diff --git a/src/js/_enqueues/wp/customize/base.js b/src/js/_enqueues/wp/customize/base.js
index 4afaa945571f0..b4a380efdd9ab 100644
--- a/src/js/_enqueues/wp/customize/base.js
+++ b/src/js/_enqueues/wp/customize/base.js
@@ -5,9 +5,12 @@
 /** @namespace wp */
 window.wp = window.wp || {};
 
-(function( exports, $ ){
-	var api = {}, ctor, inherits,
-		slice = Array.prototype.slice;
+/**
+ * @param {Object}       wp The WordPress global object.
+ * @param {JQueryStatic} $  The jQuery object.
+ */
+(function( wp, $ ){
+	var api = {}, ctor, inherits;
 
 	// Shared empty constructor function to aid in prototype-chain creation.
 	ctor = function() {};
@@ -17,10 +20,10 @@ window.wp = window.wp || {};
 	 * Similar to `goog.inherits`, but uses a hash of prototype properties and
 	 * class properties to be extended.
 	 *
-	 * @param object parent      Parent class constructor to inherit from.
-	 * @param object protoProps  Properties to apply to the prototype for use as class instance properties.
-	 * @param object staticProps Properties to apply directly to the class constructor.
-	 * @return child The subclassed constructor.
+	 * @param {Object} parent        Parent class constructor to inherit from.
+	 * @param {Object} [protoProps]  Properties to apply to the prototype for use as class instance properties.
+	 * @param {Object} [staticProps] Properties to apply directly to the class constructor.
+	 * @return {Function} The subclassed constructor.
 	 */
 	inherits = function( parent, protoProps, staticProps ) {
 		var child;
@@ -33,14 +36,14 @@ window.wp = window.wp || {};
 		if ( protoProps && protoProps.hasOwnProperty( 'constructor' ) ) {
 			child = protoProps.constructor;
 		} else {
-			child = function() {
+			child = function( ...args ) {
 				/*
 				 * Storing the result `super()` before returning the value
 				 * prevents a bug in Opera where, if the constructor returns
 				 * a function, Opera will reject the return value in favor of
 				 * the original object. This causes all sorts of trouble.
 				 */
-				var result = parent.apply( this, arguments );
+				var result = parent.apply( this, args );
 				return result;
 			};
 		}
@@ -75,13 +78,28 @@ window.wp = window.wp || {};
 
 	/**
 	 * Base class for object inheritance.
+	 *
+	 * The arguments are normally passed straight through to the class's
+	 * initialize method. As a special case, when the first argument is
+	 * api.Class.applicator, the second argument is used as the array of
+	 * arguments for initialize and the third is used to extend the instance.
+	 * This allows a class to be constructed from an argument list that is only
+	 * known at runtime. See {@link wp.customize.Values#create}.
+	 *
+	 * @param {...*} args Arguments for the class's initialize method. Or
+	 *                    api.Class.applicator, followed by the array of
+	 *                    arguments for the initialize method, followed by an
+	 *                    optional object of properties to extend the instance
+	 *                    with.
+	 * @return {Object|Function} The instance of the class, which is a function when the class
+	 *                           defines an instance method, so that the instance is callable.
 	 */
-	api.Class = function( applicator, argsArray, options ) {
-		var magic, args = arguments;
+	api.Class = function( ...args ) {
+		var magic;
 
-		if ( applicator && argsArray && api.Class.applicator === applicator ) {
-			args = argsArray;
-			$.extend( this, options || {} );
+		if ( args[0] && args[1] && api.Class.applicator === args[0] ) {
+			$.extend( this, args[2] || {} );
+			args = args[1];
 		}
 
 		magic = this;
@@ -94,8 +112,8 @@ window.wp = window.wp || {};
 		 * It is also an object that has properties and methods inside it.
 		 */
 		if ( this.instance ) {
-			magic = function() {
-				return magic.instance.apply( magic, arguments );
+			magic = function( ...instanceArgs ) {
+				return magic.instance.apply( magic, instanceArgs );
 			};
 
 			$.extend( magic, this );
@@ -108,9 +126,9 @@ window.wp = window.wp || {};
 	/**
 	 * Creates a subclass of the class.
 	 *
-	 * @param object protoProps  Properties to apply to the prototype.
-	 * @param object staticProps Properties to apply directly to the class.
-	 * @return child The subclass.
+	 * @param {Object} [protoProps]  Properties to apply to the prototype.
+	 * @param {Object} [staticProps] Properties to apply directly to the class.
+	 * @return {Function} The subclass.
 	 */
 	api.Class.extend = function( protoProps, staticProps ) {
 		var child = inherits( this, protoProps, staticProps );
@@ -155,23 +173,44 @@ window.wp = window.wp || {};
 	 * Used as a mixin.
 	 */
 	api.Events = {
-		trigger: function( id ) {
+		/**
+		 * Trigger an event, invoking all of the callbacks bound to it.
+		 *
+		 * @param {string} id      ID of the event to trigger.
+		 * @param {...*}   [args]  Zero or more arguments to pass to the bound callbacks.
+		 * @return {Object} The instance the mixin is applied to.
+		 */
+		trigger: function( id, ...args ) {
 			if ( this.topics && this.topics[ id ] ) {
-				this.topics[ id ].fireWith( this, slice.call( arguments, 1 ) );
+				this.topics[ id ].fireWith( this, args );
 			}
 			return this;
 		},
 
-		bind: function( id ) {
+		/**
+		 * Bind one or more callbacks to an event.
+		 *
+		 * @param {string}      id        ID of the event to bind to.
+		 * @param {...Function} callbacks A function, or multiple functions, to add to the callback stack.
+		 * @return {Object} The instance the mixin is applied to.
+		 */
+		bind: function( id, ...callbacks ) {
 			this.topics = this.topics || {};
 			this.topics[ id ] = this.topics[ id ] || $.Callbacks();
-			this.topics[ id ].add.apply( this.topics[ id ], slice.call( arguments, 1 ) );
+			this.topics[ id ].add.apply( this.topics[ id ], callbacks );
 			return this;
 		},
 
-		unbind: function( id ) {
+		/**
+		 * Unbind one or more previously bound callbacks from an event.
+		 *
+		 * @param {string}      id        ID of the event to unbind from.
+		 * @param {...Function} callbacks A function, or multiple functions, to remove from the callback stack.
+		 * @return {Object} The instance the mixin is applied to.
+		 */
+		unbind: function( id, ...callbacks ) {
 			if ( this.topics && this.topics[ id ] ) {
-				this.topics[ id ].remove.apply( this.topics[ id ], slice.call( arguments, 1 ) );
+				this.topics[ id ].remove.apply( this.topics[ id ], callbacks );
 			}
 			return this;
 		}
@@ -183,11 +222,11 @@ window.wp = window.wp || {};
 	 * @memberOf wp.customize
 	 * @alias wp.customize.Value
 	 *
-	 * @constructor
+	 * @class
 	 */
 	api.Value = api.Class.extend(/** @lends wp.customize.Value.prototype */{
 		/**
-		 * @param {mixed}  initial The initial value.
+		 * @param {*}      initial The initial value.
 		 * @param {Object} options
 		 */
 		initialize: function( initial, options ) {
@@ -204,14 +243,14 @@ window.wp = window.wp || {};
 		 * Magic. Returns a function that will become the instance.
 		 * Set to null to prevent the instance from extending a function.
 		 */
-		instance: function() {
-			return arguments.length ? this.set.apply( this, arguments ) : this.get();
+		instance: function( ...args ) {
+			return args.length ? this.set.apply( this, args ) : this.get();
 		},
 
 		/**
 		 * Get the value.
 		 *
-		 * @return {mixed}
+		 * @return {*} The value.
 		 */
 		get: function() {
 			return this._value;
@@ -220,12 +259,14 @@ window.wp = window.wp || {};
 		/**
 		 * Set the value and trigger all bound callbacks.
 		 *
-		 * @param {Object} to New value.
+		 * @param {*}      to     New value.
+		 * @param {...*}   [args] Zero or more additional arguments to pass to the setter.
+		 * @return {wp.customize.Value} The instance of the Value.
 		 */
-		set: function( to ) {
+		set: function( to, ...args ) {
 			var from = this._value;
 
-			to = this._setter.apply( this, arguments );
+			to = this._setter( to, ...args );
 			to = this.validate( to );
 
 			// Bail if the sanitized value is null or unchanged.
@@ -267,51 +308,81 @@ window.wp = window.wp || {};
 		/**
 		 * Bind a function to be invoked whenever the value changes.
 		 *
-		 * @param {...Function} A function, or multiple functions, to add to the callback stack.
+		 * @param {...Function} callbacks A function, or multiple functions, to add to the callback stack.
+		 * @return {wp.customize.Value} The instance of the Value.
 		 */
-		bind: function() {
-			this.callbacks.add.apply( this.callbacks, arguments );
+		bind: function( ...callbacks ) {
+			this.callbacks.add.apply( this.callbacks, callbacks );
 			return this;
 		},
 
 		/**
 		 * Unbind a previously bound function.
 		 *
-		 * @param {...Function} A function, or multiple functions, to remove from the callback stack.
+		 * @param {...Function} callbacks A function, or multiple functions, to remove from the callback stack.
+		 * @return {wp.customize.Value} The instance of the Value.
 		 */
-		unbind: function() {
-			this.callbacks.remove.apply( this.callbacks, arguments );
+		unbind: function( ...callbacks ) {
+			this.callbacks.remove.apply( this.callbacks, callbacks );
 			return this;
 		},
 
-		link: function() { // values*
+		/**
+		 * Update this value whenever one or more other values change.
+		 *
+		 * Note that this is one-directional: this value follows the supplied
+		 * values, not the other way around. Use sync() to link in both
+		 * directions.
+		 *
+		 * @param {...wp.customize.Value} values A value, or multiple values, for this value to follow.
+		 * @return {wp.customize.Value} The instance of the Value.
+		 */
+		link: function( ...values ) {
 			var set = this.set;
-			$.each( arguments, function() {
+			$.each( values, function() {
 				this.bind( set );
 			});
 			return this;
 		},
 
-		unlink: function() { // values*
+		/**
+		 * Stop updating this value when one or more other values change.
+		 *
+		 * @param {...wp.customize.Value} values A value, or multiple values, for this value to stop following.
+		 * @return {wp.customize.Value} The instance of the Value.
+		 */
+		unlink: function( ...values ) {
 			var set = this.set;
-			$.each( arguments, function() {
+			$.each( values, function() {
 				this.unbind( set );
 			});
 			return this;
 		},
 
-		sync: function() { // values*
+		/**
+		 * Link this value with one or more other values in both directions.
+		 *
+		 * @param {...wp.customize.Value} values A value, or multiple values, to keep in sync with this value.
+		 * @return {wp.customize.Value} The instance of the Value.
+		 */
+		sync: function( ...values ) {
 			var that = this;
-			$.each( arguments, function() {
+			$.each( values, function() {
 				that.link( this );
 				this.link( that );
 			});
 			return this;
 		},
 
-		unsync: function() { // values*
+		/**
+		 * Stop keeping this value in sync with one or more other values.
+		 *
+		 * @param {...wp.customize.Value} values A value, or multiple values, to stop keeping in sync with this value.
+		 * @return {wp.customize.Value} The instance of the Value.
+		 */
+		unsync: function( ...values ) {
 			var that = this;
-			$.each( arguments, function() {
+			$.each( values, function() {
 				that.unlink( this );
 				this.unlink( that );
 			});
@@ -325,7 +396,7 @@ window.wp = window.wp || {};
 	 * @memberOf wp.customize
 	 * @alias wp.customize.Values
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.customize.Class
 	 * @mixes wp.customize.Events
 	 */
@@ -334,7 +405,7 @@ window.wp = window.wp || {};
 		/**
 		 * The default constructor for items of the collection.
 		 *
-		 * @type {object}
+		 * @type {Function}
 		 */
 		defaultConstructor: api.Value,
 
@@ -352,27 +423,27 @@ window.wp = window.wp || {};
 		 * the last to be a function callback that will be invoked when the requested
 		 * items are available.
 		 *
-		 * @see {api.Values.when}
+		 * @see {@link wp.customize.Values#when}
 		 *
-		 * @param {string} id ID of the item.
-		 * @param {...}       Zero or more IDs of items to wait for and a callback
-		 *                    function to invoke when they're available. Optional.
-		 * @return {mixed} The item instance if only one ID was supplied.
-		 *                 A Deferred Promise object if a callback function is supplied.
+		 * @param {string}               id     ID of the item.
+		 * @param {...(string|Function)} [args] Zero or more IDs of items to wait for and a callback
+		 *                                      function to invoke when they're available. Optional.
+		 * @return {*} The item instance if only one ID was supplied.
+		 *             A Deferred Promise object if a callback function is supplied.
 		 */
-		instance: function( id ) {
-			if ( arguments.length === 1 ) {
+		instance: function( id, ...args ) {
+			if ( 0 === args.length ) {
 				return this.value( id );
 			}
 
-			return this.when.apply( this, arguments );
+			return this.when( id, ...args );
 		},
 
 		/**
 		 * Get the instance of an item.
 		 *
 		 * @param {string} id The ID of the item.
-		 * @return {[type]} [description]
+		 * @return {*} The item instance.
 		 */
 		value: function( id ) {
 			return this._value[ id ];
@@ -382,7 +453,7 @@ window.wp = window.wp || {};
 		 * Whether the collection has an item with the given ID.
 		 *
 		 * @param {string} id The ID of the item to look for.
-		 * @return {boolean}
+		 * @return {boolean} True if the collection has an item with the given ID, false otherwise.
 		 */
 		has: function( id ) {
 			return typeof this._value[ id ] !== 'undefined';
@@ -391,9 +462,9 @@ window.wp = window.wp || {};
 		/**
 		 * Add an item to the collection.
 		 *
-		 * @param {string|wp.customize.Class} item         - The item instance to add, or the ID for the instance to add.
-		 *                                                   When an ID string is supplied, then itemObject must be provided.
-		 * @param {wp.customize.Class}        [itemObject] - The item instance when the first argument is an ID string.
+		 * @param {string|wp.customize.Class} item         The item instance to add, or the ID for the instance to add.
+		 *                                                 When an ID string is supplied, then itemObject must be provided.
+		 * @param {wp.customize.Class}        [itemObject] The item instance when the first argument is an ID string.
 		 * @return {wp.customize.Class} The new item's instance, or an existing instance if already added.
 		 */
 		add: function( item, itemObject ) {
@@ -436,19 +507,19 @@ window.wp = window.wp || {};
 		 * Create a new item of the collection using the collection's default constructor
 		 * and store it in the collection.
 		 *
-		 * @param {string} id    The ID of the item.
-		 * @param {mixed}  value Any extra arguments are passed into the item's initialize method.
-		 * @return {mixed} The new item's instance.
+		 * @param {string} id     The ID of the item.
+		 * @param {...*}   [args] Zero or more extra arguments to pass into the item's initialize method.
+		 * @return {wp.customize.Class} The new item's instance.
 		 */
-		create: function( id ) {
-			return this.add( id, new this.defaultConstructor( api.Class.applicator, slice.call( arguments, 1 ) ) );
+		create: function( id, ...args ) {
+			return this.add( id, new this.defaultConstructor( api.Class.applicator, args ) );
 		},
 
 		/**
 		 * Iterate over all items in the collection invoking the provided callback.
 		 *
-		 * @param {Function} callback Function to invoke.
-		 * @param {Object}   context  Object context to invoke the function with. Optional.
+		 * @param {Function} callback  Function to invoke.
+		 * @param {Object}   [context] Object context to invoke the function with.
 		 */
 		each: function( callback, context ) {
 			context = typeof context === 'undefined' ? this : context;
@@ -494,11 +565,12 @@ window.wp = window.wp || {};
 		 * For example:
 		 *     when( id1, id2, id3, function( value1, value2, value3 ) {} );
 		 *
-		 * @return $.Deferred.promise();
+		 * @param {...(string|Function)} ids Zero or more IDs of items to wait for, optionally followed by
+		 *                                  a callback function to invoke once they are all available.
+		 * @return {JQuery.Promise<*>} A promise that is resolved when all of the requested values exist.
 		 */
-		when: function() {
+		when: function( ...ids ) {
 			var self = this,
-				ids  = slice.call( arguments ),
 				dfd  = $.Deferred();
 
 			// If the last argument is a callback, bind it to .done().
@@ -555,9 +627,10 @@ window.wp = window.wp || {};
 
 
 	/**
-	 * Cast a string to a jQuery collection if it isn't already.
+	 * Cast a string to a jQuery object if it isn't already.
 	 *
-	 * @param {string|jQuery collection} element
+	 * @param {string|jQuery} element A selector or an existing jQuery collection.
+	 * @return {jQuery} The jQuery collection.
 	 */
 	api.ensure = function( element ) {
 		return typeof element === 'string' ? $( element ) : element;
@@ -571,7 +644,7 @@ window.wp = window.wp || {};
 	 * @memberOf wp.customize
 	 * @alias wp.customize.Element
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.customize.Value
 	 * @augments wp.customize.Class
 	 */
@@ -600,9 +673,9 @@ window.wp = window.wp || {};
 			update = this.update;
 			refresh = this.refresh;
 
-			this.update = function( to ) {
+			this.update = function( to, ...args ) {
 				if ( to !== refresh.call( self ) ) {
-					update.apply( this, arguments );
+					update.call( this, to, ...args );
 				}
 			};
 			this.refresh = function() {
@@ -663,7 +736,7 @@ window.wp = window.wp || {};
 	 * @memberOf wp.customize
 	 * @alias wp.customize.Messenger
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.customize.Class
 	 * @mixes wp.customize.Events
 	 */
@@ -671,10 +744,10 @@ window.wp = window.wp || {};
 		/**
 		 * Create a new Value.
 		 *
-		 * @param {string} key     Unique identifier.
-		 * @param {mixed}  initial Initial value.
-		 * @param {mixed}  options Options hash. Optional.
-		 * @return {Value} Class instance of the Value.
+		 * @param {string} key       Unique identifier.
+		 * @param {*}      initial   Initial value.
+		 * @param {*}      [options] Options hash.
+		 * @return {wp.customize.Value} Class instance of the Value.
 		 */
 		add: function( key, initial, options ) {
 			return this[ key ] = new api.Value( initial, options );
@@ -683,11 +756,11 @@ window.wp = window.wp || {};
 		/**
 		 * Initialize Messenger.
 		 *
-		 * @param {Object} params  - Parameters to configure the messenger.
-		 *        {string} params.url          - The URL to communicate with.
-		 *        {window} params.targetWindow - The window instance to communicate with. Default window.parent.
-		 *        {string} params.channel      - If provided, will send the channel with each message and only accept messages a matching channel.
-		 * @param {Object} options - Extend any instance parameter or method with this object.
+		 * @param {Object} params              Parameters to configure the messenger.
+		 * @param {string} params.url          The URL to communicate with.
+		 * @param {Window} params.targetWindow The window instance to communicate with. Default window.parent.
+		 * @param {string} [params.channel]    If provided, will send the channel with each message and only accept messages a matching channel.
+		 * @param {Object} options             Extend any instance parameter or method with this object.
 		 */
 		initialize: function( params, options ) {
 			// Target the parent frame by default, but only if a parent frame exists.
@@ -707,10 +780,10 @@ window.wp = window.wp || {};
 			// First add with no value.
 			this.add( 'targetWindow', null );
 			// This avoids SecurityErrors when setting a window object in x-origin iframe'd scenarios.
-			this.targetWindow.set = function( to ) {
+			this.targetWindow.set = function( to, ...args ) {
 				var from = this._value;
 
