WordPress 4.5
[autoinstalls/wordpress.git] / wp-includes / class-wp-customize-widgets.php
index 728bb5f04b12bec14ef85ab55d5525033fb81cd0..0a73953167b47d8afbe45d8bd40164bf4d3d9845 100644 (file)
@@ -61,6 +61,15 @@ final class WP_Customize_Widgets {
         */
        protected $old_sidebars_widgets = array();
 
+       /**
+        * Mapping of widget ID base to whether it supports selective refresh.
+        *
+        * @since 4.5.0
+        * @access protected
+        * @var array
+        */
+       protected $selective_refreshable_widgets;
+
        /**
         * Mapping of setting type to setting ID pattern.
         *
@@ -69,8 +78,8 @@ final class WP_Customize_Widgets {
         * @var array
         */
        protected $setting_id_patterns = array(
-               'widget_instance' => '/^(widget_.+?)(?:\[(\d+)\])?$/',
-               'sidebar_widgets' => '/^sidebars_widgets\[(.+?)\]$/',
+               'widget_instance' => '/^widget_(?P<id_base>.+?)(?:\[(?P<widget_number>\d+)\])?$/',
+               'sidebar_widgets' => '/^sidebars_widgets\[(?P<sidebar_id>.+?)\]$/',
        );
 
        /**
@@ -84,8 +93,13 @@ final class WP_Customize_Widgets {
        public function __construct( $manager ) {
                $this->manager = $manager;
 
+               // Skip useless hooks when the user can't manage widgets anyway.
+               if ( ! current_user_can( 'edit_theme_options' ) ) {
+                       return;
+               }
+
                add_filter( 'customize_dynamic_setting_args',          array( $this, 'filter_customize_dynamic_setting_args' ), 10, 2 );
-               add_action( 'after_setup_theme',                       array( $this, 'register_settings' ) );
+               add_action( 'widgets_init',                            array( $this, 'register_settings' ), 95 );
                add_action( 'wp_loaded',                               array( $this, 'override_sidebars_widgets_for_theme_switch' ) );
                add_action( 'customize_controls_init',                 array( $this, 'customize_controls_init' ) );
                add_action( 'customize_register',                      array( $this, 'schedule_customize_register' ), 1 );
@@ -100,16 +114,62 @@ final class WP_Customize_Widgets {
                add_action( 'dynamic_sidebar',                         array( $this, 'tally_rendered_widgets' ) );
                add_filter( 'is_active_sidebar',                       array( $this, 'tally_sidebars_via_is_active_sidebar_calls' ), 10, 2 );
                add_filter( 'dynamic_sidebar_has_widgets',             array( $this, 'tally_sidebars_via_dynamic_sidebar_calls' ), 10, 2 );
+
+               // Selective Refresh.
+               add_filter( 'customize_dynamic_partial_args',          array( $this, 'customize_dynamic_partial_args' ), 10, 2 );
+               add_action( 'customize_preview_init',                  array( $this, 'selective_refresh_init' ) );
+       }
+
+       /**
+        * List whether each registered widget can be use selective refresh.
+        *
+        * If the theme does not support the customize-selective-refresh-widgets feature,
+        * then this will always return an empty array.
+        *
+        * @since 4.5.0
+        * @access public
+        *
+        * @return array Mapping of id_base to support. If theme doesn't support
+        *               selective refresh, an empty array is returned.
+        */
+       public function get_selective_refreshable_widgets() {
+               global $wp_widget_factory;
+               if ( ! current_theme_supports( 'customize-selective-refresh-widgets' ) ) {
+                       return array();
+               }
+               if ( ! isset( $this->selective_refreshable_widgets ) ) {
+                       $this->selective_refreshable_widgets = array();
+                       foreach ( $wp_widget_factory->widgets as $wp_widget ) {
+                               $this->selective_refreshable_widgets[ $wp_widget->id_base ] = ! empty( $wp_widget->widget_options['customize_selective_refresh'] );
+                       }
+               }
+               return $this->selective_refreshable_widgets;
+       }
+
+       /**
+        * Determines if a widget supports selective refresh.
+        *
+        * @since 4.5.0
+        * @access public
+        *
+        * @param string $id_base Widget ID Base.
+        * @return bool Whether the widget can be selective refreshed.
+        */
+       public function is_widget_selective_refreshable( $id_base ) {
+               $selective_refreshable_widgets = $this->get_selective_refreshable_widgets();
+               return ! empty( $selective_refreshable_widgets[ $id_base ] );
        }
 
