },
 
                /**
-                * Reset the setting to the default value.
+                * Returns a set of options, computed from the attached image data and
+                * control-specific data, to be fed to the imgAreaSelect plugin in
+                * wp.media.view.Cropper.
+                *
+                * @param {wp.media.model.Attachment} attachment
+                * @param {wp.media.controller.Cropper} controller
+                * @returns {Object} Options
                 */
-               restoreDefault: function( event ) {
-                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
-                               return;
+               calculateImageSelectOptions: function( attachment, controller ) {
+                       var control    = controller.get( 'control' ),
+                               flexWidth  = !! parseInt( control.params.flex_width, 10 ),
+                               flexHeight = !! parseInt( control.params.flex_height, 10 ),
+                               realWidth  = attachment.get( 'width' ),
+                               realHeight = attachment.get( 'height' ),
+                               xInit = parseInt( control.params.width, 10 ),
+                               yInit = parseInt( control.params.height, 10 ),
+                               ratio = xInit / yInit,
+                               xImg  = xInit,
+                               yImg  = yInit,
+                               x1, y1, imgSelectOptions;
+
+                       controller.set( 'canSkipCrop', ! control.mustBeCropped( flexWidth, flexHeight, xInit, yInit, realWidth, realHeight ) );
+
+                       if ( realWidth / realHeight > ratio ) {
+                               yInit = realHeight;
+                               xInit = yInit * ratio;
+                       } else {
+                               xInit = realWidth;
+                               yInit = xInit / ratio;
                        }
-                       event.preventDefault();
 
-                       this.params.attachment = this.params.defaultAttachment;
-                       this.setting( this.params.defaultAttachment.url );
-               },
+                       x1 = ( realWidth - xInit ) / 2;
+                       y1 = ( realHeight - yInit ) / 2;
+
+                       imgSelectOptions = {
+                               handles: true,
+                               keys: true,
+                               instance: true,
+                               persistent: true,
+                               imageWidth: realWidth,
+                               imageHeight: realHeight,
+                               minWidth: xImg > xInit ? xInit : xImg,
+                               minHeight: yImg > yInit ? yInit : yImg,
+                               x1: x1,
+                               y1: y1,
+                               x2: xInit + x1,
+                               y2: yInit + y1
+                       };
+
+                       if ( flexHeight === false && flexWidth === false ) {
+                               imgSelectOptions.aspectRatio = xInit + ':' + yInit;
+                       }
+
+                       if ( true === flexHeight ) {
+                               delete imgSelectOptions.minHeight;
+                               imgSelectOptions.maxWidth = realWidth;
+                       }
+
+                       if ( true === flexWidth ) {
+                               delete imgSelectOptions.minWidth;
+                               imgSelectOptions.maxHeight = realHeight;
+                       }
+
+                       return imgSelectOptions;
+               },
 
                /**
-                * Called when the "Remove" link is clicked. Empties the setting.
+                * Return whether the image must be cropped, based on required dimensions.
                 *
-                * @param {object} event jQuery Event object
+                * @param {bool} flexW
+                * @param {bool} flexH
+                * @param {int}  dstW
+                * @param {int}  dstH
+                * @param {int}  imgW
+                * @param {int}  imgH
+                * @return {bool}
                 */
-               removeFile: function( event ) {
-                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
-                               return;
+               mustBeCropped: function( flexW, flexH, dstW, dstH, imgW, imgH ) {
+                       if ( true === flexW && true === flexH ) {
+                               return false;
                        }
-                       event.preventDefault();
 
-                       this.params.attachment = {};
-                       this.setting( '' );
-                       this.renderContent(); // Not bound to setting change when emptying.
+                       if ( true === flexW && dstH === imgH ) {
+                               return false;
+                       }
+
+                       if ( true === flexH && dstW === imgW ) {
+                               return false;
+                       }
+
+                       if ( dstW === imgW && dstH === imgH ) {
+                               return false;
+                       }
+
+                       if ( imgW <= dstW ) {
+                               return false;
+                       }
+
+                       return true;
                },
 
-               // @deprecated
-               success: function() {},
+               /**
+                * If cropping was skipped, apply the image data directly to the setting.
+                */
+               onSkippedCrop: function() {
+                       var attachment = this.frame.state().get( 'selection' ).first().toJSON();
+                       this.setImageFromAttachment( attachment );
+               },
 
-               // @deprecated
-               removerVisibility: function() {}
-       });
+               /**
+                * Updates the setting and re-renders the control UI.
+                *
+                * @param {object} attachment
+                */
+               setImageFromAttachment: function( attachment ) {
+                       this.params.attachment = attachment;
 
-       /**
-        * A control for uploading images.
-        *
-        * This control no longer needs to do anything more
-        * than what the upload control does in JS.
-        *
-        * @class
-        * @augments wp.customize.UploadControl
-        * @augments wp.customize.Control
-        * @augments wp.customize.Class
-        */
-       api.ImageControl = api.UploadControl.extend({
-               // @deprecated
-               thumbnailSrc: function() {}
+                       // Set the Customizer setting; the callback takes care of rendering.
+                       this.setting( attachment.id );
+               }
        });
 
        /**
-        * A control for uploading background images.
+        * A control for selecting and cropping Site Icons.
         *
         * @class
-        * @augments wp.customize.UploadControl
+        * @augments wp.customize.CroppedImageControl
+        * @augments wp.customize.MediaControl
         * @augments wp.customize.Control
         * @augments wp.customize.Class
         */
-       api.BackgroundControl = api.UploadControl.extend({
+       api.SiteIconControl = api.CroppedImageControl.extend({
 
                /**
-                * When the control's DOM structure is ready,
-                * set up internal event bindings.
+                * Create a media modal select frame, and store it so the instance can be reused when needed.
                 */
-               ready: function() {
-                       api.UploadControl.prototype.ready.apply( this, arguments );
+               initFrame: function() {
+                       var l10n = _wpMediaViewsL10n;
+
+                       this.frame = wp.media({
+                               button: {
+                                       text: l10n.select,
+                                       close: false
+                               },
+                               states: [
+                                       new wp.media.controller.Library({
+                                               title: this.params.button_labels.frame_title,
+                                               library: wp.media.query({ type: 'image' }),
+                                               multiple: false,
+                                               date: false,
+                                               priority: 20,
+                                               suggestedWidth: this.params.width,
+                                               suggestedHeight: this.params.height
+                                       }),
+                                       new wp.media.controller.SiteIconCropper({
+                                               imgSelectOptions: this.calculateImageSelectOptions,
+                                               control: this
+                                       })
+                               ]
+                       });
+
+                       this.frame.on( 'select', this.onSelect, this );
+                       this.frame.on( 'cropped', this.onCropped, this );
+                       this.frame.on( 'skippedcrop', this.onSkippedCrop, this );
                },
 