-				to = this._setter.apply( this, arguments );
+				to = this._setter( to, ...args );
 				to = this.validate( to );
 
 				if ( null === to || from === to ) {
@@ -748,7 +821,7 @@ window.wp = window.wp || {};
 		/**
 		 * Receive data from the other window.
 		 *
-		 * @param {jQuery.Event} event Event with embedded data.
+		 * @param {JQuery.Event} event Event with embedded data.
 		 */
 		receive: function( event ) {
 			var message;
@@ -787,8 +860,8 @@ window.wp = window.wp || {};
 		/**
 		 * Send data to the other window.
 		 *
-		 * @param {string} id   The event name.
-		 * @param {Object} data Data.
+		 * @param {string} id     The event name.
+		 * @param {*}      [data] Data.
 		 */
 		send: function( id, data ) {
 			var message;
@@ -821,13 +894,13 @@ window.wp = window.wp || {};
 	 * @memberOf wp.customize
 	 * @alias wp.customize.Notification
 	 *
-	 * @param {string}  code - The error code.
-	 * @param {object}  params - Params.
-	 * @param {string}  params.message=null - The error message.
-	 * @param {string}  [params.type=error] - The notification type.
-	 * @param {boolean} [params.fromServer=false] - Whether the notification was server-sent.
-	 * @param {string}  [params.setting=null] - The setting ID that the notification is related to.
-	 * @param {*}       [params.data=null] - Any additional data.
+	 * @param {string}  code                      The error code.
+	 * @param {Object}  params                    Params.
+	 * @param {string}  [params.message=null]     The error message.
+	 * @param {string}  [params.type=error]       The notification type.
+	 * @param {boolean} [params.fromServer=false] Whether the notification was server-sent.
+	 * @param {string}  [params.setting=null]     The setting ID that the notification is related to.
+	 * @param {*}       [params.data=null]        Any additional data.
 	 */
 	api.Notification = api.Class.extend(/** @lends wp.customize.Notification.prototype */{
 
@@ -837,7 +910,7 @@ window.wp = window.wp || {};
 		 * This will be populated with template option or else it will be populated with template from the ID.
 		 *
 		 * @since 4.9.0
-		 * @var {Function}
+		 * @member {Function}
 		 */
 		template: null,
 
@@ -845,7 +918,7 @@ window.wp = window.wp || {};
 		 * ID for the template to render the notification.
 		 *
 		 * @since 4.9.0
-		 * @var {string}
+		 * @member {string}
 		 */
 		templateId: 'customize-notification',
 
@@ -853,7 +926,7 @@ window.wp = window.wp || {};
 		 * Additional class names to add to the notification container.
 		 *
 		 * @since 4.9.0
-		 * @var {string}
+		 * @member {string}
 		 */
 		containerClasses: '',
 
@@ -862,15 +935,15 @@ window.wp = window.wp || {};
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string}   code - Notification code.
-		 * @param {Object}   params - Notification parameters.
-		 * @param {string}   params.message - Message.
-		 * @param {string}   [params.type=error] - Type.
-		 * @param {string}   [params.setting] - Related setting ID.
-		 * @param {Function} [params.template] - Function for rendering template. If not provided, this will come from templateId.
-		 * @param {string}   [params.templateId] - ID for template to render the notification.
-		 * @param {string}   [params.containerClasses] - Additional class names to add to the notification container.
-		 * @param {boolean}  [params.dismissible] - Whether the notification can be dismissed.
+		 * @param {string}   code                      Notification code.
+		 * @param {Object}   params                    Notification parameters.
+		 * @param {string}   params.message            Message.
+		 * @param {string}   [params.type=error]       Type.
+		 * @param {string}   [params.setting]          Related setting ID.
+		 * @param {Function} [params.template]         Function for rendering template. If not provided, this will come from templateId.
+		 * @param {string}   [params.templateId]       ID for template to render the notification.
+		 * @param {string}   [params.containerClasses] Additional class names to add to the notification container.
+		 * @param {boolean}  [params.dismissible]      Whether the notification can be dismissed.
 		 */
 		initialize: function( code, params ) {
 			var _params;
@@ -935,7 +1008,7 @@ window.wp = window.wp || {};
 	 *
 	 * @alias wp.customize.get
 	 *
-	 * @return {Object}
+	 * @return {Object} All customize settings.
 	 */
 	api.get = function() {
 		var result = {};
@@ -990,5 +1063,5 @@ window.wp = window.wp || {};
 	 *
 	 * @namespace wp.customize
 	 */
-	exports.customize = api;
+	wp.customize = api;
 })( wp, jQuery );
diff --git a/src/js/_enqueues/wp/customize/controls.js b/src/js/_enqueues/wp/customize/controls.js
index 00123f9141c30..7b8741a32cac8 100644
--- a/src/js/_enqueues/wp/customize/controls.js
+++ b/src/js/_enqueues/wp/customize/controls.js
@@ -3,7 +3,12 @@
  */
 
 /* global _wpCustomizeHeader, _wpCustomizeBackground, _wpMediaViewsL10n, MediaElementPlayer, console, confirm */
-(function( exports, $ ){
+
+/**
+ * @param {Object}       wp The WordPress global object.
+ * @param {JQueryStatic} $  The jQuery object.
+ */
+(function( wp, $ ){
 	var Container, focus, normalizedTransitionendEventName, api = wp.customize;
 
 	var reducedMotionMediaQuery = window.matchMedia( '(prefers-reduced-motion: reduce)' );
@@ -18,7 +23,7 @@
 		 * Whether the notification should show a loading spinner.
 		 *
 		 * @since 4.9.0
-		 * @var {boolean}
+		 * @member {boolean}
 		 */
 		loading: false,
 
@@ -30,8 +35,8 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string} code - Code.
-		 * @param {Object} params - Params.
+		 * @param {string} code   Notification code.
+		 * @param {Object} params Notification params.
 		 */
 		initialize: function( code, params ) {
 			var notification = this;
@@ -60,7 +65,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {jQuery.Event} event - Event.
+		 * @param {JQuery.Event} event Event.
 		 * @return {void}
 		 */
 		handleEscape: function( event ) {
@@ -88,7 +93,7 @@
 		 * The default constructor for items of the collection.
 		 *
 		 * @since 4.9.0
-		 * @type {object}
+		 * @type {Function}
 		 */
 		defaultConstructor: api.Notification,
 
@@ -100,9 +105,9 @@
 		 * @constructs wp.customize.Notifications
 		 * @augments   wp.customize.Values
 		 *
-		 * @param {Object}  options - Options.
-		 * @param {jQuery}  [options.container] - Container element for notifications. This can be injected later.
-		 * @param {boolean} [options.alt] - Whether alternative style should be used when rendering notifications.
+		 * @param {Object}  options             Options.
+		 * @param {jQuery}  [options.container] Container element for notifications. This can be injected later.
+		 * @param {boolean} [options.alt]       Whether alternative style should be used when rendering notifications.
 		 *
 		 * @return {void}
 		 */
@@ -141,8 +146,8 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string|wp.customize.Notification} notification - Notification object to add. Alternatively code may be supplied, and in that case the second notificationObject argument must be supplied.
-		 * @param {wp.customize.Notification} [notificationObject] - Notification to add when first argument is the code string.
+		 * @param {string|wp.customize.Notification} notification  Notification object to add. Alternatively code may be supplied, and in that case the second notificationObject argument must be supplied.
+		 * @param {wp.customize.Notification} [notificationObject] Notification to add when first argument is the code string.
 		 * @return {wp.customize.Notification} Added notification (or existing instance if it was already added).
 		 */
 		add: function( notification, notificationObject ) {
@@ -165,8 +170,8 @@
 		 * Add notification to the collection.
 		 *
 		 * @since 4.9.0
-		 * @param {string} code - Notification code to remove.
-		 * @return {api.Notification} Added instance (or existing instance if it was already added).
+		 * @param {string} code Notification code to remove.
+		 * @return {wp.customize.Notification} Added instance (or existing instance if it was already added).
 		 */
 		remove: function( code ) {
 			var collection = this;
@@ -180,9 +185,9 @@
 		 * Notifications may be sorted by type followed by added time.
 		 *
 		 * @since 4.9.0
-		 * @param {Object}  args - Args.
-		 * @param {boolean} [args.sort=false] - Whether to return the notifications sorted.
-		 * @return {Array.<wp.customize.Notification>} Notifications.
+		 * @param {Object}  args              Args.
+		 * @param {boolean} [args.sort=false] Whether to return the notifications sorted.
+		 * @return {wp.customize.Notification[]} Notifications.
 		 */
 		get: function( args ) {
 			var collection = this, notifications, errorTypePriorities, params;
@@ -309,7 +314,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {jQuery.Event} event - Event.
+		 * @param {JQuery.Event} event Event.
 		 * @return {void}
 		 */
 		constrainFocus: function constrainFocus( event ) {
@@ -346,7 +351,7 @@
 		 * Default params.
 		 *
 		 * @since 4.9.0
-		 * @var {object}
+		 * @member {Object}
 		 */
 		defaults: {
 			transport: 'refresh',
@@ -366,12 +371,12 @@
 		 *
 		 * @since 3.4.0
 		 *
-		 * @param {string}  id                          - The setting ID.
-		 * @param {*}       value                       - The initial value of the setting.
-		 * @param {Object}  [options={}]                - Options.
-		 * @param {string}  [options.transport=refresh] - The transport to use for previewing. Supports 'refresh' and 'postMessage'.
-		 * @param {boolean} [options.dirty=false]       - Whether the setting should be considered initially dirty.
-		 * @param {Object}  [options.previewer]         - The Previewer instance to sync with. Defaults to wp.customize.previewer.
+		 * @param {string}  id                          The setting ID.
+		 * @param {*}       value                       The initial value of the setting.
+		 * @param {Object}  [options={}]                Options.
+		 * @param {string}  [options.transport=refresh] The transport to use for previewing. Supports 'refresh' and 'postMessage'.
+		 * @param {boolean} [options.dirty=false]       Whether the setting should be considered initially dirty.
+		 * @param {Object}  [options.previewer]         The Previewer instance to sync with. Defaults to wp.customize.previewer.
 		 */
 		initialize: function( id, value, options ) {
 			var setting = this, params;
@@ -468,7 +473,7 @@
 	 * @alias wp.customize._latestSettingRevisions
 	 *
 	 * @since 4.7.0
-	 * @type {object}
+	 * @type {Object}
 	 * @protected
 	 */
 	api._latestSettingRevisions = {};
@@ -534,14 +539,14 @@
 	 * @since 4.7.0
 	 * @access public
 	 *
-	 * @param {Object}  [changes] - Mapping of setting IDs to setting params each normally including a value property, or mapping to null.
-	 *                             If not provided, then the changes will still be obtained from unsaved dirty settings.
-	 * @param {Object}  [args] - Additional options for the save request.
-	 * @param {boolean} [args.autosave=false] - Whether changes will be stored in autosave revision if the changeset has been promoted from an auto-draft.
-	 * @param {boolean} [args.force=false] - Send request to update even when there are no changes to submit. This can be used to request the latest status of the changeset on the server.
-	 * @param {string}  [args.title] - Title to update in the changeset. Optional.
-	 * @param {string}  [args.date] - Date to update in the changeset. Optional.
-	 * @return {jQuery.Promise} Promise resolving with the response data.
+	 * @param {Object}  [changes]             Mapping of setting IDs to setting params each normally including a value property, or mapping to null.
+	 *                                        If not provided, then the changes will still be obtained from unsaved dirty settings.
+	 * @param {Object}  [args]                Additional options for the save request.
+	 * @param {boolean} [args.autosave=false] Whether changes will be stored in autosave revision if the changeset has been promoted from an auto-draft.
+	 * @param {boolean} [args.force=false]    Send request to update even when there are no changes to submit. This can be used to request the latest status of the changeset on the server.
+	 * @param {string}  [args.title]          Title to update in the changeset. Optional.
+	 * @param {string}  [args.date]           Date to update in the changeset. Optional.
+	 * @return {JQuery.Promise<*>} Promise resolving with the response data.
 	 */
 	api.requestChangesetUpdate = function requestChangesetUpdate( changes, args ) {
 		var deferred, request, submittedChanges = {}, data, submittedArgs;
@@ -672,7 +677,7 @@
 	 * @since 4.1.0
 	 *
 	 * @param {wp.customize.Class} instance
-	 * @param {Array}              properties  The names of the Value instances to watch.
+	 * @param {string[]}           properties The names of the Value instances to watch.
 	 */
 	api.utils.bubbleChildValueChanges = function ( instance, properties ) {
 		$.each( properties, function ( i, key ) {
@@ -754,7 +759,7 @@
 	 *
 	 * @param {(wp.customize.Panel|wp.customize.Section|wp.customize.Control)} a
 	 * @param {(wp.customize.Panel|wp.customize.Section|wp.customize.Control)} b
-	 * @return {number}
+	 * @return {number} A negative number if a has lower priority than b, a positive number if a has higher priority than b, or zero if they have the same priority.
 	 */
 	api.utils.prioritySort = function ( a, b ) {
 		if ( a.priority() === b.priority() && typeof a.params.instanceNumber === 'number' && typeof b.params.instanceNumber === 'number' ) {
@@ -771,8 +776,8 @@
 	 *
 	 * @since 4.1.0
 	 *
-	 * @param {jQuery.Event} event
-	 * @return {boolean}
+	 * @param {JQuery.Event} event Event object.
+	 * @return {boolean} True if the event is a keydown event but not the Enter key, false otherwise.
 	 */
 	api.utils.isKeydownButNotEnterEvent = function ( event ) {
 		return ( 'keydown' === event.type && 13 !== event.which );
@@ -785,9 +790,9 @@
 	 *
 	 * @since 4.1.0
 	 *
-	 * @param {Array|jQuery} listA
-	 * @param {Array|jQuery} listB
-	 * @return {boolean}
+	 * @param {jQuery[]|jQuery} listA First list of elements.
+	 * @param {jQuery[]|jQuery} listB Second list of elements.
+	 * @return {boolean} True if the two lists are equal, false otherwise.
 	 */
 	api.utils.areElementListsEqual = function ( listA, listB ) {
 		var equal = (
@@ -813,14 +818,14 @@
 	 *
 	 * @since 4.9.0
 	 *
-	 * @param {jQuery} button - The element to highlight.
-	 * @param {Object} [options] - Options.
-	 * @param {number} [options.delay=0] - Delay in milliseconds.
-	 * @param {jQuery} [options.focusTarget] - A target for user focus that defaults to the highlighted element.
-	 *                                         If the user focuses the target before the delay passes, the reminder
-	 *                                         is canceled. This option exists to accommodate compound buttons
-	 *                                         containing auxiliary UI, such as the Publish button augmented with a
-	 *                                         Settings button.
+	 * @param {jQuery} button                The element to highlight.
+	 * @param {Object} [options]             Options.
+	 * @param {number} [options.delay=0]     Delay in milliseconds.
+	 * @param {jQuery} [options.focusTarget] A target for user focus that defaults to the highlighted element.
+	 *                                       If the user focuses the target before the delay passes, the reminder
+	 *                                       is canceled. This option exists to accommodate compound buttons
+	 *                                       containing auxiliary UI, such as the Publish button augmented with a
+	 *                                       Settings button.
 	 * @return {Function} An idempotent function that cancels the reminder.
 	 */
 	api.utils.highlightButton = function highlightButton( button, options ) {
@@ -887,8 +892,8 @@
 	 *
 	 * @since 4.9.0
 	 *
-	 * @param {string|number|Date} datetime - Date time or timestamp of the future date.
-	 * @return {number} remainingTime - Remaining time in milliseconds.
+	 * @param {string|number|Date} datetime Date time or timestamp of the future date.
+	 * @return {number} Remaining time in milliseconds.
 	 */
 	api.utils.getRemainingTime = function getRemainingTime( datetime ) {
 		var millisecondsDivider = 1000, remainingTime, timestamp;
@@ -957,16 +962,16 @@
 		 *
 		 * @borrows wp.customize~focus as focus
 		 *
-		 * @param {string}  id - The ID for the container.
-		 * @param {Object}  options - Object containing one property: params.
-		 * @param {string}  options.title - Title shown when panel is collapsed and expanded.
-		 * @param {string}  [options.description] - Description shown at the top of the panel.
-		 * @param {number}  [options.priority=100] - The sort priority for the panel.
-		 * @param {string}  [options.templateId] - Template selector for container.
-		 * @param {string}  [options.type=default] - The type of the panel. See wp.customize.panelConstructor.
-		 * @param {string}  [options.content] - The markup to be used for the panel container. If empty, a JS template is used.
-		 * @param {boolean} [options.active=true] - Whether the panel is active or not.
-		 * @param {Object}  [options.params] - Deprecated wrapper for the above properties.
+		 * @param {string}  id                     The ID for the container.
+		 * @param {Object}  options                Object containing one property: params.
+		 * @param {string}  options.title          Title shown when panel is collapsed and expanded.
+		 * @param {string}  [options.description]  Description shown at the top of the panel.
+		 * @param {number}  [options.priority=100] The sort priority for the panel.
+		 * @param {string}  [options.templateId]   Template selector for container.
+		 * @param {string}  [options.type=default] The type of the panel. See wp.customize.panelConstructor.
+		 * @param {string}  [options.content]      The markup to be used for the panel container. If empty, a JS template is used.
+		 * @param {boolean} [options.active=true]  Whether the panel is active or not.
+		 * @param {Object}  [options.params]       Deprecated wrapper for the above properties.
 		 */
 		initialize: function ( id, options ) {
 			var container = this;
@@ -1075,7 +1080,7 @@
 		 *
 		 * @param {string} parentType
 		 * @param {string} childType
-		 * @return {Array}
+		 * @return {wp.customize.Class[]} Array of child models sorted by priority.
 		 */
 		_children: function ( parentType, childType ) {
 			var parent = this,
@@ -1109,11 +1114,11 @@
 		 *
 		 * @since 4.1.0
 		 *
-		 * @param {boolean}  active - The active state to transiution to.
-		 * @param {Object}   [args] - Args.
-		 * @param {Object}   [args.duration] - The duration for the slideUp/slideDown animation.
-		 * @param {boolean}  [args.unchanged] - Whether the state is already known to not be changed, and so short-circuit with calling completeCallback early.
-		 * @param {Function} [args.completeCallback] - Function to call when the slideUp/slideDown has completed.
+		 * @param {boolean}  active                  The active state to transiution to.
+		 * @param {Object}   [args]                  Args.
+		 * @param {Object}   [args.duration]         The duration for the slideUp/slideDown animation.
+		 * @param {boolean}  [args.unchanged]        Whether the state is already known to not be changed, and so short-circuit with calling completeCallback early.
+		 * @param {Function} [args.completeCallback] Function to call when the slideUp/slideDown has completed.
 		 */
 		onChangeActive: function( active, args ) {
 			var construct = this,
@@ -1172,8 +1177,8 @@
 		/**
 		 * @since 4.1.0
 		 *
-		 * @param {boolean} active
-		 * @param {Object}  [params]
+		 * @param {boolean} active   The active state to transition to.
+		 * @param {Object}  [params] Params.
 		 * @return {boolean} False if state already applied.
 		 */
 		_toggleActive: function ( active, params ) {
@@ -1192,7 +1197,9 @@
 		},
 