        /**
-        * Get the widget setting type given a setting ID.
+        * Retrieves the widget setting type given a setting ID.
         *
         * @since 4.2.0
         * @access protected
         *
-        * @param $setting_id Setting ID.
-        * @return string|null Setting type. Null otherwise.
+        * @staticvar array $cache
+        *
+        * @param string $setting_id Setting ID.
+        * @return string|void Setting type.
         */
        protected function get_setting_type( $setting_id ) {
                static $cache = array();
@@ -122,11 +182,11 @@ final class WP_Customize_Widgets {
                                return $type;
                        }
                }
-               return null;
        }
 
        /**
-        * Inspect the incoming customized data for any widget settings, and dynamically add them up-front so widgets will be initialized properly.
+        * Inspects the incoming customized data for any widget settings, and dynamically adds
+        * them up-front so widgets will be initialized properly.
         *
         * @since 4.2.0
         * @access public
@@ -158,13 +218,13 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Determine the arguments for a dynamically-created setting.
+        * Determines the arguments for a dynamically-created setting.
         *
         * @since 4.2.0
         * @access public
         *
-        * @param false|array $setting_args The arguments to the WP_Customize_Setting constructor.
-        * @param string      $setting_id   ID for dynamic setting, usually coming from `$_POST['customized']`.
+        * @param false|array $args       The arguments to the WP_Customize_Setting constructor.
+        * @param string      $setting_id ID for dynamic setting, usually coming from `$_POST['customized']`.
         * @return false|array Setting arguments, false otherwise.
         */
        public function filter_customize_dynamic_setting_args( $args, $setting_id ) {
@@ -175,10 +235,9 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Get an unslashed post value or return a default.
+        * Retrieves an unslashed post value or return a default.
         *
         * @since 3.9.0
-        *
         * @access protected
         *
         * @param string $name    Post value.
@@ -204,6 +263,9 @@ final class WP_Customize_Widgets {
         *
         * @since 3.9.0
         * @access public
+        *
+        * @global array $sidebars_widgets
+        * @global array $_wp_sidebars_widgets
         */
        public function override_sidebars_widgets_for_theme_switch() {
                global $sidebars_widgets;
@@ -219,40 +281,45 @@ final class WP_Customize_Widgets {
                $sidebars_widgets = $this->old_sidebars_widgets;
                $sidebars_widgets = retrieve_widgets( 'customize' );
                add_filter( 'option_sidebars_widgets', array( $this, 'filter_option_sidebars_widgets_for_theme_switch' ), 1 );
-               unset( $GLOBALS['_wp_sidebars_widgets'] ); // reset global cache var used by wp_get_sidebars_widgets()
+               // reset global cache var used by wp_get_sidebars_widgets()
+               unset( $GLOBALS['_wp_sidebars_widgets'] );
        }
 
        /**
-        * Filter old_sidebars_widgets_data Customizer setting.
+        * Filters old_sidebars_widgets_data Customizer setting.
         *
-        * When switching themes, filter the Customizer setting
-        * old_sidebars_widgets_data to supply initial $sidebars_widgets before they
-        * were overridden by retrieve_widgets(). The value for
-        * old_sidebars_widgets_data gets set in the old theme's sidebars_widgets
+        * When switching themes, filter the Customizer setting old_sidebars_widgets_data
+        * to supply initial $sidebars_widgets before they were overridden by retrieve_widgets().
+        * The value for old_sidebars_widgets_data gets set in the old theme's sidebars_widgets
         * theme_mod.
         *
-        * @see WP_Customize_Widgets::handle_theme_switch()
         * @since 3.9.0
         * @access public
         *
+        * @see WP_Customize_Widgets::handle_theme_switch()
+        *
         * @param array $old_sidebars_widgets
+        * @return array
         */
        public function filter_customize_value_old_sidebars_widgets_data( $old_sidebars_widgets ) {
                return $this->old_sidebars_widgets;
        }
 