                /**
-                * Callback handler for when an attachment is selected in the media modal.
-                * Does an additional AJAX request for setting the background context.
+                * After an image is selected in the media modal, switch to the cropper
+                * state if the image isn't the right size.
                 */
-               select: function() {
-                       api.UploadControl.prototype.select.apply( this, arguments );
+               onSelect: function() {
+                       var attachment = this.frame.state().get( 'selection' ).first().toJSON(),
+                               controller = this;
+
+                       if ( this.params.width === attachment.width && this.params.height === attachment.height && ! this.params.flex_width && ! this.params.flex_height ) {
+                               wp.ajax.post( 'crop-image', {
+                                       nonce: attachment.nonces.edit,
+                                       id: attachment.id,
+                                       context: 'site-icon',
+                                       cropDetails: {
+                                               x1: 0,
+                                               y1: 0,
+                                               width: this.params.width,
+                                               height: this.params.height,
+                                               dst_width: this.params.width,
+                                               dst_height: this.params.height
+                                       }
+                               } ).done( function( croppedImage ) {
+                                       controller.setImageFromAttachment( croppedImage );
+                                       controller.frame.close();
+                               } ).fail( function() {
+                                       controller.frame.trigger('content:error:crop');
+                               } );
+                       } else {
+                               this.frame.setState( 'cropper' );
+                       }
+               },
 
-                       wp.ajax.post( 'custom-background-add', {
-                               nonce: _wpCustomizeBackground.nonces.add,
-                               wp_customize: 'on',
-                               theme: api.settings.theme.stylesheet,
-                               attachment_id: this.params.attachment.id
+               /**
+                * Updates the setting and re-renders the control UI.
+                *
+                * @param {object} attachment
+                */
+               setImageFromAttachment: function( attachment ) {
+                       var sizes = [ 'site_icon-32', 'thumbnail', 'full' ],
+                               icon;
+
+                       _.each( sizes, function( size ) {
+                               if ( ! icon && ! _.isUndefined ( attachment.sizes[ size ] ) ) {
+                                       icon = attachment.sizes[ size ];
+                               }
                        } );
+
+                       this.params.attachment = attachment;
+
+                       // Set the Customizer setting; the callback takes care of rendering.
+                       this.setting( attachment.id );
+
+                       // Update the icon in-browser.
+                       $( 'link[sizes="32x32"]' ).attr( 'href', icon.url );
+               },
+
+               /**
+                * Called when the "Remove" link is clicked. Empties the setting.
+                *
+                * @param {object} event jQuery Event object
+                */
+               removeFile: function( event ) {
+                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                               return;
+                       }
+                       event.preventDefault();
+
+                       this.params.attachment = {};
+                       this.setting( '' );
+                       this.renderContent(); // Not bound to setting change when emptying.
+                       $( 'link[rel="icon"]' ).attr( 'href', '' );
                }
        });
 
         */
        api.HeaderControl = api.Control.extend({
                ready: function() {
-                       this.btnRemove        = $('#customize-control-header_image .actions .remove');
-                       this.btnNew           = $('#customize-control-header_image .actions .new');
+                       this.btnRemove = $('#customize-control-header_image .actions .remove');
+                       this.btnNew    = $('#customize-control-header_image .actions .new');
 
                        _.bindAll(this, 'openMedia', 'removeImage');
 
                        this.btnNew.on( 'click', this.openMedia );
                        this.btnRemove.on( 'click', this.removeImage );
 
-                       api.HeaderTool.currentHeader = new api.HeaderTool.ImageModel();
+                       api.HeaderTool.currentHeader = this.getInitialHeaderImage();
 
                        new api.HeaderTool.CurrentView({
                                model: api.HeaderTool.currentHeader,
                                api.HeaderTool.UploadsList,
                                api.HeaderTool.DefaultsList
                        ]);
+
+                       // Ensure custom-header-crop Ajax requests bootstrap the Customizer to activate the previewed theme.
+                       wp.media.controller.Cropper.prototype.defaults.doCropArgs.wp_customize = 'on';
+                       wp.media.controller.Cropper.prototype.defaults.doCropArgs.theme = api.settings.theme.stylesheet;
+               },
+
+               /**
+                * Returns a new instance of api.HeaderTool.ImageModel based on the currently
+                * saved header image (if any).
+                *
+                * @since 4.2.0
+                *
+                * @returns {Object} Options
+                */
+               getInitialHeaderImage: function() {
+                       if ( ! api.get().header_image || ! api.get().header_image_data || _.contains( [ 'remove-header', 'random-default-image', 'random-uploaded-image' ], api.get().header_image ) ) {
+                               return new api.HeaderTool.ImageModel();
+                       }
+
+                       // Get the matching uploaded image object.
+                       var currentHeaderObject = _.find( _wpCustomizeHeader.uploads, function( imageObj ) {
+                               return ( imageObj.attachment_id === api.get().header_image_data.attachment_id );
+                       } );
+                       // Fall back to raw current header image.
+                       if ( ! currentHeaderObject ) {
+                               currentHeaderObject = {
+                                       url: api.get().header_image,
+                                       thumbnail_url: api.get().header_image,
+                                       attachment_id: api.get().header_image_data.attachment_id
+                               };
+                       }
+
+                       return new api.HeaderTool.ImageModel({
+                               header: currentHeaderObject,
+                               choice: currentHeaderObject.url.split( '/' ).pop()
+                       });
                },
 