 		/**
-		 * @param {Object} [params]
+		 * Activate the control.
+		 *
+		 * @param {Object} [params] Params.
 		 * @return {boolean} False if already active.
 		 */
 		activate: function ( params ) {
@@ -1200,7 +1207,9 @@
 		},
 
 		/**
-		 * @param {Object} [params]
+		 * Deactivate the control.
+		 *
+		 * @param {Object} [params] Params.
 		 * @return {boolean} False if already inactive.
 		 */
 		deactivate: function ( params ) {
@@ -1218,9 +1227,9 @@
 		/**
 		 * 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.
+		 * @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.
 		 * @return {boolean} False if state already applied or active state is false.
 		 */
 		_toggleExpanded: function( expanded, params ) {
@@ -1234,9 +1243,9 @@
 			}
 
 			api.state( 'paneVisible' ).set( true );
-			params.completeCallback = function() {
+			params.completeCallback = function( ...args ) {
 				if ( previousCompleteCallback ) {
-					previousCompleteCallback.apply( instance, arguments );
+					previousCompleteCallback.apply( instance, args );
 				}
 				if ( expanded ) {
 					instance.container.trigger( 'expanded' );
@@ -1257,7 +1266,9 @@
 		},
 
 		/**
-		 * @param {Object} [params]
+		 * Expand the container.
+		 *
+		 * @param {Object} [params] Object containing options for expansion.
 		 * @return {boolean} False if already expanded or if inactive.
 		 */
 		expand: function ( params ) {
@@ -1265,7 +1276,9 @@
 		},
 
 		/**
-		 * @param {Object} [params]
+		 * Collapse the container.
+		 *
+		 * @param {Object} [params] Object containing options for collapse.
 		 * @return {boolean} False if already collapsed.
 		 */
 		collapse: function ( params ) {
@@ -1278,7 +1291,7 @@
 		 * @since 4.7.0
 		 * @private
 		 *
-		 * @param {function} completeCallback Function to be called after transition is completed.
+		 * @param {Function} completeCallback Function to be called after transition is completed.
 		 * @return {void}
 		 */
 		_animateChangeExpanded: function( completeCallback ) {
@@ -1352,6 +1365,7 @@
 		 * Return the container html, generated from its JS template, if it exists.
 		 *
 		 * @since 4.3.0
+		 * @return {string} Container html.
 		 */
 		getContainer: function () {
 			var template,
@@ -1429,17 +1443,17 @@
 		 *
 		 * @since 4.1.0
 		 *
-		 * @param {string}  id - The ID for the section.
-		 * @param {Object}  options - Options.
-		 * @param {string}  options.title - Title shown when section is collapsed and expanded.
-		 * @param {string}  [options.description] - Description shown at the top of the section.
-		 * @param {number}  [options.priority=100] - The sort priority for the section.
-		 * @param {string}  [options.type=default] - The type of the section. See wp.customize.sectionConstructor.
-		 * @param {string}  [options.content] - The markup to be used for the section container. If empty, a JS template is used.
-		 * @param {boolean} [options.active=true] - Whether the section is active or not.
-		 * @param {string}  options.panel - The ID for the panel this section is associated with.
-		 * @param {string}  [options.customizeAction] - Additional context information shown before the section title when expanded.
-		 * @param {Object}  [options.params] - Deprecated wrapper for the above properties.
+		 * @param {string}  id                        The ID for the section.
+		 * @param {Object}  options                   Options.
+		 * @param {string}  options.title             Title shown when section is collapsed and expanded.
+		 * @param {string}  [options.description]     Description shown at the top of the section.
+		 * @param {number}  [options.priority=100]    The sort priority for the section.
+		 * @param {string}  [options.type=default]    The type of the section. See wp.customize.sectionConstructor.
+		 * @param {string}  [options.content]         The markup to be used for the section container. If empty, a JS template is used.
+		 * @param {boolean} [options.active=true]     Whether the section is active or not.
+		 * @param {string}  options.panel             The ID for the panel this section is associated with.
+		 * @param {string}  [options.customizeAction] Additional context information shown before the section title when expanded.
+		 * @param {Object}  [options.params]          Deprecated wrapper for the above properties.
 		 */
 		initialize: function ( id, options ) {
 			var section = this, params;
@@ -1566,7 +1580,7 @@
 		 *
 		 * @since 4.1.0
 		 *
-		 * @return {boolean}
+		 * @return {boolean} True if the section has any active controls, false otherwise.
 		 */
 		isContextuallyActive: function () {
 			var section = this,
@@ -1585,7 +1599,7 @@
 		 *
 		 * @since 4.1.0
 		 *
-		 * @return {Array}
+		 * @return {wp.customize.Control[]} Array of control models sorted by priority.
 		 */
 		controls: function () {
 			return this._children( 'section', 'control' );
@@ -1596,8 +1610,8 @@
 		 *
 		 * @since 4.1.0
 		 *
-		 * @param {boolean} expanded
-		 * @param {Object}  args
+		 * @param {boolean} expanded The expanded state to transition to.
+		 * @param {Object}  args     Object containing options for expand/collapse.
 		 */
 		onChangeExpanded: function ( expanded, args ) {
 			var section = this,
@@ -1714,8 +1728,8 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string} id - ID.
-		 * @param {Object} options - Options.
+		 * @param {string} id      ID.
+		 * @param {Object} options Options.
 		 * @return {void}
 		 */
 		initialize: function( id, options ) {
@@ -1831,7 +1845,7 @@
 		 *
 		 * @since 4.2.0
 		 *
-		 * @return {boolean}
+		 * @return {boolean} True if the section is active, false otherwise.
 		 */
 		isContextuallyActive: function () {
 			return this.active();
@@ -1983,10 +1997,10 @@
 		 *
 		 * @since 4.2.0
 		 *
-		 * @param {boolean}  expanded
-		 * @param {Object}   args
-		 * @param {boolean}  args.unchanged
-		 * @param {Function} args.completeCallback
+		 * @param {boolean}  expanded              The expanded state to transition to.
+		 * @param {Object}   args                  Object containing options for expand/collapse.
+		 * @param {boolean}  args.unchanged        Whether the expanded state is unchanged.
+		 * @param {Function} args.completeCallback Callback to be executed once the expand/collapse action is complete.
 		 * @return {void}
 		 */
 		onChangeExpanded: function ( expanded, args ) {
@@ -2077,7 +2091,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @return {jQuery}
+		 * @return {jQuery} The section's content element.
 		 */
 		getContent: function() {
 			return this.container.find( '.control-section-content' );
@@ -2198,8 +2212,8 @@
 		 * Loads controls into the section from data received from loadThemes().
 		 *
 		 * @since 4.9.0
-		 * @param {Array}  themes - Array of theme data to create controls with.
-		 * @param {number} page   - Page of results being loaded.
+		 * @param {Object[]} themes Array of theme data to create controls with.
+		 * @param {number}   page   Page of results being loaded.
 		 * @return {void}
 		 */
 		loadControls: function( themes, page ) {
@@ -2252,7 +2266,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string} term - The raw search input value.
+		 * @param {string} term The raw search input value.
 		 * @return {void}
 		 */
 		filterSearch: function( term ) {
@@ -2296,7 +2310,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {wp.customize.ThemesSection} section - The current theme section, passed through the debouncer.
+		 * @param {wp.customize.ThemesSection} section The current theme section, passed through the debouncer.
 		 * @return {void}
 		 */
 		checkTerm: function( section ) {
@@ -2355,8 +2369,8 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string} newTerm - New term.
-		 * @param {Array} newTags - New tags.
+		 * @param {string}   newTerm New term.
+		 * @param {string[]} newTags New tags.
 		 * @return {void}
 		 */
 		initializeNewQuery: function( newTerm, newTags ) {
@@ -2455,6 +2469,7 @@
 		 *
 		 * @since 4.9.0
 		 *
+		 * @param {number} [count] The number of themes. Defaults to the number of visible theme controls.
 		 * @return {void}
 		 */
 		updateCount: function( count ) {
@@ -2580,7 +2595,7 @@
 		 *
 		 * @deprecated
 		 * @param {string} themeId Theme ID.
-		 * @return {jQuery.promise} Promise.
+		 * @return {JQuery.Promise<*>} Promise.
 		 */
 		loadThemePreview: function( themeId ) {
 			return api.ThemesPanel.prototype.loadThemePreview.call( this, themeId );
@@ -2591,8 +2606,8 @@
 		 *
 		 * @since 4.2.0
 		 *
-		 * @param {Object} theme - Theme.
-		 * @param {Function} [callback] - Callback once the details have been shown.
+		 * @param {Object}   theme      Theme.
+		 * @param {Function} [callback] Callback once the details have been shown.
 		 * @return {void}
 		 */
 		showDetails: function ( theme, callback ) {
@@ -2645,7 +2660,7 @@
 		 *
 		 * @since 4.2.0
 		 *
-		 * @param {jQuery} el - Element to contain focus.
+		 * @param {jQuery} el Element to contain focus.
 		 * @return {void}
 		 */
 		containFocus: function( el ) {
@@ -2687,13 +2702,15 @@
 		 *
 		 * @since 4.9.0
 		 *
+		 * @param {string} id      The ID for the section.
+		 * @param {Object} options Options, as accepted by wp.customize.Section.
 		 * @return {void}
 		 */
-		initialize: function() {
+		initialize: function( id, options ) {
 			var section = this;
 			section.containerParent = '#customize-outer-theme-controls';
 			section.containerPaneParent = '.customize-outer-pane-parent';
-			api.Section.prototype.initialize.apply( section, arguments );
+			api.Section.prototype.initialize.call( section, id, options );
 		},
 
 		/**
@@ -2702,11 +2719,11 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {boolean}  expanded - The expanded state to transition to.
-		 * @param {Object}   [args] - Args.
-		 * @param {boolean}  [args.unchanged] - Whether the state is already known to not be changed, and so short-circuit with calling completeCallback early.
-		 * @param {Function} [args.completeCallback] - Function to call when the slideUp/slideDown has completed.
-		 * @param {Object}   [args.duration] - The duration for the animation.
+		 * @param {boolean}  expanded                The expanded state to transition to.
+		 * @param {Object}   [args]                  Args.
+		 * @param {boolean}  [args.unchanged]        Whether the state is already known to not be changed, and so short-circuit with calling completeCallback early.
+		 * @param {Function} [args.completeCallback] Function to call when the slideUp/slideDown has completed.
+		 * @param {Object}   [args.duration]         The duration for the animation.
 		 */
 		onChangeExpanded: function( expanded, args ) {
 			var section = this,
@@ -2792,15 +2809,15 @@
 		 *
 		 * @since 4.1.0
 		 *
-		 * @param {string}  id - The ID for the panel.
-		 * @param {Object}  options - Object containing one property: params.
-		 * @param {string}  options.title - Title shown when panel is collapsed and expanded.
-		 * @param {string}  [options.description] - Description shown at the top of the panel.
-		 * @param {number}  [options.priority=100] - The sort priority for the panel.
-		 * @param {string}  [options.type=default] - The type of the panel. See wp.customize.panelConstructor.
-		 * @param {string}  [options.content] - The markup to be used for the panel container. If empty, a JS template is used.
-		 * @param {boolean} [options.active=true] - Whether the panel is active or not.
-		 * @param {Object}  [options.params] - Deprecated wrapper for the above properties.
+		 * @param {string}  id                     The ID for the panel.
+		 * @param {Object}  options                Object containing one property: params.
+		 * @param {string}  options.title          Title shown when panel is collapsed and expanded.
+		 * @param {string}  [options.description]  Description shown at the top of the panel.
+		 * @param {number}  [options.priority=100] The sort priority for the panel.
+		 * @param {string}  [options.type=default] The type of the panel. See wp.customize.panelConstructor.
+		 * @param {string}  [options.content]      The markup to be used for the panel container. If empty, a JS template is used.
+		 * @param {boolean} [options.active=true]  Whether the panel is active or not.
+		 * @param {Object}  [options.params]       Deprecated wrapper for the above properties.
 		 */
 		initialize: function ( id, options ) {
 			var panel = this, params;
@@ -2906,7 +2923,7 @@
 		 *
 		 * @since 4.1.0
 		 *
-		 * @return {Array}
+		 * @return {wp.customize.Section[]} Array of sections.
 		 */
 		sections: function () {
 			return this._children( 'panel', 'section' );
@@ -3050,7 +3067,7 @@
 		}
 	});
 
-	api.ThemesPanel = api.Panel.extend(/** @lends wp.customize.ThemsPanel.prototype */{
+	api.ThemesPanel = api.Panel.extend(/** @lends wp.customize.ThemesPanel.prototype */{
 
 		/**
 		 *  Class wp.customize.ThemesPanel.
@@ -3062,8 +3079,8 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string} id - The ID for the panel.
-		 * @param {Object} options - Options.
+		 * @param {string} id      The ID for the panel.
+		 * @param {Object} options Options.
 		 * @return {void}
 		 */
 		initialize: function( id, options ) {
@@ -3077,7 +3094,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string} [slug] - Theme slug.
+		 * @param {string} [slug] Theme slug. When omitted, whether switching is possible at all.
 		 * @return {boolean} Whether the theme can be switched to.
 		 */
 		canSwitchTheme: function canSwitchTheme( slug ) {
@@ -3160,10 +3177,10 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {boolean}  expanded - Expanded state.
-		 * @param {Object}   args - Args.
-		 * @param {boolean}  args.unchanged - Whether or not the state changed.
-		 * @param {Function} args.completeCallback - Callback to execute when the animation completes.
+		 * @param {boolean}  expanded              Expanded state.
+		 * @param {Object}   args                  Args.
+		 * @param {boolean}  args.unchanged        Whether or not the state changed.
+		 * @param {Function} args.completeCallback Callback to execute when the animation completes.
 		 * @return {void}
 		 */
 		onChangeExpanded: function( expanded, args ) {
@@ -3215,8 +3232,8 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {jQuery.Event} event - Event.
-		 * @return {jQuery.promise} Promise.
+		 * @param {JQuery.Event} event Event.
+		 * @return {JQuery.Promise<*>} Promise.
 		 */
 		installTheme: function( event ) {
 			var panel = this, preview, onInstallSuccess, slug = $( event.target ).data( 'slug' ), deferred = $.Deferred(), request;
@@ -3321,7 +3338,7 @@
 		 * @since 4.9.0
 		 *
 		 * @param {string} themeId Theme ID.
-		 * @return {jQuery.promise} Promise.
+		 * @return {JQuery.Promise<*>} Promise.
 		 */
 		loadThemePreview: function( themeId ) {
 			var panel = this, deferred = $.Deferred(), onceProcessingComplete, urlParser, queryParams;
@@ -3396,7 +3413,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {jQuery.Event} event - Event.
+		 * @param {JQuery.Event} event Event.
 		 * @return {void}
 		 */
 		updateTheme: function( event ) {
@@ -3426,7 +3443,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {jQuery.Event} event - Event.
+		 * @param {JQuery.Event} event Event.
 		 * @return {void}
 		 */
 		deleteTheme: function( event ) {
@@ -3484,7 +3501,7 @@
 		 * Default params.
 		 *
 		 * @since 4.9.0
-		 * @var {object}
+		 * @member {Object}
 		 */
 		defaults: {
 			label: '',
@@ -3508,22 +3525,22 @@
 		 * @borrows wp.customize~Container#deactivate as this#deactivate
 		 * @borrows wp.customize~Container#_toggleActive as this#_toggleActive
 		 *
-		 * @param {string} id                       - Unique identifier for the control instance.
-		 * @param {Object} options                  - Options hash for the control instance.
-		 * @param {Object} options.type             - Type of control (e.g. text, radio, dropdown-pages, etc.)
-		 * @param {string} [options.content]        - The HTML content for the control or at least its container. This should normally be left blank and instead supplying a templateId.
-		 * @param {string} [options.templateId]     - Template ID for control's content.
-		 * @param {string} [options.priority=10]    - Order of priority to show the control within the section.
-		 * @param {string} [options.active=true]    - Whether the control is active.
-		 * @param {string} options.section          - The ID of the section the control belongs to.
-		 * @param {mixed}  [options.setting]        - The ID of the main setting or an instance of this setting.
-		 * @param {mixed}  options.settings         - An object with keys (e.g. default) that maps to setting IDs or Setting/Value objects, or an array of setting IDs or Setting/Value objects.
-		 * @param {mixed}  options.settings.default - The ID of the setting the control relates to.
-		 * @param {string} options.settings.data    - @todo Is this used?
-		 * @param {string} options.label            - Label.
-		 * @param {string} options.description      - Description.
-		 * @param {number} [options.instanceNumber] - Order in which this instance was created in relation to other instances.
-		 * @param {Object} [options.params]         - Deprecated wrapper for the above properties.
+		 * @param {string} id                       Unique identifier for the control instance.
+		 * @param {Object} options                  Options hash for the control instance.
+		 * @param {Object} options.type             Type of control (e.g. text, radio, dropdown-pages, etc.)
+		 * @param {string} [options.content]        The HTML content for the control or at least its container. This should normally be left blank and instead supplying a templateId.
+		 * @param {string} [options.templateId]     Template ID for control's content.
+		 * @param {string} [options.priority=10]    Order of priority to show the control within the section.
+		 * @param {string} [options.active=true]    Whether the control is active.
+		 * @param {string} options.section          The ID of the section the control belongs to.
+		 * @param {*}      [options.setting]        The ID of the main setting or an instance of this setting.
+		 * @param {*}      options.settings         An object with keys (e.g. default) that maps to setting IDs or Setting/Value objects, or an array of setting IDs or Setting/Value objects.
+		 * @param {*}      options.settings.default The ID of the setting the control relates to.
+		 * @param {string} options.settings.data    @todo Is this used?
+		 * @param {string} options.label            Label.
+		 * @param {string} options.description      Description.
+		 * @param {number} [options.instanceNumber] Order in which this instance was created in relation to other instances.
+		 * @param {Object} [options.params]         Deprecated wrapper for the above properties.
 		 * @return {void}
 		 */
 		initialize: function( id, options ) {
@@ -3909,7 +3926,7 @@
 		/**
 		 * Normal controls do not expand, so just expand its parent
 		 *
-		 * @param {Object} [params]
+		 * @param {Object} [params] Parameters to pass to the section's expand method.
 		 */
 		expand: function ( params ) {
 			api.section( this.section() ).expand( params );
@@ -3954,7 +3971,11 @@
 		},
 