        /**
-        * Filter sidebars_widgets option for theme switch.
+        * Filters sidebars_widgets option for theme switch.
         *
-        * When switching themes, the retrieve_widgets() function is run when the
-        * Customizer initializes, and then the new sidebars_widgets here get
-        * supplied as the default value for the sidebars_widgets option.
+        * When switching themes, the retrieve_widgets() function is run when the Customizer initializes,
+        * and then the new sidebars_widgets here get supplied as the default value for the sidebars_widgets
+        * option.
         *
-        * @see WP_Customize_Widgets::handle_theme_switch()
         * @since 3.9.0
         * @access public
         *
+        * @see WP_Customize_Widgets::handle_theme_switch()
+        * @global array $sidebars_widgets
+        *
         * @param array $sidebars_widgets
+        * @return array
         */
        public function filter_option_sidebars_widgets_for_theme_switch( $sidebars_widgets ) {
                $sidebars_widgets = $GLOBALS['sidebars_widgets'];
@@ -261,7 +328,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Make sure all widgets get loaded into the Customizer.
+        * Ensures all widgets get loaded into the Customizer.
         *
         * Note: these actions are also fired in wp_ajax_update_widget().
         *
@@ -280,11 +347,10 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Ensure widgets are available for all types of previews.
+        * Ensures widgets are available for all types of previews.
         *
-        * When in preview, hook to 'customize_register' for settings
-        * after WordPress is loaded so that all filters have been
-        * initialized (e.g. Widget Visibility).
+        * When in preview, hook to 'customize_register' for settings after WordPress is loaded
+        * so that all filters have been initialized (e.g. Widget Visibility).
         *
         * @since 3.9.0
         * @access public
@@ -298,17 +364,23 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Register Customizer settings and controls for all sidebars and widgets.
+        * Registers Customizer settings and controls for all sidebars and widgets.
         *
         * @since 3.9.0
         * @access public
+        *
+        * @global array $wp_registered_widgets
+        * @global array $wp_registered_widget_controls
+        * @global array $wp_registered_sidebars
         */
        public function customize_register() {
                global $wp_registered_widgets, $wp_registered_widget_controls, $wp_registered_sidebars;
 
+               add_filter( 'sidebars_widgets', array( $this, 'preview_sidebars_widgets' ), 1 );
+
                $sidebars_widgets = array_merge(
                        array( 'wp_inactive_widgets' => array() ),
-                       array_fill_keys( array_keys( $GLOBALS['wp_registered_sidebars'] ), array() ),
+                       array_fill_keys( array_keys( $wp_registered_sidebars ), array() ),
                        wp_get_sidebars_widgets()
                );
 
@@ -330,7 +402,7 @@ final class WP_Customize_Widgets {
 
                /*
                 * Add a setting which will be supplied for the theme's sidebars_widgets
-                * theme_mod when the the theme is switched.
+                * theme_mod when the theme is switched.
                 */
                if ( ! $this->manager->is_theme_active() ) {
                        $setting_id = 'old_sidebars_widgets_data';
@@ -342,9 +414,11 @@ final class WP_Customize_Widgets {
                }
 
                $this->manager->add_panel( 'widgets', array(
-                       'title'       => __( 'Widgets' ),
-                       'description' => __( 'Widgets are independent sections of content that can be placed into widgetized areas provided by your theme (commonly called sidebars).' ),
-                       'priority'    => 110,
+                       'type'            => 'widgets',
+                       'title'           => __( 'Widgets' ),
+                       'description'     => __( 'Widgets are independent sections of content that can be placed into widgetized areas provided by your theme (commonly called sidebars).' ),
+                       'priority'        => 110,
+                       'active_callback' => array( $this, 'is_panel_active' ),
                ) );
 
                foreach ( $sidebars_widgets as $sidebar_id => $sidebar_widget_ids ) {
@@ -352,7 +426,7 @@ final class WP_Customize_Widgets {
                                $sidebar_widget_ids = array();
                        }
 