                /**
                 * @param {object} croppedImage Cropped attachment data.
                 */
                onCropped: function(croppedImage) {
-                       var url = croppedImage.post_content,
+                       var url = croppedImage.url,
                                attachmentId = croppedImage.attachment_id,
                                w = croppedImage.width,
                                h = croppedImage.height;
                        api.HeaderTool.currentHeader.trigger('hide');
                        api.HeaderTool.CombinedList.trigger('control:removeImage');
                }
-
+
+       });
+
+       /**
+        * wp.customize.ThemeControl
+        *
+        * @constructor
+        * @augments wp.customize.Control
+        * @augments wp.customize.Class
+        */
+       api.ThemeControl = api.Control.extend({
+
+               touchDrag: false,
+               isRendered: false,
+
+               /**
+                * Defer rendering the theme control until the section is displayed.
+                *
+                * @since 4.2.0
+                */
+               renderContent: function () {
+                       var control = this,
+                               renderContentArgs = arguments;
+
+                       api.section( control.section(), function( section ) {
+                               if ( section.expanded() ) {
+                                       api.Control.prototype.renderContent.apply( control, renderContentArgs );
+                                       control.isRendered = true;
+                               } else {
+                                       section.expanded.bind( function( expanded ) {
+                                               if ( expanded && ! control.isRendered ) {
+                                                       api.Control.prototype.renderContent.apply( control, renderContentArgs );
+                                                       control.isRendered = true;
+                                               }
+                                       } );
+                               }
+                       } );
+               },
+
+               /**
+                * @since 4.2.0
+                */
+               ready: function() {
+                       var control = this;
+
+                       control.container.on( 'touchmove', '.theme', function() {
+                               control.touchDrag = true;
+                       });
+
+                       // Bind details view trigger.
+                       control.container.on( 'click keydown touchend', '.theme', function( event ) {
+                               if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                                       return;
+                               }
+
+                               // Bail if the user scrolled on a touch device.
+                               if ( control.touchDrag === true ) {
+                                       return control.touchDrag = false;
+                               }
+
+                               // Prevent the modal from showing when the user clicks the action button.
+                               if ( $( event.target ).is( '.theme-actions .button' ) ) {
+                                       return;
+                               }
+
+                               var previewUrl = $( this ).data( 'previewUrl' );
+
+                               $( '.wp-full-overlay' ).addClass( 'customize-loading' );
+
+                               window.parent.location = previewUrl;
+                       });
+
+                       control.container.on( 'click keydown', '.theme-actions .theme-details', function( event ) {
+                               if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
+                                       return;
+                               }
+
+                               event.preventDefault(); // Keep this AFTER the key filter above
+
+                               api.section( control.section() ).showDetails( control.params.theme );
+                       });
+
+                       control.container.on( 'render-screenshot', function() {
+                               var $screenshot = $( this ).find( 'img' ),
+                                       source = $screenshot.data( 'src' );
+
+                               if ( source ) {
+                                       $screenshot.attr( 'src', source );
+                               }
+                       });
+               },
+
+               /**
+                * Show or hide the theme based on the presence of the term in the title, description, and author.
+                *
+                * @since 4.2.0
+                */
+               filter: function( term ) {
+                       var control = this,
+                               haystack = control.params.theme.name + ' ' +
+                                       control.params.theme.description + ' ' +
+                                       control.params.theme.tags + ' ' +
+                                       control.params.theme.author;
+                       haystack = haystack.toLowerCase().replace( '-', ' ' );
+                       if ( -1 !== haystack.search( term ) ) {
+                               control.activate();
+                       } else {
+                               control.deactivate();
+                       }
+               }
        });
 
        // Change objects contained within the main customize object to Settings.
        api.panel = new api.Values({ defaultConstructor: api.Panel });
 
        /**
+        * An object that fetches a preview in the background of the document, which
+        * allows for seamless replacement of an existing preview.
+        *
         * @class
         * @augments wp.customize.Messenger
         * @augments wp.customize.Class
        api.PreviewFrame = api.Messenger.extend({
                sensitivity: 2000,
 
+               /**
+                * Initialize the PreviewFrame.
+                *
+                * @param {object} params.container
+                * @param {object} params.signature
+                * @param {object} params.previewUrl
+                * @param {object} params.query
+                * @param {object} options
+                */
                initialize: function( params, options ) {
                        var deferred = $.Deferred();
 
-                       // This is the promise object.
+                       /*
+                        * Make the instance of the PreviewFrame the promise object
+                        * so other objects can easily interact with it.
+                        */
                        deferred.promise( this );
 
                        this.container = params.container;
                        this.run( deferred );
                },
 
+               /**
+                * Run the preview request.
+                *
+                * @param {object} deferred jQuery Deferred object to be resolved with
+                *                          the request.
+                */
                run: function( deferred ) {
                        var self   = this,
                                loaded = false,
                        this.bind( 'ready', this._ready );
 
                        this.bind( 'ready', function ( data ) {
+
+                               this.container.addClass( 'iframe-ready' );
+
                                if ( ! data ) {
                                        return;
                                }
                                _( constructs ).each( function ( activeConstructs, type ) {
                                        api[ type ].each( function ( construct, id ) {
                                                var active = !! ( activeConstructs && activeConstructs[ id ] );
-                                               construct.active( active );
+                                               if ( active ) {
+                                                       construct.activate();
+                                               } else {
+                                                       construct.deactivate();
+                                               }
                                        } );
                                } );
+
+                               if ( data.settingValidities ) {
+                                       api._handleSettingValidities( {
+                                               settingValidities: data.settingValidities,
+                                               focusInvalidControl: false
+                                       } );
+                               }
                        } );
 
                        this.request = $.ajax( this.previewUrl(), {
                                response = response.slice( 0, index ) + response.slice( index + signature.length );
 
                                // Create the iframe and inject the html content.
-                               self.iframe = $('<iframe />').appendTo( self.container );
+                               self.iframe = $( '<iframe />', { 'title': api.l10n.previewIframeTitle } ).appendTo( self.container );
 
                                // Bind load event after the iframe has been added to the page;
                                // otherwise it will fire when injected into the DOM.
                                deferred.rejectWith( self, [ 'logged out' ] );
                        };
 
-                       if ( this.triedLogin )
+                       if ( this.triedLogin ) {
                                return reject();
+                       }
 
                        // Check if we have an admin cookie.
                        $.get( api.settings.url.ajax, {
                        }).fail( reject ).done( function( response ) {
                                var iframe;
 
-                               if ( '1' !== response )
+                               if ( '1' !== response ) {
                                        reject();
+                               }
 
-                               iframe = $('<iframe src="' + self.previewUrl() + '" />').hide();
+                               iframe = $( '<iframe />', { 'src': self.previewUrl(), 'title': api.l10n.previewIframeTitle } ).hide();
                                iframe.appendTo( self.container );
-                               iframe.load( function() {
+                               iframe.on( 'load', function() {
                                        self.triedLogin = true;
 