 		/**
+		 * Toggle the control's active state.
+		 *
+		 * @param {boolean} active The active state to toggle.
 		 * @deprecated 4.1.0 Use this.onChangeActive() instead.
+		 * @return {void}
 		 */
 		toggle: function ( active ) {
 			return this.onChangeActive( active, this.defaultActiveArguments );
@@ -4263,7 +4284,7 @@
 			 * and it is the responsibility of the UploadControl to set the control's
 			 * attachmentData before calling the renderContent method.
 			 *
-			 * @param {number|string} value Attachment
+			 * @param {number|string} value Attachment.
 			 */
 			function setAttachmentDataAndRenderContent( value ) {
 				var hasAttachmentData = $.Deferred();
@@ -4313,6 +4334,8 @@
 
 		/**
 		 * Open the media modal.
+		 *
+		 * @param {Object} event jQuery Event object
 		 */
 		openFrame: function( event ) {
 			if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
@@ -4376,6 +4399,8 @@
 
 		/**
 		 * Reset the setting to the default value.
+		 *
+		 * @param {Object} event jQuery Event object.
 		 */
 		restoreDefault: function( event ) {
 			if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
@@ -4390,7 +4415,7 @@
 		/**
 		 * Called when the "Remove" link is clicked. Empties the setting.
 		 *
-		 * @param {Object} event jQuery Event object
+		 * @param {Object} event jQuery Event object.
 		 */
 		removeFile: function( event ) {
 			if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
@@ -4470,7 +4495,7 @@
 		 * set up internal event bindings.
 		 */
 		ready: function() {
-			api.UploadControl.prototype.ready.apply( this, arguments );
+			api.UploadControl.prototype.ready.call( this );
 		},
 
 		/**
@@ -4478,7 +4503,7 @@
 		 * Does an additional Ajax request for setting the background context.
 		 */
 		select: function() {
-			api.UploadControl.prototype.select.apply( this, arguments );
+			api.UploadControl.prototype.select.call( this );
 
 			wp.ajax.post( 'custom-background-add', {
 				nonce: _wpCustomizeBackground.nonces.add,
@@ -4539,6 +4564,8 @@
 
 		/**
 		 * Open the media modal to the library state.
+		 *
+		 * @param {Object} event jQuery Event object.
 		 */
 		openFrame: function( event ) {
 			if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
@@ -4611,8 +4638,8 @@
 		 * 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
+		 * @param {wp.media.model.Attachment}   attachment The attachment to be cropped.
+		 * @param {wp.media.controller.Cropper} controller The cropper controller.
 		 * @return {Object} Options
 		 */
 		calculateImageSelectOptions: function( attachment, controller ) {
@@ -4874,7 +4901,7 @@
 		/**
 		 * Called when the "Remove" link is clicked. Empties the setting.
 		 *
-		 * @param {Object} event jQuery Event object
+		 * @param {Object} event jQuery Event object.
 		 */
 		removeFile: function( event ) {
 			if ( api.utils.isKeydownButNotEnterEvent( event ) ) {
@@ -4967,8 +4994,8 @@
 		 * theme-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
+		 * @param {wp.media.model.Attachment}   attachment The attachment to be cropped.
+		 * @param {wp.media.controller.Cropper} controller The cropper controller.
 		 * @return {Object} Options
 		 */
 		calculateImageSelectOptions: function(attachment, controller) {
@@ -5038,7 +5065,7 @@
 		 * current theme, a cropping step after selection may be required or
 		 * skippable.
 		 *
-		 * @param {event} event
+		 * @param {JQuery.Event} event Event.
 		 */
 		openMedia: function(event) {
 			var l10n = _wpMediaViewsL10n;
@@ -5237,7 +5264,7 @@
 		 * Show or hide the theme based on the presence of the term in the title, description, tags, and author.
 		 *
 		 * @since 4.2.0
-		 * @param {Array} terms - An array of terms to search for.
+		 * @param {string[]} terms An array of terms to search for.
 		 * @return {boolean} Whether a theme control was activated or not.
 		 */
 		filter: function( terms ) {
@@ -5288,6 +5315,7 @@
 		/**
 		 * Rerender the theme from its JS template with the installed type.
 		 *
+		 * @param {boolean} installed Whether the theme is installed.
 		 * @since 4.9.0
 		 *
 		 * @return {void}
@@ -5319,8 +5347,8 @@
 		 * Initialize.
 		 *
 		 * @since 4.9.0
-		 * @param {string} id      - Unique identifier for the control instance.
-		 * @param {Object} options - Options hash for the control instance.
+		 * @param {string} id      Unique identifier for the control instance.
+		 * @param {Object} options Options hash for the control instance.
 		 * @return {void}
 		 */
 		initialize: function( id, options ) {
@@ -5437,8 +5465,8 @@
 		 * Make sure editor gets focused when control is focused.
 		 *
 		 * @since 4.9.0
-		 * @param {Object}   [params] - Focus params.
-		 * @param {Function} [params.completeCallback] - Function to call when expansion is complete.
+		 * @param {Object}   [params]                  Focus params.
+		 * @param {Function} [params.completeCallback] Function to call when expansion is complete.
 		 * @return {void}
 		 */
 		focus: function( params ) {
@@ -5459,7 +5487,7 @@
 		 * Initialize syntax-highlighting editor.
 		 *
 		 * @since 4.9.0
-		 * @param {Object} codeEditorSettings - Code editor settings.
+		 * @param {Object} codeEditorSettings Code editor settings.
 		 * @return {void}
 		 */
 		initSyntaxHighlightingEditor: function( codeEditorSettings ) {
@@ -5555,7 +5583,7 @@
 		 * Update error notice.
 		 *
 		 * @since 4.9.0
-		 * @param {Array} errorAnnotations - Error annotations.
+		 * @param {Object[]} errorAnnotations Error annotations.
 		 * @return {void}
 		 */
 		onUpdateErrorNotice: function onUpdateErrorNotice( errorAnnotations ) {
@@ -5700,7 +5728,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string} datetime - Date/Time string. Accepts Y-m-d[ H:i[:s]] format.
+		 * @param {string} datetime Date/Time string. Accepts Y-m-d[ H:i[:s]] format.
 		 * @return {Object|null} Returns object containing date components or null if parse error.
 		 */
 		parseDateTime: function parseDateTime( datetime ) {
@@ -5888,8 +5916,8 @@
 		 * Convert hour in twelve hour format to twenty four hour format.
 		 *
 		 * @since 4.9.0
-		 * @param {string} hourInTwelveHourFormat - Hour in twelve hour format.
-		 * @param {string} meridian - Either 'am' or 'pm'.
+		 * @param {string} hourInTwelveHourFormat Hour in twelve hour format.
+		 * @param {string} meridian               Either 'am' or 'pm'.
 		 * @return {string} Hour in twenty four hour format.
 		 */
 		convertHourToTwentyFourHourFormat: function convertHour( hourInTwelveHourFormat, meridian ) {
@@ -5959,7 +5987,7 @@
 		 *
 		 * @since 4.9.0
 		 * @param {boolean} notify Add or remove the notification.
-		 * @return {wp.customize.DateTimeControl}
+		 * @return {wp.customize.DateTimeControl} The date control instance.
 		 */
 		toggleFutureDateNotification: function toggleFutureDateNotification( notify ) {
 			var control = this, notificationCode, notification;
@@ -6123,9 +6151,9 @@
 	 * @since 3.4.0
 	 *
 	 * @type {Function}
-	 * @param {...string} ids - One or more ids for controls to obtain.
-	 * @param {deferredControlsCallback} [callback] - Function called when all supplied controls exist.
-	 * @return {wp.customize.Control|undefined|jQuery.promise} Control instance or undefined (if function called with one id param),
+	 * @param {...string}                             ids        One or more ids for controls to obtain.
+	 * @param {wp.customize.deferredControlsCallback} [callback] Function called when all supplied controls exist.
+	 * @return {wp.customize.Control|undefined|JQuery.Promise<*>} Control instance or undefined (if function called with one id param),
 	 *                                                         or promise resolving to requested controls.
 	 *
 	 * @example <caption>Loop over all registered controls.</caption>
@@ -6185,9 +6213,9 @@
 	 * @since 3.4.0
 	 *
 	 * @type {Function}
-	 * @param {...string} ids - One or more ids for sections to obtain.
-	 * @param {deferredSectionsCallback} [callback] - Function called when all supplied sections exist.
-	 * @return {wp.customize.Section|undefined|jQuery.promise} Section instance or undefined (if function called with one id param),
+	 * @param {...string}                             ids        One or more ids for sections to obtain.
+	 * @param {wp.customize.deferredSectionsCallback} [callback] Function called when all supplied sections exist.
+	 * @return {wp.customize.Section|undefined|JQuery.Promise<*>} Section instance or undefined (if function called with one id param),
 	 *                                                         or promise resolving to requested sections.
 	 *
 	 * @example <caption>Loop over all registered sections.</caption>
@@ -6220,9 +6248,9 @@
 	 * @since 4.0.0
 	 *
 	 * @type {Function}
-	 * @param {...string} ids - One or more ids for panels to obtain.
-	 * @param {deferredPanelsCallback} [callback] - Function called when all supplied panels exist.
-	 * @return {wp.customize.Panel|undefined|jQuery.promise} Panel instance or undefined (if function called with one id param),
+	 * @param {...string}                           ids        One or more ids for panels to obtain.
+	 * @param {wp.customize.deferredPanelsCallback} [callback] Function called when all supplied panels exist.
+	 * @return {wp.customize.Panel|undefined|JQuery.Promise<*>} Panel instance or undefined (if function called with one id param),
 	 *                                                       or promise resolving to requested panels.
 	 *
 	 * @example <caption>Loop over all registered panels.</caption>
@@ -6255,9 +6283,9 @@
 	 * @since 4.9.0
 	 *
 	 * @type {Function}
-	 * @param {...string} codes - One or more codes for notifications to obtain.
-	 * @param {deferredNotificationsCallback} [callback] - Function called when all supplied notifications exist.
-	 * @return {wp.customize.Notification|undefined|jQuery.promise} Notification instance or undefined (if function called with one code param),
+	 * @param {...string}                                  codes      One or more codes for notifications to obtain.
+	 * @param {wp.customize.deferredNotificationsCallback} [callback] Function called when all supplied notifications exist.
+	 * @return {wp.customize.Notification|undefined|JQuery.Promise<*>} Notification instance or undefined (if function called with one code param),
 	 *                                                              or promise resolving to requested notifications.
 	 *
 	 * @example <caption>Check if existing notification</caption>
@@ -6293,10 +6321,11 @@
 		 * @constructs wp.customize.PreviewFrame
 		 * @augments   wp.customize.Messenger
 		 *
-		 * @param {Object} params.container
-		 * @param {Object} params.previewUrl
-		 * @param {Object} params.query
-		 * @param {Object} options
+		 * @param {Object} params            The parameters object.
+		 * @param {Object} params.container  The container element for the preview frame.
+		 * @param {string} params.previewUrl The URL of the preview.
+		 * @param {Object} params.query      The query parameters for the preview URL.
+		 * @param {Object} options           The options object.
 		 */
 		initialize: function( params, options ) {
 			var deferred = $.Deferred();
@@ -6500,7 +6529,7 @@
 		 * misnomer as it is not an actual UUID, and it is not universally unique.
 		 * This is not to be confused with `api.settings.changeset.uuid`.
 		 *
-		 * @return {string}
+		 * @return {string} A unique ID for a preview messenger channel.
 		 */
 		api.PreviewFrame.uuid = function() {
 			return 'preview-' + String( id++ );
@@ -6531,12 +6560,13 @@
 		 * @constructs wp.customize.Previewer
 		 * @augments   wp.customize.Messenger
 		 *
-		 * @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 {Object} options
+		 * @param {Object}   params             The parameters object.
+		 * @param {string[]} params.allowedUrls An array of allowed URLs for the preview.
+		 * @param {string}   params.container   A selector or jQuery element for the preview
+		 *                                      frame to be placed.
+		 * @param {string} params.form 	        A selector or jQuery element for the form to be used for POSTing data to the preview frame.
+		 * @param {string} params.previewUrl    The URL to preview.
+		 * @param {Object} options              The options object.
 		 */
 		initialize: function( params, options ) {
 			var previewer = this,
@@ -6684,9 +6714,9 @@
 		 * @since 4.7.0
 		 * @access public
 		 *
-		 * @param {Object} data - Data from preview.
-		 * @param {string} data.currentUrl - Current URL.
-		 * @param {Object} data.activePanels - Active panels.
+		 * @param {Object} data                Data from preview.
+		 * @param {string} data.currentUrl     Current URL.
+		 * @param {Object} data.activePanels   Active panels.
 		 * @param {Object} data.activeSections Active sections.
 		 * @param {Object} data.activeControls Active controls.
 		 * @return {void}
@@ -7068,7 +7098,7 @@
 	 *
 	 * @since 4.6.0
 	 * @param {string[]} settingIds Setting IDs.
-	 * @return {Object<string, wp.customize.Control>} Mapping setting ids to arrays of controls.
+	 * @return {Object.<string, wp.customize.Control>} Mapping setting ids to arrays of controls.
 	 */
 	api.findControlsForSettings = function findControlsForSettings( settingIds ) {
 		var controls = {}, settingControls;
@@ -7476,7 +7506,7 @@
 			 * @since 4.7.0 Added options param.
 			 * @access public
 			 *
-			 * @param {Object}  [options] Options.
+			 * @param {Object}  [options]                              Options.
 			 * @param {boolean} [options.excludeCustomizedSaved=false] Exclude saved settings in customized response (values pending writing to changeset).
 			 * @return {Object} Query vars.
 			 */
@@ -7514,11 +7544,11 @@
 			 * @since 3.4.0
 			 * @since 4.7.0 Added args param and return value.
 			 *
-			 * @param {Object} [args] Args.
+			 * @param {Object} [args]                Args.
 			 * @param {string} [args.status=publish] Status.
-			 * @param {string} [args.date] Date, in local time in MySQL format.
-			 * @param {string} [args.title] Title
-			 * @return {jQuery.promise} Promise.
+			 * @param {string} [args.date]           Date, in local time in MySQL format.
+			 * @param {string} [args.title]          Title.
+			 * @return {JQuery.Promise<*>} Promise.
 			 */
 			save: function( args ) {
 				var previewer = this,
@@ -7790,8 +7820,6 @@
 			 * Revert the Customizer to its previously-published state.
 			 *
 			 * @since 4.9.0
-			 *
-			 * @return {jQuery.promise} Promise.
 			 */
 			trash: function trash() {
 				var request, success, fail;
@@ -8183,7 +8211,7 @@
 				/**
 				 * Lock user.
 				 *
-				 * @type {object}
+				 * @type {Object}
 				 */
 				lockUser: null,
 
@@ -8195,8 +8223,8 @@
 				 *
 				 * @since 4.9.0
 				 *
-				 * @param {string} [code] - Code.
-				 * @param {Object} [params] - Params.
+				 * @param {string} [code]   Code.
+				 * @param {Object} [params] Params.
 				 */
 				initialize: function( code, params ) {
 					var notification = this, _code, _params;
@@ -8285,9 +8313,9 @@
 			 *
 			 * @since 4.9.0
 			 *
-			 * @param {Object} [args] - Args.
-			 * @param {Object} [args.lockUser] - Lock user data.
-			 * @param {boolean} [args.allowOverride=false] - Whether override is allowed.
+			 * @param {Object} [args]                      Args.
+			 * @param {Object} [args.lockUser]             Lock user data.
+			 * @param {boolean} [args.allowOverride=false] Whether override is allowed.
 			 * @return {void}
 			 */
 			function startLock( args ) {
@@ -8367,7 +8395,7 @@
 			/**
 			 * Remove parameter from the URL.
 			 *
-			 * @param {Array} params - Parameter names to remove.
+			 * @param {string[]} params Parameter names to remove.
 			 * @return {void}
 			 */
 			function stripParamsFromLocation( params ) {
@@ -8393,7 +8421,7 @@
 			 *
 			 * @since 4.9.0
 			 *
-			 * @param {string} [notification] - A notification to display.
+			 * @param {string} [notification] A notification to display.
 			 * @return {void}
 			 */
 			function addSiteEditorNotification( notification ) {
@@ -8750,9 +8778,9 @@
 			 * @since 4.7.0
 			 * @access private
 			 *
-			 * @param {Object} header - Header.
-			 * @param {number} scrollTop - Scroll top.
-			 * @param {number} scrollDirection - Scroll direction, negative number being up and positive being down.
+			 * @param {Object} header          Header.
+			 * @param {number} scrollTop       Scroll top.
+			 * @param {number} scrollDirection Scroll direction, negative number being up and positive being down.
 			 * @return {void}
 			 */
 			positionStickyHeader = function( header, scrollTop, scrollDirection ) {
diff --git a/src/js/_enqueues/wp/customize/loader.js b/src/js/_enqueues/wp/customize/loader.js
index 2326f1f7dfccc..b4aaa12b9ed12 100644
--- a/src/js/_enqueues/wp/customize/loader.js
+++ b/src/js/_enqueues/wp/customize/loader.js
@@ -12,7 +12,11 @@
  */
 window.wp = window.wp || {};
 
-(function( exports, $ ){
+/**
+ * @param {Object}       wp The WordPress global object.
+ * @param {JQueryStatic} $  The jQuery object.
+ */
+(function( wp, $ ){
 	var api = wp.customize,
 		Loader;
 