-                       $is_registered_sidebar = isset( $GLOBALS['wp_registered_sidebars'][$sidebar_id] );
+                       $is_registered_sidebar = is_registered_sidebar( $sidebar_id );
                        $is_inactive_widgets   = ( 'wp_inactive_widgets' === $sidebar_id );
                        $is_active_sidebar     = ( $is_registered_sidebar && ! $is_inactive_widgets );
 
@@ -373,8 +447,8 @@ final class WP_Customize_Widgets {
                                if ( $is_active_sidebar ) {
 
                                        $section_args = array(
-                                               'title' => $GLOBALS['wp_registered_sidebars'][ $sidebar_id ]['name'],
-                                               'description' => $GLOBALS['wp_registered_sidebars'][ $sidebar_id ]['description'],
+                                               'title' => $wp_registered_sidebars[ $sidebar_id ]['name'],
+                                               'description' => $wp_registered_sidebars[ $sidebar_id ]['description'],
                                                'priority' => array_search( $sidebar_id, array_keys( $wp_registered_sidebars ) ),
                                                'panel' => 'widgets',
                                                'sidebar_id' => $sidebar_id,
@@ -409,13 +483,13 @@ final class WP_Customize_Widgets {
                        foreach ( $sidebar_widget_ids as $i => $widget_id ) {
 
                                // Skip widgets that may have gone away due to a plugin being deactivated.
-                               if ( ! $is_active_sidebar || ! isset( $GLOBALS['wp_registered_widgets'][$widget_id] ) ) {
+                               if ( ! $is_active_sidebar || ! isset( $wp_registered_widgets[$widget_id] ) ) {
                                        continue;
                                }
 
-                               $registered_widget = $GLOBALS['wp_registered_widgets'][$widget_id];
+                               $registered_widget = $wp_registered_widgets[$widget_id];
                                $setting_id        = $this->get_setting_id( $widget_id );
-                               $id_base           = $GLOBALS['wp_registered_widget_controls'][$widget_id]['id_base'];
+                               $id_base           = $wp_registered_widget_controls[$widget_id]['id_base'];
 
                                $control = new WP_Widget_Form_Customize_Control( $this->manager, $setting_id, array(
                                        'label'          => $registered_widget['name'],
@@ -437,12 +511,26 @@ final class WP_Customize_Widgets {
                                $this->manager->get_setting( $new_setting_id )->preview();
                        }
                }
+       }
 
-               add_filter( 'sidebars_widgets', array( $this, 'preview_sidebars_widgets' ), 1 );
+       /**
+        * Determines whether the widgets panel is active, based on whether there are sidebars registered.
+        *
+        * @since 4.4.0
+        * @access public
+        *
+        * @see WP_Customize_Panel::$active_callback
+        *
+        * @global array $wp_registered_sidebars
+        * @return bool Active.
+        */
+       public function is_panel_active() {
+               global $wp_registered_sidebars;
+               return ! empty( $wp_registered_sidebars );
        }
 