                                        iframe.remove();
                tmpl = api.settings.documentTitleTmpl;
                title = tmpl.replace( '%s', documentTitle );
                document.title = title;
-               if ( window !== window.parent ) {
-                       window.parent.document.title = document.title;
-               }
+               api.trigger( 'title', title );
        };
 
        /**
                refreshBuffer: 250,
 
                /**
-                * Requires params:
-                *  - container  - a selector or jQuery element
-                *  - previewUrl - the URL of preview frame
+                * @param {array}  params.allowedUrls
+                * @param {string} params.container   A selector or jQuery element for the preview
+                *                                    frame to be placed.
+                * @param {string} params.form
+                * @param {string} params.previewUrl  The URL to preview.
+                * @param {string} params.signature
+                * @param {object} options
                 */
                initialize: function( params, options ) {
                        var self = this,
 
                        // Limit the URL to internal, front-end links.
                        //
-                       // If the frontend and the admin are served from the same domain, load the
+                       // If the front end and the admin are served from the same domain, load the
                        // preview over ssl if the Customizer is being loaded over ssl. This avoids
-                       // insecure content warnings. This is not attempted if the admin and frontend
-                       // are on different domains to avoid the case where the frontend doesn't have
+                       // insecure content warnings. This is not attempted if the admin and front end
+                       // are on different domains to avoid the case where the front end doesn't have
                        // ssl certs.
 
                        this.add( 'previewUrl', params.previewUrl ).setter( function( to ) {
                        } );
                },
 
+               /**
+                * Query string data sent with each preview request.
+                *
+                * @abstract
+                */
                query: function() {},
 
                abort: function() {
                        }
                },
 
+               /**
+                * Refresh the preview.
+                */
                refresh: function() {
                        var self = this;
 
+                       // Display loading indicator
+                       this.send( 'loading-initiated' );
+
                        this.abort();
 
                        this.loading = new api.PreviewFrame({
                        });
 
                        this.loading.fail( function( reason, location ) {
-                               if ( 'redirect' === reason && location )
+                               self.send( 'loading-failed' );
+                               if ( 'redirect' === reason && location ) {
                                        self.previewUrl( location );
+                               }
 
                                if ( 'logged out' === reason ) {
                                        if ( self.preview ) {
                                        self.login().done( self.refresh );
                                }
 
-                               if ( 'cheatin' === reason )
+                               if ( 'cheatin' === reason ) {
                                        self.cheatin();
+                               }
                        });
                },
 
                                url:     api.settings.url.login
                        });
 
-                       iframe = $('<iframe src="' + api.settings.url.login + '" />').appendTo( this.container );
+                       iframe = $( '<iframe />', { 'src': api.settings.url.login, 'title': api.l10n.loginIframeTitle } ).appendTo( this.container );
 
                        messenger.targetWindow( iframe[0].contentWindow );
 
-                       messenger.bind( 'login', function() {
-                               iframe.remove();
-                               messenger.destroy();
-                               delete previewer._login;
-                               deferred.resolve();
+                       messenger.bind( 'login', function () {
+                               var refreshNonces = previewer.refreshNonces();
+
+                               refreshNonces.always( function() {
+                                       iframe.remove();
+                                       messenger.destroy();
+                                       delete previewer._login;
+                               });
+
+                               refreshNonces.done( function() {
+                                       deferred.resolve();
+                               });
+
+                               refreshNonces.fail( function() {
+                                       previewer.cheatin();
+                                       deferred.reject();
+                               });
                        });
 
                        return this._login;
                },
 
                cheatin: function() {
-                       $( document.body ).empty().addClass('cheatin').append( '<p>' + api.l10n.cheatin + '</p>' );
+                       $( document.body ).empty().addClass( 'cheatin' ).append(
+                               '<h1>' + api.l10n.cheatin + '</h1>' +
+                               '<p>' + api.l10n.notAllowed + '</p>'
+                       );
+               },
+
+               refreshNonces: function() {
+                       var request, deferred = $.Deferred();
+
+                       deferred.promise();
+
+                       request = wp.ajax.post( 'customize_refresh_nonces', {
+                               wp_customize: 'on',
+                               theme: api.settings.theme.stylesheet
+                       });
+
+                       request.done( function( response ) {
+                               api.trigger( 'nonce-refresh', response );
+                               deferred.resolve();
+                       });
+
+                       request.fail( function() {
+                               deferred.reject();
+                       });
+
+                       return deferred;
                }
        });
 