@@ -76,6 +80,12 @@ window.wp = window.wp || {};
 			}
 		},
 
+		/**
+		 * Handle popstate event.
+		 *
+		 * @param {JQuery.Event} e The popstate event.
+		 * @return {void}
+		 */
 		popstate: function( e ) {
 			var state = e.originalEvent.state;
 			if ( state && state.customize ) {
@@ -85,6 +95,9 @@ window.wp = window.wp || {};
 			}
 		},
 
+		/**
+		 * Handle hashchange event.
+		 */
 		hashchange: function() {
 			var hash = window.location.toString().split('#')[1];
 
@@ -97,6 +110,11 @@ window.wp = window.wp || {};
 			}
 		},
 
+		/**
+		 * Handle beforeunload event.
+		 *
+		 * @return {string|void} Confirmation message if there are unsaved changes.
+		 */
 		beforeunload: function () {
 			if ( ! Loader.saved() ) {
 				return Loader.settings.l10n.saveAlert;
@@ -106,7 +124,8 @@ window.wp = window.wp || {};
 		/**
 		 * Open the Customizer overlay for a specific URL.
 		 *
-		 * @param string src URL to load in the Customizer.
+		 * @param {string} src URL to load in the Customizer.
+		 * @return {string|void} The URL, when navigating to it directly on mobile.
 		 */
 		open: function( src ) {
 
@@ -189,6 +208,11 @@ window.wp = window.wp || {};
 			this.trigger( 'open' );
 		},
 
+		/**
+		 * Push the state of the Customizer onto the history stack.
+		 *
+		 * @param {string} src URL to push.
+		 */
 		pushState: function ( src ) {
 			var hash = src.split( '?' )[1];
 
@@ -270,10 +294,16 @@ window.wp = window.wp || {};
 		 * Overlay hide/show utility methods.
 		 */
 		overlay: {
+			/**
+			 * Show the overlay.
+			 */
 			show: function() {
 				this.element.fadeIn( 200, Loader.opened );
 			},
 
+			/**
+			 * Hide the overlay.
+			 */
 			hide: function() {
 				this.element.fadeOut( 200, Loader.closed );
 			}
diff --git a/src/js/_enqueues/wp/customize/models.js b/src/js/_enqueues/wp/customize/models.js
index e72266327a333..731d29fbb9d90 100644
--- a/src/js/_enqueues/wp/customize/models.js
+++ b/src/js/_enqueues/wp/customize/models.js
@@ -3,6 +3,11 @@
  */
 
 /* global _wpCustomizeHeader */
+
+/**
+ * @param {JQueryStatic} $  The jQuery object.
+ * @param {Object}       wp The WordPress global object.
+ */
 (function( $, wp ) {
 	var api = wp.customize;
 	/** @namespace wp.customize.HeaderTool */
@@ -21,10 +26,15 @@
 	 * @memberOf wp.customize.HeaderTool
 	 * @alias wp.customize.HeaderTool.ImageModel
 	 *
-	 * @constructor
+	 * @class
 	 * @augments Backbone.Model
 	 */
 	api.HeaderTool.ImageModel = Backbone.Model.extend(/** @lends wp.customize.HeaderTool.ImageModel.prototype */{
+		/**
+		 * Default attributes.
+		 *
+		 * @return {Object} Default attributes.
+		 */
 		defaults: function() {
 			return {
 				header: {
@@ -39,16 +49,25 @@
 			};
 		},
 
+		/**
+		 * Initialize.
+		 */
 		initialize: function() {
 			this.on('hide', this.hide, this);
 		},
 
+		/**
+		 * Hide.
+		 */
 		hide: function() {
 			this.set('choice', '');
 			api('header_image').set('remove-header');
 			api('header_image_data').set('remove-header');
 		},
 
+		/**
+		 * Destroy.
+		 */
 		destroy: function() {
 			var data = this.get('header'),
 				curr = api.HeaderTool.currentHeader.get('header').attachment_id;
@@ -69,6 +88,9 @@
 			this.trigger('destroy', this, this.collection);
 		},
 
+		/**
+		 * Save.
+		 */
 		save: function() {
 			if (this.get('random')) {
 				api('header_image').set(this.get('header').random);
@@ -86,6 +108,9 @@
 			api.HeaderTool.combinedList.trigger('control:setImage', this);
 		},
 
+		/**
+		 * Import image.
+		 */
 		importImage: function() {
 			var data = this.get('header');
 			if (data.attachment_id === undefined) {
@@ -100,6 +125,11 @@
 			} );
 		},
 
+		/**
+		 * Should be cropped.
+		 *
+		 * @return {boolean} Whether the image should be cropped.
+		 */
 		shouldBeCropped: function() {
 			if (this.get('themeFlexWidth') === true &&
 						this.get('themeFlexHeight') === true) {
@@ -136,17 +166,25 @@
 	 * @memberOf wp.customize.HeaderTool
 	 * @alias wp.customize.HeaderTool.ChoiceList
 	 *
-	 * @constructor
+	 * @class
 	 * @augments Backbone.Collection
 	 */
 	api.HeaderTool.ChoiceList = Backbone.Collection.extend({
 		model: api.HeaderTool.ImageModel,
 
-		// Ordered from most recently used to least.
+		/**
+		 * Comparator which orders the collection from most recently used to least.
+		 *
+		 * @param {Backbone.Model} model The model to sort.
+		 * @return {number} The sort order.
+		 */
 		comparator: function(model) {
 			return -model.get('header').timestamp;
 		},
 
+		/**
+		 * Initialize.
+		 */
 		initialize: function() {
 			var current = api.HeaderTool.currentHeader.get('choice').replace(/^https?:\/\//, ''),
 				isRandom = this.isRandomChoice(api.get().header_image);
@@ -192,6 +230,11 @@
 			}
 		},
 
+		/**
+		 * Maybe remove old crop.
+		 *
+		 * @param {Backbone.Model} model Model.
+		 */
 		maybeRemoveOldCrop: function( model ) {
 			var newID = model.get( 'header' ).attachment_id || false,
 			 	oldCrop;
@@ -211,12 +254,20 @@
 			}
 		},
 
+		/**
+		 * Maybe add random choice.
+		 */
 		maybeAddRandomChoice: function() {
 			if (this.size() === 1) {
 				this.addRandomChoice();
 			}
 		},
 
+		/**
+		 * Add random choice.
+		 *
+		 * @param {string} initialChoice Initial choice.
+		 */
 		addRandomChoice: function(initialChoice) {
 			var isRandomSameType = RegExp(this.type).test(initialChoice),
 				randomChoice = 'random-' + this.type + '-image';
@@ -234,14 +285,30 @@
 			});
 		},
 
+		/**
+		 * Is random choice?
+		 *
+		 * @param {string} choice Choice.
+		 * @return {boolean} Whether the choice is random.
+		 */
 		isRandomChoice: function(choice) {
 			return (/^random-(uploaded|default)-image$/).test(choice);
 		},
 
+		/**
+		 * Should hide title?
+		 *
+		 * @return {boolean} Whether the title should be hidden.
+		 */
 		shouldHideTitle: function() {
 			return this.size() < 2;
 		},
 
+		/**
+		 * Set image.
+		 *
+		 * @param {Backbone.Model} model Model.
+		 */
 		setImage: function(model) {
 			this.each(function(m) {
 				m.set('selected', false);
@@ -252,6 +319,9 @@
 			}
 		},
 
+		/**
+		 * Remove image.
+		 */
 		removeImage: function() {
 			this.each(function(m) {
 				m.set('selected', false);
@@ -266,11 +336,14 @@
 	 * @memberOf wp.customize.HeaderTool
 	 * @alias wp.customize.HeaderTool.DefaultsList
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.customize.HeaderTool.ChoiceList
 	 * @augments Backbone.Collection
 	 */
 	api.HeaderTool.DefaultsList = api.HeaderTool.ChoiceList.extend({
+		/**
+		 * Initialize.
+		 */
 		initialize: function() {
 			this.type = 'default';
 			this.data = _wpCustomizeHeader.defaults;
diff --git a/src/js/_enqueues/wp/customize/nav-menus.js b/src/js/_enqueues/wp/customize/nav-menus.js
index 607740014e5e4..5bebe8ea9f07f 100644
--- a/src/js/_enqueues/wp/customize/nav-menus.js
+++ b/src/js/_enqueues/wp/customize/nav-menus.js
@@ -3,6 +3,12 @@
  */
 
 /* global menus, _wpCustomizeNavMenusSettings, wpNavMenu, console */
+
+/**
+ * @param {Object}       api The Customizer API.
+ * @param {Object}       wp  The WordPress global object.
+ * @param {JQueryStatic} $   The jQuery object.
+ */
 ( function( api, wp, $ ) {
 	'use strict';
 
@@ -44,7 +50,7 @@
 	 *
 	 * @alias wp.customize.Menus.generatePlaceholderAutoIncrementId
 	 *
-	 * @return {number}
+	 * @return {number} A negative integer ID.
 	 */
 	api.Menus.generatePlaceholderAutoIncrementId = function() {
 		return -Math.ceil( api.Menus.data.phpIntMax * Math.random() );
@@ -95,10 +101,10 @@
 	 * @since 4.7.0
 	 * @alias wp.customize.Menus.insertAutoDraftPost
 	 *
-	 * @param {Object} params - Parameters for the draft post to create.
-	 * @param {string} params.post_type - Post type to add.
-	 * @param {string} params.post_title - Post title to use.
-	 * @return {jQuery.promise} Promise resolved with the added post.
+	 * @param {Object} params            Parameters for the draft post to create.
+	 * @param {string} params.post_type  Post type to add.
+	 * @param {string} params.post_title Post title to use.
+	 * @return {JQuery.Promise<*>} Promise resolved with the added post.
 	 */
 	api.Menus.insertAutoDraftPost = function insertAutoDraftPost( params ) {
 		var request, deferred = $.Deferred();
@@ -390,7 +396,7 @@
 		 * @since 4.7.0 Changed function signature to take list of item types instead of single type/object.
 		 * @access private
 		 *
-		 * @param {Array.<Object>} itemTypes List of objects containing type and key.
+		 * @param {Object[]} itemTypes List of objects containing type and key.
 		 * @param {string} deprecated Formerly the object parameter.
 		 * @return {void}
 		 */
@@ -630,7 +636,7 @@
 		 * @since 4.7.0
 		 * @private
 		 *
-		 * @param {jQuery.Event} event Event.
+		 * @param {JQuery.Event} event Event.
 		 * @return {void}
 		 */
 		_submitNew: function( event ) {
@@ -919,7 +925,7 @@
 		 * @since 4.3.0
 		 * @private
 		 *
-		 * @return {Array} Fields (columns) that are hidden.
+		 * @return {string} Comma separated list of the fields (columns) that are hidden.
 		 */
 		hidden: function() {
 			return $( '.hide-column-tog' ).not( ':checked' ).map( function() {
@@ -1141,7 +1147,7 @@
 		},
 
 		/**
-		 * @param {Array} themeLocationSlugs Theme location slugs.
+		 * @param {string[]} themeLocationSlugs Theme location slugs.
 		 */
 		updateAssignedLocationsInSectionTitle: function( themeLocationSlugs ) {
 			var section = this,
@@ -1334,7 +1340,7 @@
 			 * Handle setting addition.
 			 *
 			 * @since 4.9.0
-			 * @param {wp.customize.Setting} setting - Added setting.
+			 * @param {wp.customize.Setting} setting Added setting.
 			 * @return {void}
 			 */
 			function addChangeEventListener( setting ) {
@@ -1348,7 +1354,7 @@
 			 * Handle setting removal.
 			 *
 			 * @since 4.9.0
-			 * @param {wp.customize.Setting} setting - Removed setting.
+			 * @param {wp.customize.Setting} setting Removed setting.
 			 * @return {void}
 			 */
 			function removeChangeEventListener( setting ) {
@@ -1363,7 +1369,7 @@
 			api.bind( 'removed', removeChangeEventListener );
 			updateNoticeVisibility();
 
-			api.Section.prototype.attachEvents.apply( section, arguments );
+			api.Section.prototype.attachEvents.call( section );
 		},
 
 		/**
@@ -1483,7 +1489,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {string|null} locationId - The ID of the location to select. `null` clears all selections.
+		 * @param {string|null} locationId The ID of the location to select. `null` clears all selections.
 		 * @return {void}
 		 */
 		selectDefaultLocation: function( locationId ) {
@@ -1643,7 +1649,7 @@
 		 * Shows or hides buttons based on the location of the menu item.
 		 *
 		 * @param {Object} itemToRefresh The menu item that might need its advanced accessibility buttons refreshed
-		 * 
+		 *
 		 * @since 6.6.0
 		 */
 		refreshAdvancedAccessibilityOfItem: function( itemToRefresh ) {
@@ -1723,7 +1729,7 @@
 			}
 			control.renderContent();
 			control.deferred.embedded.resolve(); // This triggers control.ready().
-			
+
 			// Mark all menu items as unprocessed.
 			$( 'button.item-edit' ).data( 'needs_accessibility_refresh', true );
 		},
@@ -1802,7 +1808,7 @@
 					control.moveRight();
 					control.params.depth += 1;
 				}
-				
+
 				moveBtn.focus(); // Re-focus after the container was moved.
 
 				// Mark all menu items as unprocessed.
@@ -2036,8 +2042,9 @@
 		},
 
 		/**
+		 * Gets the depth of the menu item.
 		 *
-		 * @return {number}
+		 * @return {number} The depth of the menu item.
 		 */
 		getDepth: function() {
 			var control = this, setting = control.setting(), depth = 0;
@@ -2103,7 +2110,9 @@
 		 **********************************************************************/
 
 		/**
-		 * @return {wp.customize.controlConstructor.nav_menu|null}
+		 * Gets the menu control that this menu item belongs to.
+		 *
+		 * @return {wp.customize.Menus.MenuControl|null} The menu control, or null if not found.
 		 */
 		getMenuControl: function() {
 			var control = this, settingValue = control.setting();
@@ -2127,9 +2136,9 @@
 		/**
 		 * @since 4.6.0
 		 *
-		 * @param {Boolean} expanded
+		 * @param {boolean} expanded
 		 * @param {Object} [params]
-		 * @return {Boolean} False if state already applied.
+		 * @return {boolean} False if state already applied.
 		 */
 		_toggleExpanded: api.Section.prototype._toggleExpanded,
 
@@ -2137,7 +2146,7 @@
 		 * @since 4.6.0
 		 *
 		 * @param {Object} [params]
-		 * @return {Boolean} False if already expanded.
+		 * @return {boolean} False if already expanded.
 		 */
 		expand: api.Section.prototype.expand,
 
@@ -2146,8 +2155,8 @@
 		 *
 		 * @since 4.5.0 Added params.completeCallback.
 		 *
-		 * @param {Object}   [params] - Optional params.
-		 * @param {Function} [params.completeCallback] - Function to call when the form toggle has finished animating.
+		 * @param {Object}   [params]                  Optional params.
+		 * @param {Function} [params.completeCallback] Function to call when the form toggle has finished animating.
 		 */
 		expandForm: function( params ) {
 			this.expand( params );
@@ -2157,7 +2166,7 @@
 		 * @since 4.6.0
 		 *
 		 * @param {Object} [params]
-		 * @return {Boolean} False if already collapsed.
+		 * @return {boolean} False if already collapsed.
 		 */
 		collapse: api.Section.prototype.collapse,
 
@@ -2166,8 +2175,8 @@
 		 *
 		 * @since 4.5.0 Added params.completeCallback.
 		 *
-		 * @param {Object}   [params] - Optional params.
-		 * @param {Function} [params.completeCallback] - Function to call when the form toggle has finished animating.
+		 * @param {Object}   [params]                  Optional params.
+		 * @param {Function} [params.completeCallback] Function to call when the form toggle has finished animating.
 		 */
 		collapseForm: function( params ) {
 			this.collapse( params );
@@ -2179,9 +2188,9 @@
 		 * @deprecated this is poor naming, and it is better to directly set control.expanded( showOrHide )
 		 * @since 4.5.0 Added params.completeCallback.
 		 *
-		 * @param {boolean}  [showOrHide] - If not supplied, will be inverse of current visibility
-		 * @param {Object}   [params] - Optional params.
-		 * @param {Function} [params.completeCallback] - Function to call when the form toggle has finished animating.
+		 * @param {boolean}  [showOrHide]              If not supplied, will be inverse of current visibility
+		 * @param {Object}   [params]                  Optional params.
+		 * @param {Function} [params.completeCallback] Function to call when the form toggle has finished animating.
 		 */
 		toggleForm: function( showOrHide, params ) {
 			if ( typeof showOrHide === 'undefined' ) {
@@ -2198,9 +2207,9 @@
 		 * Expand or collapse the menu item control.
 		 *
 		 * @since 4.6.0
-		 * @param {boolean}  [showOrHide] - If not supplied, will be inverse of current visibility
-		 * @param {Object}   [params] - Optional params.
-		 * @param {Function} [params.completeCallback] - Function to call when the form toggle has finished animating.
+		 * @param {boolean}  [showOrHide]              If not supplied, will be inverse of current visibility
+		 * @param {Object}   [params]                  Optional params.
+		 * @param {Function} [params.completeCallback] Function to call when the form toggle has finished animating.
 		 */
 		onChangeExpanded: function( showOrHide, params ) {
 			var self = this, $menuitem, $inside, complete;
@@ -2267,8 +2276,8 @@
 		 *
 		 * @since 4.5.0 Added params.completeCallback.
 		 *
-		 * @param {Object}   [params] - Params object.
-		 * @param {Function} [params.completeCallback] - Optional callback function when focus has completed.
+		 * @param {Object}   [params]                  Params object.
+		 * @param {Function} [params.completeCallback] Optional callback function when focus has completed.
 		 */
 		focus: function( params ) {
 			params = params || {};
@@ -2594,7 +2603,7 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {Object.<string,boolean>} selections - A map of location selections.
+		 * @param {Object.<string, boolean>} selections A map of location selections.
 		 * @return {void}
 		 */
 		setSelections: function( selections ) {
@@ -2781,7 +2790,7 @@
 		 * Notice that the UI aspects here are handled by wpNavMenu.initSortables()
 		 * which is called in MenuSection.onChangeExpanded()
 		 *
-		 * @param {Object} menuList - The element that has sortable().
+		 * @param {Object} menuList The element that has sortable().
 		 */
 		_setupSortable: function( menuList ) {
 			var control = this;
@@ -3019,7 +3028,9 @@
 		},
 