        /**
-        * Covert a widget_id into its corresponding Customizer setting ID (option name).
+        * Converts a widget_id into its corresponding Customizer setting ID (option name).
         *
         * @since 3.9.0
         * @access public
@@ -461,18 +549,20 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Determine whether the widget is considered "wide".
+        * Determines whether the widget is considered "wide".
         *
-        * Core widgets which may have controls wider than 250, but can
-        * still be shown in the narrow Customizer panel. The RSS and Text
-        * widgets in Core, for example, have widths of 400 and yet they
-        * still render fine in the Customizer panel. This method will
-        * return all Core widgets as being not wide, but this can be
+        * Core widgets which may have controls wider than 250, but can still be shown
+        * in the narrow Customizer panel. The RSS and Text widgets in Core, for example,
+        * have widths of 400 and yet they still render fine in the Customizer panel.
+        *
+        * This method will return all Core widgets as being not wide, but this can be
         * overridden with the is_wide_widget_in_customizer filter.
         *
         * @since 3.9.0
         * @access public
         *
+        * @global $wp_registered_widget_controls
+        *
         * @param string $widget_id Widget ID.
         * @return bool Whether or not the widget is a "wide" widget.
         */
@@ -496,7 +586,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Covert a widget ID into its id_base and number components.
+        * Converts a widget ID into its id_base and number components.
         *
         * @since 3.9.0
         * @access public
@@ -521,7 +611,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Convert a widget setting ID (option path) to its id_base and number components.
+        * Converts a widget setting ID (option path) to its id_base and number components.
         *
         * @since 3.9.0
         * @access public
@@ -542,7 +632,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Call admin_print_styles-widgets.php and admin_print_styles hooks to
+        * Calls admin_print_styles-widgets.php and admin_print_styles hooks to
         * allow custom styles from plugins.
         *
         * @since 3.9.0
@@ -557,7 +647,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Call admin_print_scripts-widgets.php and admin_print_scripts hooks to
+        * Calls admin_print_scripts-widgets.php and admin_print_scripts hooks to
         * allow custom scripts from plugins.
         *
         * @since 3.9.0
@@ -572,12 +662,18 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Enqueue scripts and styles for Customizer panel and export data to JavaScript.
+        * Enqueues scripts and styles for Customizer panel and export data to JavaScript.
         *
         * @since 3.9.0
         * @access public
+        *
+        * @global WP_Scripts $wp_scripts
+        * @global array $wp_registered_sidebars
+        * @global array $wp_registered_widgets
         */
        public function enqueue_scripts() {
+               global $wp_scripts, $wp_registered_sidebars, $wp_registered_widgets;
+
                wp_enqueue_style( 'customize-widgets' );
                wp_enqueue_script( 'customize-widgets' );
 
@@ -621,12 +717,9 @@ final class WP_Customize_Widgets {
                        </div>'
                );
 
-               global $wp_scripts;
-
                $settings = array(
-                       'nonce'                => wp_create_nonce( 'update-widget' ),
-                       'registeredSidebars'   => array_values( $GLOBALS['wp_registered_sidebars'] ),
-                       'registeredWidgets'    => $GLOBALS['wp_registered_widgets'],
+                       'registeredSidebars'   => array_values( $wp_registered_sidebars ),
+                       'registeredWidgets'    => $wp_registered_widgets,
                        'availableWidgets'     => $available_widgets, // @todo Merge this with registered_widgets
                        'l10n' => array(
                                'saveBtnLabel'     => __( 'Apply' ),
@@ -636,11 +729,17 @@ final class WP_Customize_Widgets {
                                'error'            => __( 'An error has occurred. Please reload the page and try again.' ),
                                'widgetMovedUp'    => __( 'Widget moved up' ),
                                'widgetMovedDown'  => __( 'Widget moved down' ),
+                               'noAreasRendered'  => __( 'There are no widget areas currently rendered in the preview. Navigate in the preview to a template that makes use of a widget area in order to access its widgets here.' ),
+                               'reorderModeOn'    => __( 'Reorder mode enabled' ),
+                               'reorderModeOff'   => __( 'Reorder mode closed' ),
+                               'reorderLabelOn'   => esc_attr__( 'Reorder widgets' ),
+                               'reorderLabelOff'  => esc_attr__( 'Close reorder mode' ),
                        ),
                        'tpl' => array(
                                'widgetReorderNav' => $widget_reorder_nav_tpl,
                                'moveWidgetArea'   => $move_widget_area_tpl,
                        ),
+                       'selectiveRefreshableWidgets' => $this->get_selective_refreshable_widgets(),
                );
 