+       api.settingConstructor = {};
        api.controlConstructor = {
-               color:  api.ColorControl,
-               upload: api.UploadControl,
-               image:  api.ImageControl,
-               header: api.HeaderControl,
-               background: api.BackgroundControl
+               color:         api.ColorControl,
+               media:         api.MediaControl,
+               upload:        api.UploadControl,
+               image:         api.ImageControl,
+               cropped_image: api.CroppedImageControl,
+               site_icon:     api.SiteIconControl,
+               header:        api.HeaderControl,
+               background:    api.BackgroundControl,
+               theme:         api.ThemeControl
        };
        api.panelConstructor = {};
-       api.sectionConstructor = {};
+       api.sectionConstructor = {
+               themes: api.ThemesSection
+       };
+
+       /**
+        * Handle setting_validities in an error response for the customize-save request.
+        *
+        * Add notifications to the settings and focus on the first control that has an invalid setting.
+        *
+        * @since 4.6.0
+        * @private
+        *
+        * @param {object}  args
+        * @param {object}  args.settingValidities
+        * @param {boolean} [args.focusInvalidControl=false]
+        * @returns {void}
+        */
+       api._handleSettingValidities = function handleSettingValidities( args ) {
+               var invalidSettingControls, invalidSettings = [], wasFocused = false;
+
+               // Find the controls that correspond to each invalid setting.
+               _.each( args.settingValidities, function( validity, settingId ) {
+                       var setting = api( settingId );
+                       if ( setting ) {
+
+                               // Add notifications for invalidities.
+                               if ( _.isObject( validity ) ) {
+                                       _.each( validity, function( params, code ) {
+                                               var notification = new api.Notification( code, params ), existingNotification, needsReplacement = false;
+
+                                               // Remove existing notification if already exists for code but differs in parameters.
+                                               existingNotification = setting.notifications( notification.code );
+                                               if ( existingNotification ) {
+                                                       needsReplacement = ( notification.type !== existingNotification.type ) || ! _.isEqual( notification.data, existingNotification.data );
+                                               }
+                                               if ( needsReplacement ) {
+                                                       setting.notifications.remove( code );
+                                               }
+
+                                               if ( ! setting.notifications.has( notification.code ) ) {
+                                                       setting.notifications.add( code, notification );
+                                               }
+                                               invalidSettings.push( setting.id );
+                                       } );
+                               }
+
+                               // Remove notification errors that are no longer valid.
+                               setting.notifications.each( function( notification ) {
+                                       if ( 'error' === notification.type && ( true === validity || ! validity[ notification.code ] ) ) {
+                                               setting.notifications.remove( notification.code );
+                                       }
+                               } );
+                       }
+               } );
+
+               if ( args.focusInvalidControl ) {
+                       invalidSettingControls = api.findControlsForSettings( invalidSettings );
+
+                       // Focus on the first control that is inside of an expanded section (one that is visible).
+                       _( _.values( invalidSettingControls ) ).find( function( controls ) {
+                               return _( controls ).find( function( control ) {
+                                       var isExpanded = control.section() && api.section.has( control.section() ) && api.section( control.section() ).expanded();
+                                       if ( isExpanded && control.expanded ) {
+                                               isExpanded = control.expanded();
+                                       }
+                                       if ( isExpanded ) {
+                                               control.focus();
+                                               wasFocused = true;
+                                       }
+                                       return wasFocused;
+                               } );
+                       } );
+
+                       // Focus on the first invalid control.
+                       if ( ! wasFocused && ! _.isEmpty( invalidSettingControls ) ) {
+                               _.values( invalidSettingControls )[0][0].focus();
+                       }
+               }
+       };
+
+       /**
+        * Find all controls associated with the given settings.
+        *
+        * @since 4.6.0
+        * @param {string[]} settingIds Setting IDs.
+        * @returns {object<string, wp.customize.Control>} Mapping setting ids to arrays of controls.
+        */
+       api.findControlsForSettings = function findControlsForSettings( settingIds ) {
+               var controls = {}, settingControls;
+               _.each( _.unique( settingIds ), function( settingId ) {
+                       var setting = api( settingId );
+                       if ( setting ) {
+                               settingControls = setting.findControls();
+                               if ( settingControls && settingControls.length > 0 ) {
+                                       controls[ settingId ] = settingControls;
+                               }
+                       }
+               } );
+               return controls;
+       };
+
+       /**
+        * Sort panels, sections, controls by priorities. Hide empty sections and panels.
+        *
+        * @since 4.1.0
+        */
+       api.reflowPaneContents = _.bind( function () {
+
+               var appendContainer, activeElement, rootContainers, rootNodes = [], wasReflowed = false;
+
+               if ( document.activeElement ) {
+                       activeElement = $( document.activeElement );
+               }
+
+               // Sort the sections within each panel
+               api.panel.each( function ( panel ) {
+                       var sections = panel.sections(),
+                               sectionContainers = _.pluck( sections, 'container' );
+                       rootNodes.push( panel );
+                       appendContainer = panel.container.find( 'ul:first' );
+                       if ( ! api.utils.areElementListsEqual( sectionContainers, appendContainer.children( '[id]' ) ) ) {
+                               _( sections ).each( function ( section ) {
+                                       appendContainer.append( section.container );
+                               } );
+                               wasReflowed = true;
+                       }
+               } );
+
+               // Sort the controls within each section
+               api.section.each( function ( section ) {
+                       var controls = section.controls(),
+                               controlContainers = _.pluck( controls, 'container' );
+                       if ( ! section.panel() ) {
+                               rootNodes.push( section );
+                       }
+                       appendContainer = section.container.find( 'ul:first' );
+                       if ( ! api.utils.areElementListsEqual( controlContainers, appendContainer.children( '[id]' ) ) ) {
+                               _( controls ).each( function ( control ) {
+                                       appendContainer.append( control.container );
+                               } );
+                               wasReflowed = true;
+                       }
+               } );
+
+               // Sort the root panels and sections
+               rootNodes.sort( api.utils.prioritySort );
+               rootContainers = _.pluck( rootNodes, 'container' );
+               appendContainer = $( '#customize-theme-controls' ).children( 'ul' ); // @todo This should be defined elsewhere, and to be configurable
+               if ( ! api.utils.areElementListsEqual( rootContainers, appendContainer.children() ) ) {
+                       _( rootNodes ).each( function ( rootNode ) {
+                               appendContainer.append( rootNode.container );
+                       } );
+                       wasReflowed = true;
+               }
+
+               // Now re-trigger the active Value callbacks to that the panels and sections can decide whether they can be rendered
+               api.panel.each( function ( panel ) {
+                       var value = panel.active();
+                       panel.active.callbacks.fireWith( panel.active, [ value, value ] );
+               } );
+               api.section.each( function ( section ) {
+                       var value = section.active();
+                       section.active.callbacks.fireWith( section.active, [ value, value ] );
+               } );
+
+               // Restore focus if there was a reflow and there was an active (focused) element
+               if ( wasReflowed && activeElement ) {
+                       activeElement.focus();
+               }
+               api.trigger( 'pane-contents-reflowed' );
+       }, api );
 
        $( function() {
                api.settings = window._wpCustomizeSettings;
                        return;
                }
 
-               // Redirect to the fallback preview if any incompatibilities are found.
-               if ( ! $.support.postMessage || ( ! $.support.cors && api.settings.isCrossDomain ) )
-                       return window.location = api.settings.url.fallback;
+               // Bail if any incompatibilities are found.
+               if ( ! $.support.postMessage || ( ! $.support.cors && api.settings.isCrossDomain ) ) {
+                       return;
+               }
 
                var parent, topFocus,
                        body = $( document.body ),
                        overlay = body.children( '.wp-full-overlay' ),
-                       title = $( '#customize-info .theme-name.site-title' ),
+                       title = $( '#customize-info .panel-title.site-title' ),
                        closeBtn = $( '.customize-controls-close' ),
-                       saveBtn = $( '#save' );
+                       saveBtn = $( '#save' ),
+                       footerActions = $( '#customize-footer-actions' );
 
                // Prevent the form from saving when enter is pressed on an input or select element.
                $('#customize-controls').on( 'keydown', function( e ) {
                });
 
                // Expand/Collapse the main customizer customize info.
-               $( '#customize-info' ).find( '> .accordion-section-title' ).on( 'click keydown', function( event ) {
-                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
-                               return;
-                       }
-                       event.preventDefault(); // Keep this AFTER the key filter above
-
-                       var section = $( this ).parent(),
-                               content = section.find( '.accordion-section-content:first' );
+               $( '.customize-info' ).find( '> .accordion-section-title .customize-help-toggle' ).on( 'click', function() {
+                       var section = $( this ).closest( '.accordion-section' ),
+                               content = section.find( '.customize-panel-description:first' );
 