 		/**
-		 * @return {wp.customize.controlConstructor.nav_menu_item[]}
+		 * Get all of the nav_menu_item controls for this menu.
+		 *
+		 * @return {wp.customize.Menus.MenuItemControl[]} The nav_menu_item controls for this menu.
 		 */
 		getMenuItemControls: function() {
 			var menuControl = this,
@@ -3116,15 +3127,15 @@
 		 * has child items, this function will only be called once all of the
 		 * settings have been updated.
 		 */
-		debouncedReflowMenuItems: _.debounce( function() {
-			this.reflowMenuItems.apply( this, arguments );
+		debouncedReflowMenuItems: _.debounce( function( ...args ) {
+			this.reflowMenuItems.apply( this, args );
 		}, 0 ),
 
 		/**
 		 * Add a new item to this menu.
 		 *
-		 * @param {Object} item - Value for the nav_menu_item setting to be created.
-		 * @return {wp.customize.Menus.controlConstructor.nav_menu_item} The newly-created nav_menu_item control instance.
+		 * @param {Object} item Value for the nav_menu_item setting to be created.
+		 * @return {wp.customize.Menus.MenuItemControl} The newly-created nav_menu_item control instance.
 		 */
 		addItemToMenu: function( item ) {
 			var menuControl = this, customizeId, settingArgs, setting, menuItemControl, placeholderId, position = 0, priority = 10,
@@ -3189,7 +3200,9 @@
 		 *
 		 * @since 4.9.0
 		 *
-		 * @param {wp.customize.controlConstructor.nav_menu_item[]} optionalMenuItemControls
+		 * @param {wp.customize.Menus.MenuItemControl[]} [optionalMenuItemControls] The menu item controls to
+		 *                                                                        consider. Defaults to all of
+		 *                                                                        this menu's item controls.
 		 */
 		updateInvitationVisibility: function ( optionalMenuItemControls ) {
 			var menuItemControls = optionalMenuItemControls || this.getMenuItemControls();
@@ -3263,9 +3276,9 @@
 	 *
 	 * @alias wp.customize.Menus.applySavedData
 	 *
-	 * @param {Object} data
-	 * @param {Array} data.nav_menu_updates
-	 * @param {Array} data.nav_menu_item_updates
+	 * @param {Object}   data
+	 * @param {Object[]} data.nav_menu_updates
+	 * @param {Object[]} data.nav_menu_item_updates
 	 */
 	api.Menus.applySavedData = function( data ) {
 
@@ -3509,8 +3522,8 @@
 	 *
 	 * @alias wp.customize.Menus.getMenuControl
 	 *
-	 * @param menuId
-	 * @return {wp.customize.controlConstructor.menus[]}
+	 * @param {string|number} menuId The ID of the menu.
+	 * @return {wp.customize.Menus.MenuControl|undefined} The menu control, or undefined if not found.
 	 */
 	api.Menus.getMenuControl = function( menuId ) {
 		return api.control( 'nav_menu[' + menuId + ']' );
@@ -3521,8 +3534,8 @@
 	 *
 	 * @alias wp.customize.Menus.getMenuItemControl
 	 *
-	 * @param {string} menuItemId
-	 * @return {Object|null}
+	 * @param {string} menuItemId The ID of the menu item.
+	 * @return {wp.customize.Menus.MenuItemControl|undefined} The menu item control, or undefined if not found.
 	 */
 	api.Menus.getMenuItemControl = function( menuItemId ) {
 		return api.control( menuItemIdToSettingId( menuItemId ) );
@@ -3531,7 +3544,8 @@
 	/**
 	 * @alias wp.customize.Menus~menuItemIdToSettingId
 	 *
-	 * @param {string} menuItemId
+	 * @param {string} menuItemId The ID of the menu item.
+	 * @return {string} The setting ID for the menu item.
 	 */
 	function menuItemIdToSettingId( menuItemId ) {
 		return 'nav_menu_item[' + menuItemId + ']';
@@ -3543,8 +3557,8 @@
 	 *
 	 * @alias wp.customize.Menus~displayNavMenuName
 	 *
-	 * @param {string} name
-	 * @return {string}
+	 * @param {string} [name] The menu name.
+	 * @return {string} The sanitized display name, or a fallback "unnamed" string if empty.
 	 */
 	function displayNavMenuName( name ) {
 		name = name || '';
diff --git a/src/js/_enqueues/wp/customize/preview-nav-menus.js b/src/js/_enqueues/wp/customize/preview-nav-menus.js
index b5bec37b52aaf..b54d4e8a4f39d 100644
--- a/src/js/_enqueues/wp/customize/preview-nav-menus.js
+++ b/src/js/_enqueues/wp/customize/preview-nav-menus.js
@@ -5,6 +5,13 @@
 /* global _wpCustomizePreviewNavMenusExports */
 
 /** @namespace wp.customize.navMenusPreview */
+
+/**
+ * @param {JQueryStatic}       $   The jQuery object.
+ * @param {_.UnderscoreStatic} _   The Underscore.js object.
+ * @param {Object}             wp  The WordPress global object.
+ * @param {Object}             api The Customizer API.
+ */
 wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function( $, _, wp, api ) {
 	'use strict';
 
@@ -91,10 +98,10 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 			 * Constructor.
 			 *
 			 * @since 4.5.0
-			 * @param {string} id - Partial ID.
-			 * @param {Object} options
-			 * @param {Object} options.params
-			 * @param {Object} options.params.navMenuArgs
+			 * @param {string} id Partial ID.
+			 * @param {Object} [options]
+			 * @param {Object} [options.params]
+			 * @param {Object} [options.params.navMenuArgs]
 			 * @param {string} options.params.navMenuArgs.args_hmac
 			 * @param {string} [options.params.navMenuArgs.theme_location]
 			 * @param {number} [options.params.navMenuArgs.menu]
@@ -131,10 +138,10 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 			 * Return whether the setting is related to this partial.
 			 *
 			 * @since 4.5.0
-			 * @param {wp.customize.Value|string} setting  - Object or ID.
-			 * @param {number|Object|false|null}  newValue - New value, or null if the setting was just removed.
-			 * @param {number|Object|false|null}  oldValue - Old value, or null if the setting was just added.
-			 * @return {boolean}
+			 * @param {wp.customize.Value|string} setting  Object or ID.
+			 * @param {number|Object|false|null}  newValue New value, or null if the setting was just removed.
+			 * @param {number|Object|false|null}  oldValue Old value, or null if the setting was just added.
+			 * @return {boolean} True if the setting is related to this partial, false otherwise.
 			 */
 			isRelatedSetting: function( setting, newValue, oldValue ) {
 				var partial = this, navMenuLocationSetting, navMenuId, isNavMenuItemSetting, _newValue, _oldValue, urlParser;
@@ -210,7 +217,7 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 			 *
 			 * @since 4.5.0
 			 *
-			 * @return {Promise}
+			 * @return {Promise} A promise that is resolved when the refresh is complete, or rejected if the partial is no longer associated with a menu.
 			 */
 			refresh: function() {
 				var partial = this, menuId, deferred = $.Deferred();
@@ -263,7 +270,10 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 		/**
 		 * Request full refresh if there are nav menu instances that lack partials which also match the supplied args.
 		 *
-		 * @param {Object} navMenuInstanceArgs
+		 * @since 4.5.0
+		 *
+		 * @param {Object} navMenuInstanceArgs Arguments for a nav menu instance, which may include menu and/or theme_location.
+		 * @return {boolean} Whether a full refresh was requested.
 		 */
 		self.handleUnplacedNavMenuInstances = function( navMenuInstanceArgs ) {
 			var unplacedNavMenuInstances;
@@ -284,8 +294,8 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 		 *
 		 * @param {wp.customize.Value} setting
 		 * @param {Object}             [options]
-		 * @param {boolean}            options.fire Whether to invoke the callback after binding.
-		 *                                          This is used when a dynamic setting is added.
+		 * @param {boolean}            [options.fire] Whether to invoke the callback after binding.
+		 *                                            This is used when a dynamic setting is added.
 		 * @return {boolean} Whether the setting was bound.
 		 */
 		self.bindSettingListener = function( setting, options ) {
@@ -331,6 +341,7 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 		 * @since 4.5.0
 		 *
 		 * @param {wp.customize.Value} setting
+		 * @return {void}
 		 */
 		self.unbindSettingListener = function( setting ) {
 			setting.unbind( this.onChangeNavMenuSetting );
@@ -344,6 +355,7 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 		 * @since 4.5.0
 		 *
 		 * @this {wp.customize.Value}
+		 * @return {void}
 		 */
 		self.onChangeNavMenuSetting = function() {
 			var setting = this;
@@ -373,6 +385,7 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 		 * @param {Object} newItem New value for nav_menu_item[] setting.
 		 * @param {Object} oldItem Old value for nav_menu_item[] setting.
 		 * @this {wp.customize.Value}
+		 * @return {void}
 		 */
 		self.onChangeNavMenuItemSetting = function( newItem, oldItem ) {
 			var item = newItem || oldItem, navMenuSetting;
@@ -388,6 +401,7 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 		 * @since 4.5.0
 		 *
 		 * @this {wp.customize.Value}
+		 * @return {void}
 		 */
 		self.onChangeNavMenuLocationsSetting = function() {
 			var setting = this, hasNavMenuInstance;
@@ -412,6 +426,8 @@ wp.customize.navMenusPreview = wp.customize.MenusCustomizerPreview = ( function(
 	 * Also this applies even if a nav menu is not partial-refreshable.
 	 *
 	 * @since 4.5.0
+	 *
+	 * @return {void}
 	 */
 	self.highlightControls = function() {
 		var selector = '.menu-item';
diff --git a/src/js/_enqueues/wp/customize/preview-widgets.js b/src/js/_enqueues/wp/customize/preview-widgets.js
index e1191a65ad07f..487e294a93a29 100644
--- a/src/js/_enqueues/wp/customize/preview-widgets.js
+++ b/src/js/_enqueues/wp/customize/preview-widgets.js
@@ -11,10 +11,10 @@
  *
  * @namespace wp.customize.widgetsPreview
  *
- * @param {jQuery} $   The jQuery object.
- * @param {Object} _   The utilities library.
- * @param {Object} wp  Current WordPress environment instance.
- * @param {Object} api Information from the API.
+ * @param {JQueryStatic}       $   The jQuery object.
+ * @param {_.UnderscoreStatic} _   The Underscore.js object.
+ * @param {Object}             wp  The WordPress global object.
+ * @param {Object}             api The Customizer API.
  *
  * @return {Object} Widget-related variables.
  */
@@ -93,10 +93,9 @@ wp.customize.widgetsPreview = wp.customize.WidgetCustomizerPreview = (function(
 		 * @alias wp.customize.widgetsPreview.WidgetPartial
 		 * @memberOf wp.customize.widgetsPreview
 		 *
-		 * @param {string} id             The partial's ID.
-		 * @param {Object} options        Options used to initialize the partial's
-		 *                                instance.
-		 * @param {Object} options.params The options parameters.
+		 * @param {string} id               The partial's ID.
+		 * @param {Object} [options]        Options used to initialize the partial's instance.
+		 * @param {Object} [options.params] The options parameters.
 		 */
 		initialize: function( id, options ) {
 			var partial = this, matches;
@@ -170,9 +169,9 @@ wp.customize.widgetsPreview = wp.customize.WidgetCustomizerPreview = (function(
 		 * @memberOf wp.customize.widgetsPreview
 		 * @alias wp.customize.widgetsPreview.SidebarPartial
 		 *
-		 * @param {string} id             The partial's ID.
-		 * @param {Object} options        Options used to initialize the partial's instance.
-		 * @param {Object} options.params The options parameters.
+		 * @param {string} id               The partial's ID.
+		 * @param {Object} [options]        Options used to initialize the partial's instance.
+		 * @param {Object} [options.params] The options parameters.
 		 */
 		initialize: function( id, options ) {
 			var partial = this, matches;
@@ -293,8 +292,8 @@ wp.customize.widgetsPreview = wp.customize.WidgetCustomizerPreview = (function(
 		 *
 		 * @since 4.5.0
 		 *
-		 * @return {Array} An array containing placement objects for each of the
-		 *                 dynamic sidebar boundary nodes.
+		 * @return {wp.customize.selectiveRefresh.Placement[]} A placement for each of the dynamic
+		 *                                                     sidebar boundary nodes.
 		 */
 		placements: function() {
 			var partial = this;
@@ -320,7 +319,7 @@ wp.customize.widgetsPreview = wp.customize.WidgetCustomizerPreview = (function(
 		 * @throws {Error} If the setting doesn't exist in the API.
 		 * @throws {Error} If the API doesn't pass an array of widget IDs.
 		 *
-		 * @return {Array} A shallow copy of the array containing widget IDs.
+		 * @return {string[]} A shallow copy of the array containing widget IDs.
 		 */
 		getWidgetIds: function() {
 			var sidebarPartial = this, settingId, widgetIds;
@@ -344,7 +343,7 @@ wp.customize.widgetsPreview = wp.customize.WidgetCustomizerPreview = (function(
 		 *
 		 * @since 4.5.0
 		 *
-		 * @return {Array.<wp.customize.selectiveRefresh.Placement>} List of placements
+		 * @return {wp.customize.selectiveRefresh.Placement[]} List of placements
 		 *                                                           that were reflowed.
 		 */
 		reflowWidgets: function() {
@@ -477,8 +476,8 @@ wp.customize.widgetsPreview = wp.customize.WidgetCustomizerPreview = (function(
 		 *
 		 * @since 4.5.0
 		 *
-		 * @param {Array} newWidgetIds New widget IDs.
-		 * @param {Array} oldWidgetIds Old widget IDs.
+		 * @param {string[]} newWidgetIds New widget IDs.
+		 * @param {string[]} oldWidgetIds Old widget IDs.
 		 *
 		 * @return {void}
 		 */
diff --git a/src/js/_enqueues/wp/customize/preview.js b/src/js/_enqueues/wp/customize/preview.js
index 375cd2104ba0f..2830913f971a5 100644
--- a/src/js/_enqueues/wp/customize/preview.js
+++ b/src/js/_enqueues/wp/customize/preview.js
@@ -1,9 +1,14 @@
-/*
+/**
+ * @output wp-includes/js/customize-preview.js
+ */
+
+/**
  * Script run inside a Customizer preview frame.
  *
- * @output wp-includes/js/customize-preview.js
+ * @param {Object}       wp The WordPress global object.
+ * @param {JQueryStatic} $  The jQuery object.
  */
-(function( exports, $ ){
+(function( wp, $ ){
 	var api = wp.customize,
 		debounce,
 		currentHistoryState = {};
@@ -74,13 +79,16 @@
 	/**
 	 * Returns a debounced version of the function.
 	 *
+	 * @param {Function} fn        Function to debounce.
+	 * @param {number}   delay     Delay in milliseconds.
+	 * @param {Object}   [context] Context to invoke the function in. Defaults to the calling context.
 	 * @todo Require Underscore.js for this file and retire this.
+	 *
+	 * @return {Function} Debounced function.
 	 */
 	debounce = function( fn, delay, context ) {
 		var timeout;
-		return function() {
-			var args = arguments;
-
+		return function( ...args ) {
 			context = context || this;
 
 			clearTimeout( timeout );
@@ -95,15 +103,15 @@
 	 * @memberOf wp.customize
 	 * @alias wp.customize.Preview
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.customize.Messenger
 	 * @augments wp.customize.Class
 	 * @mixes wp.customize.Events
 	 */
 	api.Preview = api.Messenger.extend(/** @lends wp.customize.Preview.prototype */{
 		/**
-		 * @param {Object} params  - Parameters to configure the messenger.
-		 * @param {Object} options - Extend any instance parameter or method with this object.
+		 * @param {Object} params  Parameters to configure the messenger.
+		 * @param {Object} options Extend any instance parameter or method with this object.
 		 */
 		initialize: function( params, options ) {
 			var preview = this, urlParser = document.createElement( 'a' );
@@ -142,7 +150,8 @@
 		 * @since 4.7.0
 		 * @access public
 		 *
-		 * @param {jQuery.Event} event Event.
+		 * @param {JQuery.Event} event Event.
+		 * @return {void}
 		 */
 		handleLinkClick: function( event ) {
 			var preview = this, link, isInternalJumpLink;
@@ -188,7 +197,8 @@
 		 * @since 4.7.0
 		 * @access public
 		 *
-		 * @param {jQuery.Event} event Event.
+		 * @param {JQuery.Event} event Event.
+		 * @return {void}
 		 */
 		handleFormSubmit: function( event ) {
 			var preview = this, urlParser, form;
@@ -232,7 +242,6 @@
 	 *
 	 * @since 4.7.0
 	 * @access protected
-	 * @access private
 	 *
 	 * @return {void}
 	 */
@@ -714,9 +723,9 @@
 		/**
 		 * Create/update a setting value.
 		 *
-		 * @param {string}  id            - Setting ID.
-		 * @param {*}       value         - Setting value.
-		 * @param {boolean} [createDirty] - Whether to create a setting as dirty. Defaults to false.
+		 * @param {string}  id            Setting ID.
+		 * @param {*}       value         Setting value.
+		 * @param {boolean} [createDirty] Whether to create a setting as dirty. Defaults to false.
 		 */
 		setValue = function( id, value, createDirty ) {
 			var setting = api( id );
@@ -791,7 +800,7 @@
 		/**
 		 * Handle update to changeset UUID.
 		 *
-		 * @param {string} uuid - UUID.
+		 * @param {string} uuid UUID.
 		 * @return {void}
 		 */
 		handleUpdatedChangesetUuid = function( uuid ) {
@@ -888,8 +897,8 @@
 			return 'background_' + prop;
 		} );
 
-		api.when.apply( api, bg ).done( function() {
-			$.each( arguments, function() {
+		api.when.apply( api, bg ).done( function( ...settings ) {
+			$.each( settings, function() {
 				this.bind( api.settingPreviewHandlers.background );
 			});
 		});
diff --git a/src/js/_enqueues/wp/customize/selective-refresh.js b/src/js/_enqueues/wp/customize/selective-refresh.js
index 6744361066ce1..cacecfe53331a 100644
--- a/src/js/_enqueues/wp/customize/selective-refresh.js
+++ b/src/js/_enqueues/wp/customize/selective-refresh.js
@@ -5,6 +5,11 @@
 /* global jQuery, JSON, _customizePartialRefreshExports, console */
 