                foreach ( $settings['registeredWidgets'] as &$registered_widget ) {
@@ -655,7 +754,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Render the widget form control templates into the DOM.
+        * Renders the widget form control templates into the DOM.
         *
         * @since 3.9.0
         * @access public
@@ -664,6 +763,18 @@ final class WP_Customize_Widgets {
                ?>
                <div id="widgets-left"><!-- compatibility with JS which looks for widget templates here -->
                <div id="available-widgets">
+                       <div class="customize-section-title">
+                               <button class="customize-section-back" tabindex="-1">
+                                       <span class="screen-reader-text"><?php _e( 'Back' ); ?></span>
+                               </button>
+                               <h3>
+                                       <span class="customize-action"><?php
+                                               /* translators: &#9656; is the unicode right-pointing triangle, and %s is the section title in the Customizer */
+                                               echo sprintf( __( 'Customizing &#9656; %s' ), esc_html( $this->manager->get_panel( 'widgets' )->title ) );
+                                       ?></span>
+                                       <?php _e( 'Add a Widget' ); ?>
+                               </h3>
+                       </div>
                        <div id="available-widgets-filter">
                                <label class="screen-reader-text" for="widgets-search"><?php _e( 'Search Widgets' ); ?></label>
                                <input type="search" id="widgets-search" placeholder="<?php esc_attr_e( 'Search widgets&hellip;' ) ?>" />
@@ -681,7 +792,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Call admin_print_footer_scripts and admin_print_scripts hooks to
+        * Calls admin_print_footer_scripts and admin_print_scripts hooks to
         * allow custom scripts from plugins.
         *
         * @since 3.9.0
@@ -696,7 +807,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Get common arguments to supply when constructing a Customizer setting.
+        * Retrieves common arguments to supply when constructing a Customizer setting.
         *
         * @since 3.9.0
         * @access public
@@ -709,16 +820,17 @@ final class WP_Customize_Widgets {
                $args = array(
                        'type'       => 'option',
                        'capability' => 'edit_theme_options',
-                       'transport'  => 'refresh',
                        'default'    => array(),
                );
 
                if ( preg_match( $this->setting_id_patterns['sidebar_widgets'], $id, $matches ) ) {
                        $args['sanitize_callback'] = array( $this, 'sanitize_sidebar_widgets' );
                        $args['sanitize_js_callback'] = array( $this, 'sanitize_sidebar_widgets_js_instance' );
-               } else if ( preg_match( $this->setting_id_patterns['widget_instance'], $id, $matches ) ) {
+                       $args['transport'] = current_theme_supports( 'customize-selective-refresh-widgets' ) ? 'postMessage' : 'refresh';
+               } elseif ( preg_match( $this->setting_id_patterns['widget_instance'], $id, $matches ) ) {
                        $args['sanitize_callback'] = array( $this, 'sanitize_widget_instance' );
                        $args['sanitize_js_callback'] = array( $this, 'sanitize_widget_js_instance' );
+                       $args['transport'] = $this->is_widget_selective_refreshable( $matches['id_base'] ) ? 'postMessage' : 'refresh';
                }
 
                $args = array_merge( $args, $overrides );
@@ -737,7 +849,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Make sure that sidebar widget arrays only ever contain widget IDS.
+        * Ensures sidebar widget arrays only ever contain widget IDS.
         *
         * Used as the 'sanitize_callback' for each $sidebars_widgets setting.
         *
@@ -757,11 +869,15 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Build up an index of all available widgets for use in Backbone models.
+        * Builds up an index of all available widgets for use in Backbone models.
         *
         * @since 3.9.0
         * @access public
         *
+        * @global array $wp_registered_widgets
+        * @global array $wp_registered_widget_controls
+        * @staticvar array $available_widgets
+        *
         * @see wp_list_widgets()
         *
         * @return array List of available widgets.
@@ -827,7 +943,7 @@ final class WP_Customize_Widgets {
                                'multi_number' => ( $args['_add'] === 'multi' ) ? $args['_multi_num'] : false,
                                'is_disabled'  => $is_disabled,
                                'id_base'      => $id_base,
-                               'transport'    => 'refresh',
+                               'transport'    => $this->is_widget_selective_refreshable( $id_base ) ? 'postMessage' : 'refresh',
                                'width'        => $wp_registered_widget_controls[$widget['id']]['width'],
                                'height'       => $wp_registered_widget_controls[$widget['id']]['height'],
                                'is_wide'      => $this->is_wide_widget( $widget['id'] ),
@@ -840,10 +956,9 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Naturally order available widgets by name.
+        * Naturally orders available widgets by name.
         *
         * @since 3.9.0
-        * @static
         * @access protected
         *
         * @param array $widget_a The first widget to compare.
@@ -855,7 +970,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Get the widget control markup.
+        * Retrieves the widget control markup.
         *
         * @since 3.9.0
         * @access public
@@ -864,23 +979,49 @@ final class WP_Customize_Widgets {
         * @return string Widget control form HTML markup.
         */
        public function get_widget_control( $args ) {
+               $args[0]['before_form'] = '<div class="form">';
+               $args[0]['after_form'] = '</div><!-- .form -->';
+               $args[0]['before_widget_content'] = '<div class="widget-content">';
+               $args[0]['after_widget_content'] = '</div><!-- .widget-content -->';
                ob_start();
-
                call_user_func_array( 'wp_widget_control', $args );
-               $replacements = array(
-                       '<form method="post">' => '<div class="form">',
-                       '</form>' => '</div><!-- .form -->',
-               );
-
                $control_tpl = ob_get_clean();
+               return $control_tpl;
+       }
 