                        if ( section.hasClass( 'cannot-expand' ) ) {
                                return;
                        if ( section.hasClass( 'open' ) ) {
                                section.toggleClass( 'open' );
                                content.slideUp( api.Panel.prototype.defaultExpandedArguments.duration );
+                               $( this ).attr( 'aria-expanded', false );
                        } else {
                                content.slideDown( api.Panel.prototype.defaultExpandedArguments.duration );
                                section.toggleClass( 'open' );
+                               $( this ).attr( 'aria-expanded', true );
                        }
                });
 
 
                        nonce: api.settings.nonce,
 
+                       /**
+                        * Build the query to send along with the Preview request.
+                        *
+                        * @return {object}
+                        */
                        query: function() {
                                var dirtyCustomized = {};
                                api.each( function ( value, key ) {
                        },
 
                        save: function() {
-                               var self  = this,
-                                       query = $.extend( this.query(), {
-                                               action: 'customize_save',
-                                               nonce:  this.nonce.save
-                                       } ),
+                               var self = this,
                                        processing = api.state( 'processing' ),
                                        submitWhenDoneProcessing,
-                                       submit;
+                                       submit,
+                                       modifiedWhileSaving = {},
+                                       invalidSettings = [],
+                                       invalidControls;
 
                                body.addClass( 'saving' );
 
+                               function captureSettingModifiedDuringSave( setting ) {
+                                       modifiedWhileSaving[ setting.id ] = true;
+                               }
+                               api.bind( 'change', captureSettingModifiedDuringSave );
+
                                submit = function () {
-                                       var request = $.post( api.settings.url.ajax, query );
+                                       var request, query;
+
+                                       /*
+                                        * Block saving if there are any settings that are marked as
+                                        * invalid from the client (not from the server). Focus on
+                                        * the control.
+                                        */
+                                       api.each( function( setting ) {
+                                               setting.notifications.each( function( notification ) {
+                                                       if ( 'error' === notification.type && ( ! notification.data || ! notification.data.from_server ) ) {
+                                                               invalidSettings.push( setting.id );
+                                                       }
+                                               } );
+                                       } );
+                                       invalidControls = api.findControlsForSettings( invalidSettings );
+                                       if ( ! _.isEmpty( invalidControls ) ) {
+                                               _.values( invalidControls )[0][0].focus();
+                                               body.removeClass( 'saving' );
+                                               api.unbind( 'change', captureSettingModifiedDuringSave );
+                                               return;
+                                       }
+
+                                       query = $.extend( self.query(), {
+                                               nonce:  self.nonce.save
+                                       } );
+                                       request = wp.ajax.post( 'customize_save', query );
+
+                                       // Disable save button during the save request.
+                                       saveBtn.prop( 'disabled', true );
 
                                        api.trigger( 'save', request );
 
                                        request.always( function () {
                                                body.removeClass( 'saving' );
+                                               saveBtn.prop( 'disabled', false );
+                                               api.unbind( 'change', captureSettingModifiedDuringSave );
                                        } );
 
-                                       request.done( function( response ) {
-                                               // Check if the user is logged out.
+                                       request.fail( function ( response ) {
                                                if ( '0' === response ) {
+                                                       response = 'not_logged_in';
+                                               } else if ( '-1' === response ) {
+                                                       // Back-compat in case any other check_ajax_referer() call is dying
+                                                       response = 'invalid_nonce';
+                                               }
+
+                                               if ( 'invalid_nonce' === response ) {
+                                                       self.cheatin();
+                                               } else if ( 'not_logged_in' === response ) {
                                                        self.preview.iframe.hide();
                                                        self.login().done( function() {
                                                                self.save();
                                                                self.preview.iframe.show();
                                                        } );
-                                                       return;
                                                }
 
-                                               // Check for cheaters.
-                                               if ( '-1' === response ) {
-                                                       self.cheatin();
-                                                       return;
+                                               if ( response.setting_validities ) {
+                                                       api._handleSettingValidities( {
+                                                               settingValidities: response.setting_validities,
+                                                               focusInvalidControl: true
+                                                       } );
                                                }
 
-                                               // Clear setting dirty states
-                                               api.each( function ( value ) {
-                                                       value._dirty = false;
+                                               api.trigger( 'error', response );
+                                       } );
+
+                                       request.done( function( response ) {
+
+                                               // Clear setting dirty states, if setting wasn't modified while saving.
+                                               api.each( function( setting ) {
+                                                       if ( ! modifiedWhileSaving[ setting.id ] ) {
+                                                               setting._dirty = false;
+                                                       }
                                                } );
-                                               api.trigger( 'saved' );
+
+                                               api.previewer.send( 'saved', response );
+
+                                               if ( response.setting_validities ) {
+                                                       api._handleSettingValidities( {
+                                                               settingValidities: response.setting_validities,
+                                                               focusInvalidControl: true
+                                                       } );
+                                               }
+
+                                               api.trigger( 'saved', response );
+
+                                               // Restore the global dirty state if any settings were modified during save.
+                                               if ( ! _.isEmpty( modifiedWhileSaving ) ) {
+                                                       api.state( 'saved' ).set( false );
+                                               }
                                        } );
                                };
 
                        $.extend( this.nonce, nonce );
                });
 
+               // Refresh the nonces if login sends updated nonces over.
+               api.bind( 'nonce-refresh', function( nonce ) {
+                       $.extend( api.settings.nonce, nonce );
+                       $.extend( api.previewer.nonce, nonce );
+                       api.previewer.send( 'nonce-refresh', nonce );
+               });
+
                // Create Settings
                $.each( api.settings.settings, function( id, data ) {
-                       api.create( id, id, data.value, {
+                       var constructor = api.settingConstructor[ data.type ] || api.Setting,
+                               setting;
+
+                       setting = new constructor( id, data.value, {
                                transport: data.transport,
-                               previewer: api.previewer
+                               previewer: api.previewer,
+                               dirty: !! data.dirty
                        } );
+                       api.add( id, setting );
                });
 
                // Create Panels
                });
 