 /** @namespace wp.customize.selectiveRefresh */
+
+/**
+ * @param {JQueryStatic} $   The jQuery object.
+ * @param {Object}       api The Customizer API.
+ */
 wp.customize.selectiveRefresh = ( function( $, api ) {
 	'use strict';
 	var self, Partial, Placement;
@@ -37,7 +42,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 	 * @augments wp.customize.Class
 	 * @since 4.5.0
 	 */
-	Partial = self.Partial = api.Class.extend(/** @lends wp.customize.SelectiveRefresh.Partial.prototype */{
+	Partial = self.Partial = api.Class.extend(/** @lends wp.customize.selectiveRefresh.Partial.prototype */{
 
 		id: null,
 
@@ -45,7 +50,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * Default params.
 		 *
 		 * @since 4.9.0
-		 * @var {object}
+		 * @member {Object}
 		 */
 		defaults: {
 			selector: null,
@@ -59,14 +64,14 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 *
 		 * @since 4.5.0
 		 *
-		 * @param {string}  id                      - Unique identifier for the partial instance.
-		 * @param {Object}  options                 - Options hash for the partial instance.
-		 * @param {string}  options.type            - Type of partial (e.g. nav_menu, widget, etc)
-		 * @param {string}  options.selector        - jQuery selector to find the container element in the page.
-		 * @param {Array}   options.settings        - The IDs for the settings the partial relates to.
-		 * @param {string}  options.primarySetting  - The ID for the primary setting the partial renders.
-		 * @param {boolean} options.fallbackRefresh - Whether to refresh the entire preview in case of a partial refresh failure.
-		 * @param {Object}  [options.params]        - Deprecated wrapper for the above properties.
+		 * @param {string}   id                        Unique identifier for the partial instance.
+		 * @param {Object}   [options]                 Options hash for the partial instance.
+		 * @param {string}   [options.type]            Type of partial (e.g. nav_menu, widget, etc)
+		 * @param {string}   [options.selector]        jQuery selector to find the container element in the page.
+		 * @param {string[]} [options.settings]        The IDs for the settings the partial relates to.
+		 * @param {string}   [options.primarySetting]  The ID for the primary setting the partial renders.
+		 * @param {boolean}  [options.fallbackRefresh] Whether to refresh the entire preview in case of a partial refresh failure.
+		 * @param {Object}   [options.params]          Deprecated wrapper for the above properties.
 		 */
 		initialize: function( id, options ) {
 			var partial = this;
@@ -119,7 +124,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * @since 4.7.0
 		 * @access public
 		 *
-		 * @param {Placement} placement The placement container element.
+		 * @param {wp.customize.selectiveRefresh.Placement} placement The placement container element.
 		 * @return {void}
 		 */
 		createEditShortcutForPlacement: function( placement ) {
@@ -148,8 +153,8 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * @since 4.7.0
 		 * @access public
 		 *
-		 * @param {Placement} placement The placement for the partial.
-		 * @param {jQuery} $editShortcut The shortcut element as a jQuery object.
+		 * @param {wp.customize.selectiveRefresh.Placement} placement     The placement for the partial.
+		 * @param {jQuery}                                  $editShortcut The shortcut element as a jQuery object.
 		 * @return {void}
 		 */
 		addEditShortcutToPlacement: function( placement, $editShortcut ) {
@@ -253,7 +258,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 *
 		 * @since 4.5.0
 		 *
-		 * @return {Array.<Placement>}
+		 * @return {wp.customize.selectiveRefresh.Placement[]} The placements for this partial in the document.
 		 */
 		placements: function() {
 			var partial = this, selector;
@@ -285,7 +290,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 *
 		 * @since 4.5.0
 		 *
-		 * @return {string[]}
+		 * @return {string[]} The setting IDs related to this partial.
 		 */
 		settings: function() {
 			var partial = this;
@@ -344,7 +349,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 *
 		 * @since 4.5.0
 		 *
-		 * @param {Placement} placement
+		 * @param {wp.customize.selectiveRefresh.Placement} placement The placement to prepare.
 		 */
 		preparePlacement: function( placement ) {
 			$( placement.container ).addClass( 'customize-partial-refreshing' );
@@ -364,7 +369,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * @since 4.5.0
 		 *
 		 * @this {wp.customize.selectiveRefresh.Partial}
-		 * @return {jQuery.Promise}
+		 * @return {JQuery.Promise<*>} Promise for the request to render the partial.
 		 */
 		refresh: function() {
 			var partial = this, refreshPromise;
@@ -404,10 +409,10 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 *
 		 * @since 4.5.0
 		 *
-		 * @param {Placement}             placement
-		 * @param {Element|jQuery}        [placement.container]  - This param will be empty if there was no element matching the selector.
-		 * @param {string|Object|boolean} placement.addedContent - Rendered HTML content, a data object for JS templates to render, or false if no render.
-		 * @param {Object}                [placement.context]    - Optional context information about the container.
+		 * @param {wp.customize.selectiveRefresh.Placement} placement              The placement to render into.
+		 * @param {Element|jQuery}                          [placement.container]  This param will be empty if there was no element matching the selector.
+		 * @param {string|Object|boolean}                   placement.addedContent Rendered HTML content, a data object for JS templates to render, or false if no render.
+		 * @param {Object}                                  [placement.context]    Optional context information about the container.
 		 * @return {boolean} Whether the rendering was successful and the fallback was not invoked.
 		 */
 		renderContent: function( placement ) {
@@ -531,12 +536,12 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 	 * @augments wp.customize.Class
 	 * @since 4.5.0
 	 */
-	self.Placement = Placement = api.Class.extend(/** @lends wp.customize.selectiveRefresh.prototype */{
+	self.Placement = Placement = api.Class.extend(/** @lends wp.customize.selectiveRefresh.Placement.prototype */{
 
 		/**
 		 * The partial with which the container is associated.
 		 *
-		 * @param {wp.customize.selectiveRefresh.Partial}
+		 * @member {wp.customize.selectiveRefresh.Partial}
 		 */
 		partial: null,
 
@@ -547,6 +552,8 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * DOM element, such as in the case of a sidebar partial.
 		 * This container element itself will be replaced for partials that
 		 * have containerInclusive param defined as true.
+		 *
+		 * @member {jQuery}
 		 */
 		container: null,
 
@@ -556,6 +563,8 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * This will normally be the same as endNode since most placements appear as elements.
 		 * This is primarily useful for widget sidebars which do not have intrinsic containers, but
 		 * for which an HTML comment is output before to mark the starting position.
+		 *
+		 * @member {Node}
 		 */
 		startNode: null,
 
@@ -565,6 +574,8 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * This will normally be the same as startNode since most placements appear as elements.
 		 * This is primarily useful for widget sidebars which do not have intrinsic containers, but
 		 * for which an HTML comment is output before to mark the ending position.
+		 *
+		 * @member {Node}
 		 */
 		endNode: null,
 
@@ -574,14 +585,14 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * This provides information about the placement which is included in the request
 		 * in order to render the partial properly.
 		 *
-		 * @param {object}
+		 * @member {Object}
 		 */
 		context: null,
 
 		/**
 		 * The content for the partial when refreshed.
 		 *
-		 * @param {string}
+		 * @member {string|Object|boolean}
 		 */
 		addedContent: null,
 
@@ -589,11 +600,11 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 * DOM node(s) removed when the partial is refreshed.
 		 *
 		 * If the partial is containerInclusive, then the removedNodes will be
-		 * the single Element that was the partial's former placement. If the
+		 * the jQuery object for the partial's former placement. If the
 		 * partial is not containerInclusive, then the removedNodes will be a
-		 * documentFragment containing the nodes removed.
+		 * DocumentFragment containing the nodes removed.
 		 *
-		 * @param {Element|DocumentFragment}
+		 * @member {jQuery|DocumentFragment}
 		 */
 		removedNodes: null,
 
@@ -602,14 +613,14 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		 *
 		 * @since 4.5.0
 		 *
-		 * @param {Object}                   args
-		 * @param {Partial}                  args.partial
-		 * @param {jQuery|Element}           [args.container]
-		 * @param {Node}                     [args.startNode]
-		 * @param {Node}                     [args.endNode]
-		 * @param {Object}                   [args.context]
-		 * @param {string}                   [args.addedContent]
-		 * @param {jQuery|DocumentFragment}  [args.removedNodes]
+		 * @param {Object}                                args                The placement properties.
+		 * @param {wp.customize.selectiveRefresh.Partial} args.partial        The partial with which the container is associated.
+		 * @param {jQuery|Element}                        [args.container]    DOM element which contains the placement's contents.
+		 * @param {Node}                                  [args.startNode]    DOM node for the initial boundary of the placement.
+		 * @param {Node}                                  [args.endNode]      DOM node for the terminal boundary of the placement.
+		 * @param {Object}                                [args.context]      Context data included in the request in order to render the partial.
+		 * @param {string|Object|boolean}                 [args.addedContent] The content for the partial when refreshed.
+		 * @param {jQuery|DocumentFragment}               [args.removedNodes] DOM node(s) removed when the partial is refreshed.
 		 */
 		initialize: function( args ) {
 			var placement = this;
@@ -645,7 +656,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 	 * @since 4.5.0
 	 * @see wp.customize.previewer.query()
 	 *
-	 * @return {Object}
+	 * @return {Object} POST vars for a Customizer preview request.
 	 */
 	self.getCustomizeQuery = function() {
 		var dirtyCustomized = {};
@@ -668,7 +679,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 	 * Currently-requested partials and their associated deferreds.
 	 *
 	 * @since 4.5.0
-	 * @type {Object<string, { deferred: jQuery.Promise, partial: wp.customize.selectiveRefresh.Partial }>}
+	 * @type {Object.<string, { deferred: JQuery.Promise<*>, partial: wp.customize.selectiveRefresh.Partial }>}
 	 */
 	self._pendingPartialRequests = {};
 
@@ -685,7 +696,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 	 * Current jqXHR for the request to the partials.
 	 *
 	 * @since 4.5.0
-	 * @type {jQuery.jqXHR|null}
+	 * @type {JQuery.jqXHR|null}
 	 * @private
 	 */
 	self._currentRequest = null;
@@ -708,7 +719,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 	 * @since 4.5.0
 	 *
 	 * @param {wp.customize.selectiveRefresh.Partial} partial
-	 * @return {jQuery.Promise}
+	 * @return {JQuery.Promise<*>} Promise for the request to render the partial.
 	 */
 	self.requestPartial = function( partial ) {
 		var partialRequest;
@@ -856,9 +867,9 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 	 *
 	 * @since 4.5.0
 	 *
-	 * @param {jQuery|HTMLElement} [rootElement]
-	 * @param {object}             [options]
-	 * @param {boolean=true}       [options.triggerRendered]
+	 * @param {jQuery|HTMLElement} [rootElement]                  Element to scan for partials. Defaults to the document element.
+	 * @param {Object}             [options]                      Options.
+	 * @param {boolean}            [options.triggerRendered=true] Whether to trigger the rendered event for the placements found.
 	 */
 	self.addPartials = function( rootElement, options ) {
 		var containerElements;
@@ -1016,7 +1027,7 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		/**
 		 * Handle rendering of partials.
 		 *
-		 * @param {api.selectiveRefresh.Placement} placement
+		 * @param {wp.customize.selectiveRefresh.Placement} placement
 		 */
 		api.selectiveRefresh.bind( 'partial-content-rendered', function( placement ) {
 			if ( placement.container ) {
@@ -1027,8 +1038,8 @@ wp.customize.selectiveRefresh = ( function( $, api ) {
 		/**
 		 * Handle setting validities in partial refresh response.
 		 *
-		 * @param {object} data Response data.
-		 * @param {object} data.setting_validities Setting validities.
+		 * @param {Object} data Response data.
+		 * @param {Object} data.setting_validities Setting validities.
 		 */
 		api.selectiveRefresh.bind( 'render-partials-response', function handleSettingValiditiesResponse( data ) {
 			if ( data.setting_validities ) {
diff --git a/src/js/_enqueues/wp/customize/views.js b/src/js/_enqueues/wp/customize/views.js
index 02c984de70c43..e945b54348d8b 100644
--- a/src/js/_enqueues/wp/customize/views.js
+++ b/src/js/_enqueues/wp/customize/views.js
@@ -2,6 +2,11 @@
  * @output wp-includes/js/customize-views.js
  */
 
+/**
+ * @param {JQueryStatic}       $  The jQuery object.
+ * @param {Object}             wp The WordPress global object.
+ * @param {_.UnderscoreStatic} _  The Underscore.js object.
+ */
 (function( $, wp, _ ) {
 
 	if ( ! wp || ! wp.customize ) { return; }
@@ -18,23 +23,34 @@
 	 * @memberOf wp.customize.HeaderTool
 	 * @alias wp.customize.HeaderTool.CurrentView
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.Backbone.View
 	 */
 	api.HeaderTool.CurrentView = wp.Backbone.View.extend(/** @lends wp.customize.HeaderTool.CurrentView.prototype */{
 		template: wp.template('header-current'),
 
+		/**
+		 * Initialize.
+		 */
 		initialize: function() {
 			this.listenTo(this.model, 'change', this.render);
 			this.render();
 		},
 
+		/**
+		 * Render.
+		 *
+		 * @return {wp.customize.HeaderTool.CurrentView} Current view.
+		 */
 		render: function() {
 			this.$el.html(this.template(this.model.toJSON()));
 			this.setButtons();
 			return this;
 		},
 
+		/**
+		 * Set buttons.
+		 */
 		setButtons: function() {
 			var elements = $('#customize-control-header_image .actions .remove');
 			var addButton = $('#customize-control-header_image .actions .new');
@@ -64,7 +80,7 @@
 	 * @memberOf wp.customize.HeaderTool
 	 * @alias wp.customize.HeaderTool.ChoiceView
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.Backbone.View
 	 */
 	api.HeaderTool.ChoiceView = wp.Backbone.View.extend(/** @lends wp.customize.HeaderTool.ChoiceView.prototype */{
@@ -77,6 +93,9 @@
 			'click .close': 'removeImage'
 		},
 
+		/**
+		 * Initialize.
+		 */
 		initialize: function() {
 			var properties = [
 				this.model.get('header').url,
@@ -90,6 +109,11 @@
 			}
 		},
 
+		/**
+		 * Render.
+		 *
+		 * @return {wp.customize.HeaderTool.ChoiceView} Choice view.
+		 */
 		render: function() {
 			this.$el.html(this.template(this.extendedModel()));
 
@@ -97,10 +121,18 @@
 			return this;
 		},
 
+		/**
+		 * Toggle selected.
+		 */
 		toggleSelected: function() {
 			this.$el.toggleClass('selected', this.model.get('selected'));
 		},
 
+		/**
+		 * Extended model.
+		 *
+		 * @return {Object} Extended model.
+		 */
 		extendedModel: function() {
 			var c = this.model.get('collection');
 			return _.extend(this.model.toJSON(), {
@@ -108,12 +140,18 @@
 			});
 		},
 
+		/**
+		 * Select.
+		 */
 		select: function() {
 			this.preventJump();
 			this.model.save();
 			api.HeaderTool.currentHeader.set(this.extendedModel());
 		},
 
+		/**
+		 * Prevent jump.
+		 */
 		preventJump: function() {
 			var container = $('.wp-full-overlay-sidebar-content'),
 				scroll = container.scrollTop();
@@ -123,6 +161,11 @@
 			});
 		},
 
+		/**
+		 * Remove image.
+		 *
+		 * @param {Event} e Event.
+		 */
 		removeImage: function(e) {
 			e.stopPropagation();
 			this.model.destroy();
@@ -142,10 +185,13 @@
 	 * @memberOf wp.customize.HeaderTool
 	 * @alias wp.customize.HeaderTool.ChoiceListView
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.Backbone.View
 	 */
 	api.HeaderTool.ChoiceListView = wp.Backbone.View.extend(/** @lends wp.customize.HeaderTool.ChoiceListView.prototype */{
+		/**
+		 * Initialize.
+		 */
 		initialize: function() {
 			this.listenTo(this.collection, 'add', this.addOne);
 			this.listenTo(this.collection, 'remove', this.render);
@@ -154,12 +200,23 @@
 			this.render();
 		},
 
+		/**
+		 * Render.
+		 *
+		 * @return {wp.customize.HeaderTool.ChoiceListView} Choice list view.
+		 */
 		render: function() {
 			this.$el.empty();
 			this.collection.each(this.addOne, this);
 			this.toggleList();
+			return this;
 		},
 
+		/**
+		 * Add one.
+		 *
+		 * @param {Backbone.Model} choice Choice.
+		 */
 		addOne: function(choice) {
 			var view;
 			choice.set({ collection: this.collection });
@@ -167,6 +224,9 @@
 			this.$el.append(view.render().el);
 		},
 
+		/**
+		 * Toggle list.
+		 */
 		toggleList: function() {
 			var title = this.$el.parents().prev('.customize-control-title'),
 				randomButton = this.$el.find('.random').parent();
@@ -188,14 +248,26 @@
 	 * @memberOf wp.customize.HeaderTool
 	 * @alias wp.customize.HeaderTool.CombinedList
 	 *
-	 * @constructor
+	 * @class
 	 * @augments wp.Backbone.View
 	 */
 	api.HeaderTool.CombinedList = wp.Backbone.View.extend(/** @lends wp.customize.HeaderTool.CombinedList.prototype */{
+		/**
+		 * Initialize.
+		 *
+		 * @param {Backbone.Collection[]} collections Collections.
+		 */
 		initialize: function(collections) {
 			this.collections = collections;
 			this.on('all', this.propagate, this);
 		},
+
+		/**
+		 * Propagate event.
+		 *
+		 * @param {string} event Event.
+		 * @param {*}      arg   Argument.
+		 */
 		propagate: function(event, arg) {
 			_.each(this.collections, function(collection) {
 				collection.trigger(event, arg);
diff --git a/src/js/_enqueues/wp/customize/widgets.js b/src/js/_enqueues/wp/customize/widgets.js
index 56459ad7452e1..999883f5fb3b6 100644
--- a/src/js/_enqueues/wp/customize/widgets.js
+++ b/src/js/_enqueues/wp/customize/widgets.js
@@ -3,6 +3,11 @@
  */
 
 /* global _wpCustomizeWidgetsSettings */
+
+/**
+ * @param {Object}       wp The WordPress global object.
+ * @param {JQueryStatic} $  The jQuery object.
+ */
 (function( wp, $ ){
 
 	if ( ! wp || ! wp.customize ) { return; }
@@ -251,7 +256,7 @@
 
 		/**
 		 * Updates the count of the available widgets that have the `search_matched` attribute.
- 		 */
+		 */
 		updateSearchMatchesCount: function() {
 			this.searchMatchesCount = this.collection.where({ search_matched: true }).length;
 		},
@@ -271,7 +276,7 @@
 
 		/**
 		 * Changes visibility of available widgets.
- 		 */
+		 */
 		updateList: function() {
 			this.collection.each( function( widget ) {
 				var widgetTpl = $( '#widget-tpl-' + widget.id );
@@ -284,7 +289,9 @@
 