-               $control_tpl = str_replace( array_keys( $replacements ), array_values( $replacements ), $control_tpl );
+       /**
+        * Retrieves the widget control markup parts.
+        *
+        * @since 4.4.0
+        * @access public
+        *
+        * @param array $args Widget control arguments.
+        * @return array {
+        *     @type string $control Markup for widget control wrapping form.
+        *     @type string $content The contents of the widget form itself.
+        * }
+        */
+       public function get_widget_control_parts( $args ) {
+               $args[0]['before_widget_content'] = '<div class="widget-content">';
+               $args[0]['after_widget_content'] = '</div><!-- .widget-content -->';
+               $control_markup = $this->get_widget_control( $args );
+
+               $content_start_pos = strpos( $control_markup, $args[0]['before_widget_content'] );
+               $content_end_pos = strrpos( $control_markup, $args[0]['after_widget_content'] );
+
+               $control = substr( $control_markup, 0, $content_start_pos + strlen( $args[0]['before_widget_content'] ) );
+               $control .= substr( $control_markup, $content_end_pos );
+               $content = trim( substr(
+                       $control_markup,
+                       $content_start_pos + strlen( $args[0]['before_widget_content'] ),
+                       $content_end_pos - $content_start_pos - strlen( $args[0]['before_widget_content'] )
+               ) );
 
-               return $control_tpl;
+               return compact( 'control', 'content' );
        }
 
        /**
-        * Add hooks for the Customizer preview.
+        * Adds hooks for the Customizer preview.
         *
         * @since 3.9.0
         * @access public
@@ -892,7 +1033,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Refresh nonce for widget updates.
+        * Refreshes the nonce for widget updates.
         *
         * @since 4.2.0
         * @access public
@@ -906,18 +1047,18 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * When previewing, make sure the proper previewing widgets are used.
+        * When previewing, ensures the proper previewing widgets are used.
         *
-        * Because wp_get_sidebars_widgets() gets called early at init
-        * (via wp_convert_widget_settings()) and can set global variable
-        * $_wp_sidebars_widgets to the value of get_option( 'sidebars_widgets' )
-        * before the Customizer preview filter is added, we have to reset
-        * it after the filter has been added.
+        * Because wp_get_sidebars_widgets() gets called early at {@see 'init' } (via
+        * wp_convert_widget_settings()) and can set global variable `$_wp_sidebars_widgets`
+        * to the value of `get_option( 'sidebars_widgets' )` before the Customizer preview
+        * filter is added, it has to be reset after the filter has been added.
         *
         * @since 3.9.0
         * @access public
         *
         * @param array $sidebars_widgets List of widgets for the current sidebar.
+        * @return array
         */
        public function preview_sidebars_widgets( $sidebars_widgets ) {
                $sidebars_widgets = get_option( 'sidebars_widgets' );
@@ -927,23 +1068,22 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Enqueue scripts for the Customizer preview.
+        * Enqueues scripts for the Customizer preview.
         *
         * @since 3.9.0
         * @access public
         */
        public function customize_preview_enqueue() {
                wp_enqueue_script( 'customize-preview-widgets' );
+               wp_enqueue_style( 'customize-preview' );
        }
 