                // Focus the autofocused element
-               _.each( [ 'panel', 'section', 'control' ], function ( type ) {
-                       var instance, id = api.settings.autofocus[ type ];
-                       if ( id && api[ type ]( id ) ) {
-                               instance = api[ type ]( id );
-                               // Wait until the element is embedded in the DOM
-                               instance.deferred.embedded.done( function () {
-                                       // Wait until the preview has activated and so active panels, sections, controls have been set
-                                       api.previewer.deferred.active.done( function () {
+               _.each( [ 'panel', 'section', 'control' ], function( type ) {
+                       var id = api.settings.autofocus[ type ];
+                       if ( ! id ) {
+                               return;
+                       }
+
+                       /*
+                        * Defer focus until:
+                        * 1. The panel, section, or control exists (especially for dynamically-created ones).
+                        * 2. The instance is embedded in the document (and so is focusable).
+                        * 3. The preview has finished loading so that the active states have been set.
+                        */
+                       api[ type ]( id, function( instance ) {
+                               instance.deferred.embedded.done( function() {
+                                       api.previewer.deferred.active.done( function() {
                                                instance.focus();
                                        });
                                });
-                       }
+                       });
                });
 
-               /**
-                * Sort panels, sections, controls by priorities. Hide empty sections and panels.
-                *
-                * @since 4.1.0
-                */
-               api.reflowPaneContents = _.bind( function () {
-
-                       var appendContainer, activeElement, rootContainers, rootNodes = [], wasReflowed = false;
-
-                       if ( document.activeElement ) {
-                               activeElement = $( document.activeElement );
-                       }
-
-                       // Sort the sections within each panel
-                       api.panel.each( function ( panel ) {
-                               var sections = panel.sections(),
-                                       sectionContainers = _.pluck( sections, 'container' );
-                               rootNodes.push( panel );
-                               appendContainer = panel.container.find( 'ul:first' );
-                               if ( ! api.utils.areElementListsEqual( sectionContainers, appendContainer.children( '[id]' ) ) ) {
-                                       _( sections ).each( function ( section ) {
-                                               appendContainer.append( section.container );
-                                       } );
-                                       wasReflowed = true;
-                               }
-                       } );
-
-                       // Sort the controls within each section
-                       api.section.each( function ( section ) {
-                               var controls = section.controls(),
-                                       controlContainers = _.pluck( controls, 'container' );
-                               if ( ! section.panel() ) {
-                                       rootNodes.push( section );
-                               }
-                               appendContainer = section.container.find( 'ul:first' );
-                               if ( ! api.utils.areElementListsEqual( controlContainers, appendContainer.children( '[id]' ) ) ) {
-                                       _( controls ).each( function ( control ) {
-                                               appendContainer.append( control.container );
-                                       } );
-                                       wasReflowed = true;
-                               }
-                       } );
-
-                       // Sort the root panels and sections
-                       rootNodes.sort( api.utils.prioritySort );
-                       rootContainers = _.pluck( rootNodes, 'container' );
-                       appendContainer = $( '#customize-theme-controls' ).children( 'ul' ); // @todo This should be defined elsewhere, and to be configurable
-                       if ( ! api.utils.areElementListsEqual( rootContainers, appendContainer.children() ) ) {
-                               _( rootNodes ).each( function ( rootNode ) {
-                                       appendContainer.append( rootNode.container );
-                               } );
-                               wasReflowed = true;
-                       }
-
-                       // Now re-trigger the active Value callbacks to that the panels and sections can decide whether they can be rendered
-                       api.panel.each( function ( panel ) {
-                               var value = panel.active();
-                               panel.active.callbacks.fireWith( panel.active, [ value, value ] );
-                       } );
-                       api.section.each( function ( section ) {
-                               var value = section.active();
-                               section.active.callbacks.fireWith( section.active, [ value, value ] );
-                       } );
-
-                       // Restore focus if there was a reflow and there was an active (focused) element
-                       if ( wasReflowed && activeElement ) {
-                               activeElement.focus();
-                       }
-               }, api );
                api.bind( 'ready', api.reflowPaneContents );
-               api.reflowPaneContents = _.debounce( api.reflowPaneContents, 100 );
                $( [ api.panel, api.section, api.control ] ).each( function ( i, values ) {
-                       values.bind( 'add', api.reflowPaneContents );
-                       values.bind( 'change', api.reflowPaneContents );
-                       values.bind( 'remove', api.reflowPaneContents );
+                       var debouncedReflowPaneContents = _.debounce( api.reflowPaneContents, 100 );
+                       values.bind( 'add', debouncedReflowPaneContents );
+                       values.bind( 'change', debouncedReflowPaneContents );
+                       values.bind( 'remove', debouncedReflowPaneContents );
                } );
 
                // Check if preview url is valid and load the preview frame.
                        });
 
                        activated.bind( function( to ) {
-                               if ( to )
+                               if ( to ) {
                                        api.trigger( 'activated' );
+                               }
                        });
 
                        // Expose states to the API.
                        event.preventDefault();
                });
 
-               // Go back to the top-level Customizer accordion.
-               $( '#customize-header-actions' ).on( 'click keydown', '.control-panel-back', function( event ) {
-                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
-                               return;
-                       }
-
-                       event.preventDefault(); // Keep this AFTER the key filter above
-                       api.panel.each( function ( panel ) {
-                               panel.collapse();
-                       });
-               });
-
                closeBtn.keydown( function( event ) {
                        if ( 9 === event.which ) // tab
                                return;
                        event.preventDefault();
                });
 
-               $('.collapse-sidebar').on( 'click keydown', function( event ) {
-                       if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
-                               return;
+               $( '.collapse-sidebar' ).on( 'click', function() {
+                       if ( 'true' === $( this ).attr( 'aria-expanded' ) ) {
+                               $( this ).attr({ 'aria-expanded': 'false', 'aria-label': api.l10n.expandSidebar });
+                       } else {
+                               $( this ).attr({ 'aria-expanded': 'true', 'aria-label': api.l10n.collapseSidebar });
                        }
 
                        overlay.toggleClass( 'collapsed' ).toggleClass( 'expanded' );
-                       event.preventDefault();
                });
 