 		/**
 		 * Highlights a widget.
- 		 */
+		 *
+		 * @param {jQuery} widgetTpl The widget template to highlight.
+		 */
 		select: function( widgetTpl ) {
 			this.selected = $( widgetTpl );
 			this.selected.siblings( '.widget-tpl' ).removeClass( 'selected' );
@@ -293,6 +300,8 @@
 
 		/**
 		 * Highlights a widget on focus.
+		 *
+		 * @param {JQuery.Event} event The focus event.
 		 */
 		focus: function( event ) {
 			this.select( $( event.currentTarget ) );
@@ -300,6 +309,8 @@
 
 		/**
 		 * Handles submit for keypress and click on widget.
+		 *
+		 * @param {JQuery.Event} event The keypress or click event.
 		 */
 		_submit: function( event ) {
 			// Only proceed with keypress if it is Enter or Spacebar.
@@ -312,7 +323,9 @@
 
 		/**
 		 * Adds a selected widget to the sidebar.
- 		 */
+		 *
+		 * @param {jQuery} widgetTpl The widget template to add.
+		 */
 		submit: function( widgetTpl ) {
 			var widgetId, widget, widgetFormControl;
 
@@ -342,6 +355,8 @@
 
 		/**
 		 * Opens the panel.
+		 *
+		 * @param {wp.customize.Widgets.SidebarControl} sidebarControl The sidebar control that opened the panel.
 		 */
 		open: function( sidebarControl ) {
 			this.currentSidebarControl = sidebarControl;
@@ -371,6 +386,8 @@
 
 		/**
 		 * Closes the panel.
+		 *
+		 * @param {Object} [options] Options for closing the panel.
 		 */
 		close: function( options ) {
 			options = options || {};
@@ -389,6 +406,8 @@
 
 		/**
 		 * Adds keyboard accessibility to the panel.
+		 *
+		 * @param {JQuery.Event} event The keydown event.
 		 */
 		keyboardAccessible: function( event ) {
 			var isEnter = ( event.which === 13 ),
@@ -457,7 +476,7 @@
 	api.Widgets.formSyncHandlers = {
 
 		/**
-		 * @param {jQuery.Event} e
+		 * @param {JQuery.Event} e
 		 * @param {jQuery} widget
 		 * @param {string} newForm
 		 */
@@ -491,6 +510,9 @@
 		 *
 		 * @constructs wp.customize.Widgets.WidgetControl
 		 * @augments   wp.customize.Control
+		 *
+		 * @param {string} id      Control ID.
+		 * @param {Object} options Control options.
 		 */
 		initialize: function( id, options ) {
 			var control = this;
@@ -953,9 +975,9 @@
 
 			formSyncHandler = api.Widgets.formSyncHandlers[ this.params.widget_id_base ];
 			if ( formSyncHandler ) {
-				$( document ).on( 'widget-synced', function( e, widget ) {
+				$( document ).on( 'widget-synced', function( e, widget, ...args ) {
 					if ( $widgetRoot.is( widget ) ) {
-						formSyncHandler.apply( document, arguments );
+						formSyncHandler.call( document, e, widget, ...args );
 					}
 				} );
 			}
@@ -968,9 +990,9 @@
 		 *
 		 * @since 4.1.0
 		 *
-		 * @param {boolean}   active
-		 * @param {Object}    args
-		 * @param {function}  args.completeCallback
+		 * @param {boolean}  active                Whether the widget is rendered.
+		 * @param {Object}   args                  Args.
+		 * @param {Function} args.completeCallback Function to call once the class has been toggled.
 		 */
 		onChangeActive: function ( active, args ) {
 			// Note: there is a second 'args' parameter being passed, merged on top of this.defaultActiveArguments.
@@ -1052,7 +1074,7 @@
 		 * This string can be used to compare whether or not the form has all of the same fields.
 		 *
 		 * @param {jQuery} inputs
-		 * @return {string}
+		 * @return {string} Signature string for the inputs.
 		 * @private
 		 */
 		_getInputsSignature: function( inputs ) {
@@ -1075,7 +1097,7 @@
 		 * Get the state for an input depending on its type.
 		 *
 		 * @param {jQuery|Element} input
-		 * @return {string|boolean|Array|*}
+		 * @return {string|boolean|string[]|*} State of the input.
 		 * @private
 		 */
 		_getInputState: function( input ) {
@@ -1095,7 +1117,7 @@
 		 * Update an input's state based on its type.
 		 *
 		 * @param {jQuery|Element} input
-		 * @param {string|boolean|Array|*} state
+		 * @param {string|boolean|string[]|*} state
 		 * @private
 		 */
 		_setInputState: function ( input, state ) {
@@ -1124,7 +1146,9 @@
 		 **********************************************************************/
 
 		/**
-		 * @return {wp.customize.controlConstructor.sidebar_widgets[]}
+		 * Get the sidebar widgets control for the sidebar this widget is in.
+		 *
+		 * @return {wp.customize.Widgets.SidebarControl|undefined} The sidebar widgets control, or undefined if not found.
 		 */
 		getSidebarWidgetsControl: function() {
 			var settingId, sidebarWidgetsControl;
@@ -1341,9 +1365,9 @@
 		/**
 		 * @since 4.1.0
 		 *
-		 * @param {Boolean} expanded
+		 * @param {boolean} expanded
 		 * @param {Object} [params]
-		 * @return {Boolean} False if state already applied.
+		 * @return {boolean} False if state already applied.
 		 */
 		_toggleExpanded: api.Section.prototype._toggleExpanded,
 
@@ -1351,7 +1375,7 @@
 		 * @since 4.1.0
 		 *
 		 * @param {Object} [params]
-		 * @return {Boolean} False if already expanded.
+		 * @return {boolean} False if already expanded.
 		 */
 		expand: api.Section.prototype.expand,
 
@@ -1368,7 +1392,7 @@
 		 * @since 4.1.0
 		 *
 		 * @param {Object} [params]
-		 * @return {Boolean} False if already collapsed.
+		 * @return {boolean} False if already collapsed.
 		 */
 		collapse: api.Section.prototype.collapse,
 
@@ -1498,7 +1522,7 @@
 		/**
 		 * Get the position (index) of the widget in the containing sidebar
 		 *
-		 * @return {number}
+		 * @return {number|void} Index of the widget in the sidebar, or undefined if not found
 		 */
 		getWidgetSidebarPosition: function() {
 			var sidebarWidgetIds, position;
@@ -1642,7 +1666,7 @@
 				/**
 				 * Determine whether or not the notice should be displayed.
 				 *
-				 * @return {boolean}
+				 * @return {boolean} True if the notice should be displayed, false otherwise.
 				 */
 				shouldShowNotice = function() {
 					var activeSectionCount = getActiveSectionCount();
@@ -1712,7 +1736,7 @@
 		 *
 		 * @since 4.4.0
 		 *
-		 * @return {boolean}
+		 * @return {boolean} True if the panel is contextually active, false otherwise.
 		 */
 		isContextuallyActive: function() {
 			var panel = this;
@@ -2048,7 +2072,7 @@
 		 * Get the widget_form Customize controls associated with the current sidebar.
 		 *
 		 * @since 3.9.0
-		 * @return {wp.customize.controlConstructor.widget_form[]}
+		 * @return {wp.customize.Widgets.WidgetControl[]} Widget form controls associated with the current sidebar.
 		 */
 		getWidgetFormControls: function() {
 			var formControls = [];
@@ -2065,8 +2089,10 @@
 		},
 
 		/**
-		 * @param {string} widgetId or an id_base for adding a previously non-existing widget.
-		 * @return {Object|false} widget_form control instance, or false on error.
+		 * Add a widget to the sidebar.
+		 *
+		 * @param {string} widgetId Widget ID, or an id_base for adding a previously non-existing widget.
+		 * @return {wp.customize.Widgets.WidgetControl|false} The widget_form control instance, or false on error.
 		 */
 		addWidget: function( widgetId ) {
 			var self = this, controlHtml, $widget, controlType = 'widget_form', controlContainer, controlConstructor,
@@ -2247,7 +2273,7 @@
 	/**
 	 * Given a widget control, find the sidebar widgets control that contains it.
 	 * @param {string} widgetId
-	 * @return {Object|null}
+	 * @return {Object|null} Sidebar widgets control that contains the widget, or null if not found.
 	 */
 	api.Widgets.getSidebarWidgetControlContainingWidget = function( widgetId ) {
 		var foundControl = null;
@@ -2266,7 +2292,7 @@
 	 * Given a widget ID for a widget appearing in the preview, get the widget form control associated with it.
 	 *
 	 * @param {string} widgetId
-	 * @return {Object|null}
+	 * @return {Object|null} Widget form control associated with the widget, or null if not found.
 	 */
 	api.Widgets.getWidgetFormControlForWidget = function( widgetId ) {
 		var foundControl = null;
@@ -2319,8 +2345,8 @@
 	 *
 	 * This overrides the back button to serve the purpose of breadcrumb navigation.
 	 *
-	 * @param {wp.customize.Section|wp.customize.Panel|wp.customize.Control} focusConstruct - The object to initially focus.
-	 * @param {wp.customize.Section|wp.customize.Panel|wp.customize.Control} returnConstruct - The object to return focus.
+	 * @param {wp.customize.Section|wp.customize.Panel|wp.customize.Control} focusConstruct  The object to initially focus.
+	 * @param {wp.customize.Section|wp.customize.Panel|wp.customize.Control} returnConstruct The object to return focus.
 	 */
 	function focusConstructWithBreadcrumb( focusConstruct, returnConstruct ) {
 		focusConstruct.focus();
@@ -2335,7 +2361,7 @@
 
 	/**
 	 * @param {string} widgetId
-	 * @return {Object}
+	 * @return {Object} Parsed widget ID with id_base and number properties
 	 */
 	function parseWidgetId( widgetId ) {
 		var matches, parsed = {
diff --git a/tests/qunit/wp-admin/js/customize-base.js b/tests/qunit/wp-admin/js/customize-base.js
index bd3535b3bc3b0..0d093321f81ef 100644
--- a/tests/qunit/wp-admin/js/customize-base.js
+++ b/tests/qunit/wp-admin/js/customize-base.js
@@ -2,6 +2,7 @@
 
 jQuery( function( $ ) {
 	var FooSuperClass, BarSubClass, foo, bar, ConstructorTestClass, newConstructor, constructorTest, $mockElement, mockString,
+	ApplicatorTestClass, ArityTestClass,
 	firstInitialValue, firstValueInstance, valuesInstance, wasCallbackFired, mockValueCallback;
 
 	QUnit.module( 'Customize Base: Class' );
@@ -47,8 +48,64 @@ jQuery( function( $ ) {
 		assert.equal( foo.instanceProp, 'instancePropValue' );
 	});
 
-	// @todo Test Class.applicator?
-	// @todo Do we test object.instance?
+	ApplicatorTestClass = wp.customize.Class.extend({
+		initialize: function( firstArg, secondArg ) {
+			this.firstArg = firstArg;
+			this.secondArg = secondArg;
+
+			// The instance is extended before initialize() runs.
+			this.hadExtraPropDuringInitialize = ( 'extraPropValue' === this.extraProp );
+		}
+	});
+	QUnit.test( 'Class.applicator supplies the array as the initialize() arguments', function( assert ) {
+		var applicatorTest = new ApplicatorTestClass(
+			wp.customize.Class.applicator,
+			[ 'firstArgValue', 'secondArgValue' ]
+		);
+		assert.equal( applicatorTest.firstArg, 'firstArgValue' );
+		assert.equal( applicatorTest.secondArg, 'secondArgValue' );
+	});
+	QUnit.test( 'Class.applicator extends the instance before initialize() runs', function( assert ) {
+		var applicatorTest = new ApplicatorTestClass(
+			wp.customize.Class.applicator,
+			[ 'firstArgValue' ],
+			{ extraProp: 'extraPropValue' }
+		);
+		assert.equal( applicatorTest.firstArg, 'firstArgValue' );
+		assert.equal( applicatorTest.extraProp, 'extraPropValue' );
+		assert.ok( applicatorTest.hadExtraPropDuringInitialize );
+	});
+
+	ArityTestClass = wp.customize.Class.extend({
+		initialize: function( ...initializeArgs ) {
+			this.initializeArgCount = initializeArgs.length;
+		}
+	});
+	QUnit.test( 'Class supplies initialize() with exactly the arguments it was given', function( assert ) {
+		assert.equal( ( new ArityTestClass() ).initializeArgCount, 0 );
+		assert.equal( ( new ArityTestClass( 'a' ) ).initializeArgCount, 1 );
+		assert.equal( ( new ArityTestClass( 'a', 'b' ) ).initializeArgCount, 2 );
+		assert.equal( ( new ArityTestClass( 'a', 'b', 'c' ) ).initializeArgCount, 3 );
+		assert.equal( ( new ArityTestClass( 'a', 'b', 'c', 'd' ) ).initializeArgCount, 4 );
+
+		// The applicator form supplies the arguments as an array instead.
+		assert.equal(
+			( new ArityTestClass( wp.customize.Class.applicator, [ 'a', 'b' ] ) ).initializeArgCount,
+			2
+		);
+	});
+
+	QUnit.test( 'Class instance with an instance() method is callable as a function', function( assert ) {
+		var instanceTest = new wp.customize.Value( 'initialValue' );
+
+		// Calling with no arguments delegates to get().
+		assert.equal( instanceTest(), 'initialValue' );
+
+		// Calling with arguments delegates to set().
+		instanceTest( 'updatedValue' );
+		assert.equal( instanceTest.get(), 'updatedValue' );
+		assert.equal( instanceTest(), 'updatedValue' );
+	});
 
 	QUnit.module( 'Customize Base: Subclass' );
 
@@ -159,6 +216,73 @@ jQuery( function( $ ) {
 		assert.ok( wasCallbackFired );
 	});
 
+	QUnit.test( '.bind() and .unbind() accept multiple callbacks', function( assert ) {
+		var value = new wp.customize.Value( 'firstValue' ),
+			firstCallbackCount = 0,
+			secondCallbackCount = 0,
+			firstCallback = function() {
+				firstCallbackCount++;
+			},
+			secondCallback = function() {
+				secondCallbackCount++;
+			};
+
+		value.bind( firstCallback, secondCallback );
+		value.set( 'secondValue' );
+		assert.equal( firstCallbackCount, 1 );
+		assert.equal( secondCallbackCount, 1 );
+
+		value.unbind( firstCallback, secondCallback );
+		value.set( 'thirdValue' );
+		assert.equal( firstCallbackCount, 1, 'First callback no longer fires once unbound.' );
+		assert.equal( secondCallbackCount, 1, 'Second callback no longer fires once unbound.' );
+	});
+
+	QUnit.test( '.link() follows multiple values, and .unlink() stops following them', function( assert ) {
+		var follower = new wp.customize.Value( 'followerValue' ),
+			firstLeader = new wp.customize.Value( 'firstLeaderValue' ),
+			secondLeader = new wp.customize.Value( 'secondLeaderValue' );
+
+		follower.link( firstLeader, secondLeader );
+
+		firstLeader.set( 'firstLeaderUpdated' );
+		assert.equal( follower.get(), 'firstLeaderUpdated' );
+
+		secondLeader.set( 'secondLeaderUpdated' );
+		assert.equal( follower.get(), 'secondLeaderUpdated' );
+
+		// Linking is one-directional, so the leaders do not follow the follower.
+		follower.set( 'followerUpdated' );
+		assert.equal( firstLeader.get(), 'firstLeaderUpdated' );
+		assert.equal( secondLeader.get(), 'secondLeaderUpdated' );
+
+		follower.unlink( firstLeader, secondLeader );
+		firstLeader.set( 'firstLeaderUpdatedAgain' );
+		secondLeader.set( 'secondLeaderUpdatedAgain' );
+		assert.equal( follower.get(), 'followerUpdated', 'Value stops following once unlinked.' );
+	});
+
+	QUnit.test( '.sync() keeps values updated in both directions, and .unsync() stops them', function( assert ) {
+		var first = new wp.customize.Value( 'firstValue' ),
+			second = new wp.customize.Value( 'secondValue' );
+
+		first.sync( second );
+
+		second.set( 'setOnSecond' );
+		assert.equal( first.get(), 'setOnSecond' );
+
+		first.set( 'setOnFirst' );
+		assert.equal( second.get(), 'setOnFirst' );
+
+		first.unsync( second );
+
+		// Both directions have to stop, so check each of them.
+		second.set( 'setOnSecondAgain' );
+		assert.equal( first.get(), 'setOnFirst', 'First value stops following the second once unsynced.' );
+		first.set( 'setOnFirstAgain' );
+		assert.equal( second.get(), 'setOnSecondAgain', 'Second value stops following the first once unsynced.' );
+	});
+
 	QUnit.module( 'Customize Base: Values Class' );
 
 	valuesInstance = new wp.customize.Values();
@@ -205,6 +329,44 @@ jQuery( function( $ ) {
 		assert.ok( ! wasEventFiredOnRemoval );
 	});
 
+	QUnit.test( '.create() passes the extra arguments to the new value\'s initialize()', function( assert ) {
+		var collection = new wp.customize.Values();
+
+		collection.create( 'createdValue', 'suppliedInitialValue', { extraProp: 'extraPropValue' } );
+
+		assert.ok( collection.has( 'createdValue' ) );
+		assert.equal( collection( 'createdValue' ).get(), 'suppliedInitialValue' );
+		assert.equal( collection( 'createdValue' ).extraProp, 'extraPropValue' );
+	});
+
+	QUnit.test( '.when() invokes the callback once every requested value exists', function( assert ) {
+		var collection = new wp.customize.Values(),
+			passedValues = null;
+
+		collection.add( 'existingValue', new wp.customize.Value( 'existingValueContents' ) );
+
+		collection.when( 'existingValue', 'pendingValue', function( existingValue, pendingValue ) {
+			passedValues = [ existingValue.get(), pendingValue.get() ];
+		} );
+
+		assert.equal( passedValues, null, 'Callback waits for the value that does not exist yet.' );
+
+		collection.add( 'pendingValue', new wp.customize.Value( 'pendingValueContents' ) );
+
+		/*
+		 * The promise returned by when() resolves by way of a timer, and this
+		 * suite wraps every test with sinon's fake timers, so the clock has to
+		 * be advanced before the callback runs.
+		 */
+		this.clock.tick( 10 );
+
+		assert.deepEqual(
+			passedValues,
+			[ 'existingValueContents', 'pendingValueContents' ],
+			'Callback is invoked with every requested value.'
+		);
+	});
+
 	QUnit.module( 'Customize Base: Notification' );
 	QUnit.test( 'Notification object exists and has expected properties', function ( assert ) {
 		var notification = new wp.customize.Notification( 'mycode', {