+               // Keyboard shortcuts - esc to exit section/panel.
+               $( 'body' ).on( 'keydown', function( event ) {
+                       var collapsedObject, expandedControls = [], expandedSections = [], expandedPanels = [];
+
+                       if ( 27 !== event.which ) { // Esc.
+                               return;
+                       }
+
+                       // Check for expanded expandable controls (e.g. widgets and nav menus items), sections, and panels.
+                       api.control.each( function( control ) {
+                               if ( control.expanded && control.expanded() && _.isFunction( control.collapse ) ) {
+                                       expandedControls.push( control );
+                               }
+                       });
+                       api.section.each( function( section ) {
+                               if ( section.expanded() ) {
+                                       expandedSections.push( section );
+                               }
+                       });
+                       api.panel.each( function( panel ) {
+                               if ( panel.expanded() ) {
+                                       expandedPanels.push( panel );
+                               }
+                       });
+
+                       // Skip collapsing expanded controls if there are no expanded sections.
+                       if ( expandedControls.length > 0 && 0 === expandedSections.length ) {
+                               expandedControls.length = 0;
+                       }
+
+                       // Collapse the most granular expanded object.
+                       collapsedObject = expandedControls[0] || expandedSections[0] || expandedPanels[0];
+                       if ( collapsedObject ) {
+                               collapsedObject.collapse();
+                               event.preventDefault();
+                       }
+               });
+
+               $( '.customize-controls-preview-toggle' ).on( 'click', function() {
+                       overlay.toggleClass( 'preview-only' );
+               });
+
+               // Previewed device bindings.
+               api.previewedDevice = new api.Value();
+
+               // Set the default device.
+               api.bind( 'ready', function() {
+                       _.find( api.settings.previewableDevices, function( value, key ) {
+                               if ( true === value['default'] ) {
+                                       api.previewedDevice.set( key );
+                                       return true;
+                               }
+                       } );
+               } );
+
+               // Set the toggled device.
+               footerActions.find( '.devices button' ).on( 'click', function( event ) {
+                       api.previewedDevice.set( $( event.currentTarget ).data( 'device' ) );
+               });
+
+               // Bind device changes.
+               api.previewedDevice.bind( function( newDevice ) {
+                       var overlay = $( '.wp-full-overlay' ),
+                               devices = '';
+
+                       footerActions.find( '.devices button' )
+                               .removeClass( 'active' )
+                               .attr( 'aria-pressed', false );
+
+                       footerActions.find( '.devices .preview-' + newDevice )
+                               .addClass( 'active' )
+                               .attr( 'aria-pressed', true );
+
+                       $.each( api.settings.previewableDevices, function( device ) {
+                               devices += ' preview-' + device;
+                       } );
+
+                       overlay
+                               .removeClass( devices )
+                               .addClass( 'preview-' + newDevice );
+               } );
+
                // Bind site title display to the corresponding field.
                if ( title.length ) {
-                       $( '#customize-control-blogname input' ).on( 'input', function() {
-                               title.text( this.value );
+                       api( 'blogname', function( setting ) {
+                               var updateTitle = function() {
+                                       title.text( $.trim( setting() ) || api.l10n.untitledBlogName );
+                               };
+                               setting.bind( updateTitle );
+                               updateTitle();
                        } );
                }
 
-               // Create a potential postMessage connection with the parent frame.
+               /*
+                * Create a postMessage connection with a parent frame,
+                * in case the Customizer frame was opened with the Customize loader.
+                *
+                * @see wp.customize.Loader
+                */
                parent = new api.Messenger({
                        url: api.settings.url.parent,
                        channel: 'loader'
                });
 
-               // If we receive a 'back' event, we're inside an iframe.
-               // Send any clicks to the 'Return' link to the parent page.
+               /*
+                * If we receive a 'back' event, we're inside an iframe.
+                * Send any clicks to the 'Return' link to the parent page.
+                */
                parent.bind( 'back', function() {
                        closeBtn.on( 'click.customize-controls-close', function( event ) {
                                event.preventDefault();
                // Prompt user with AYS dialog if leaving the Customizer with unsaved changes
                $( window ).on( 'beforeunload', function () {
                        if ( ! api.state( 'saved' )() ) {
+                               setTimeout( function() {
+                                       overlay.removeClass( 'customize-loading' );
+                               }, 1 );
                                return api.l10n.saveAlert;
                        }
                } );
                        });
                } );
 
-               // When activated, let the loader handle redirecting the page.
-               // If no loader exists, redirect the page ourselves (if a url exists).
-               api.bind( 'activated', function() {
-                       if ( parent.targetWindow() )
-                               parent.send( 'activated', api.settings.url.activated );
-                       else if ( api.settings.url.activated )
-                               window.location = api.settings.url.activated;
+               // Pass titles to the parent
+               api.bind( 'title', function( newTitle ) {
+                       parent.send( 'title', newTitle );
                });
 
                // Initialize the connection with the parent frame.
                        });
                });
 
+               // Change previewed URL to the homepage when changing the page_on_front.
+               api( 'show_on_front', 'page_on_front', function( showOnFront, pageOnFront ) {
+                       var updatePreviewUrl = function() {
+                               if ( showOnFront() === 'page' && parseInt( pageOnFront(), 10 ) > 0 ) {
+                                       api.previewer.previewUrl.set( api.settings.url.home );
+                               }
+                       };
+                       showOnFront.bind( updatePreviewUrl );
+                       pageOnFront.bind( updatePreviewUrl );
+               });
+
+               // Change the previewed URL to the selected page when changing the page_for_posts.
+               api( 'page_for_posts', function( setting ) {
+                       setting.bind(function( pageId ) {
+                               pageId = parseInt( pageId, 10 );
+                               if ( pageId > 0 ) {
+                                       api.previewer.previewUrl.set( api.settings.url.home + '?page_id=' + pageId );
+                               }
+                       });
+               });
+
+               // Update the setting validities.
+               api.previewer.bind( 'selective-refresh-setting-validities', function handleSelectiveRefreshedSettingValidities( settingValidities ) {
+                       api._handleSettingValidities( {
+                               settingValidities: settingValidities,
+                               focusInvalidControl: false
+                       } );
+               } );
+
+               // Focus on the control that is associated with the given setting.
+               api.previewer.bind( 'focus-control-for-setting', function( settingId ) {
+                       var matchedControl;
+                       api.control.each( function( control ) {
+                               var settingIds = _.pluck( control.settings, 'id' );
+                               if ( -1 !== _.indexOf( settingIds, settingId ) ) {
+                                       matchedControl = control;
+                               }
+                       } );
+
+                       if ( matchedControl ) {
+                               matchedControl.focus();
+                       }
+               } );
+
+               // Refresh the preview when it requests.
+               api.previewer.bind( 'refresh', function() {
+                       api.previewer.refresh();
+               });
+
                api.trigger( 'ready' );
 
                // Make sure left column gets focus