        /**
-        * Insert default style for highlighted widget at early point so theme
+        * Inserts default style for highlighted widget at early point so theme
         * stylesheet can override.
         *
         * @since 3.9.0
         * @access public
-        *
-        * @action wp_print_styles
         */
        public function print_preview_css() {
                ?>
@@ -960,23 +1100,28 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * At the very end of the page, at the very end of the wp_footer,
-        * communicate the sidebars that appeared on the page.
+        * Communicates the sidebars that appeared on the page at the very end of the page,
+        * and at the very end of the wp_footer,
         *
         * @since 3.9.0
         * @access public
+     *
+        * @global array $wp_registered_sidebars
+        * @global array $wp_registered_widgets
         */
        public function export_preview_data() {
+               global $wp_registered_sidebars, $wp_registered_widgets;
 
                // Prepare Customizer settings to pass to JavaScript.
                $settings = array(
                        'renderedSidebars'   => array_fill_keys( array_unique( $this->rendered_sidebars ), true ),
                        'renderedWidgets'    => array_fill_keys( array_keys( $this->rendered_widgets ), true ),
-                       'registeredSidebars' => array_values( $GLOBALS['wp_registered_sidebars'] ),
-                       'registeredWidgets'  => $GLOBALS['wp_registered_widgets'],
+                       'registeredSidebars' => array_values( $wp_registered_sidebars ),
+                       'registeredWidgets'  => $wp_registered_widgets,
                        'l10n'               => array(
-                               'widgetTooltip' => __( 'Shift-click to edit this widget.' ),
+                               'widgetTooltip'  => __( 'Shift-click to edit this widget.' ),
                        ),
+                       'selectiveRefreshableWidgets' => $this->get_selective_refreshable_widgets(),
                );
                foreach ( $settings['registeredWidgets'] as &$registered_widget ) {
                        unset( $registered_widget['callback'] ); // may not be JSON-serializeable
@@ -990,7 +1135,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Keep track of the widgets that were rendered.
+        * Tracks the widgets that were rendered.
         *
         * @since 3.9.0
         * @access public
@@ -1015,7 +1160,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Determine if a sidebar is rendered on the page.
+        * Determines if a sidebar is rendered on the page.
         *
         * @since 4.0.0
         * @access public
@@ -1028,21 +1173,21 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Tally the sidebars rendered via is_active_sidebar().
+        * Tallies the sidebars rendered via is_active_sidebar().
         *
-        * Keep track of the times that is_active_sidebar() is called
-        * in the template, and assume that this means that the sidebar
-        * would be rendered on the template if there were widgets
-        * populating it.
+        * Keep track of the times that is_active_sidebar() is called in the template,
+        * and assume that this means that the sidebar would be rendered on the template
+        * if there were widgets populating it.
         *
         * @since 3.9.0
         * @access public
         *
         * @param bool   $is_active  Whether the sidebar is active.
         * @param string $sidebar_id Sidebar ID.
+        * @return bool Whether the sidebar is active.
         */
        public function tally_sidebars_via_is_active_sidebar_calls( $is_active, $sidebar_id ) {
-               if ( isset( $GLOBALS['wp_registered_sidebars'][$sidebar_id] ) ) {
+               if ( is_registered_sidebar( $sidebar_id ) ) {
                        $this->rendered_sidebars[] = $sidebar_id;
                }
                /*
@@ -1054,7 +1199,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Tally the sidebars rendered via dynamic_sidebar().
+        * Tallies the sidebars rendered via dynamic_sidebar().
         *
         * Keep track of the times that dynamic_sidebar() is called in the template,
         * and assume this means the sidebar would be rendered on the template if
@@ -1065,9 +1210,10 @@ final class WP_Customize_Widgets {
         *
         * @param bool   $has_widgets Whether the current sidebar has widgets.
         * @param string $sidebar_id  Sidebar ID.
+        * @return bool Whether the current sidebar has widgets.
         */
        public function tally_sidebars_via_dynamic_sidebar_calls( $has_widgets, $sidebar_id ) {
-               if ( isset( $GLOBALS['wp_registered_sidebars'][$sidebar_id] ) ) {
+               if ( is_registered_sidebar( $sidebar_id ) ) {
                        $this->rendered_sidebars[] = $sidebar_id;
                }
 
@@ -1080,7 +1226,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Get MAC for a serialized widget instance string.
+        * Retrieves MAC for a serialized widget instance string.
         *
         * Allows values posted back from JS to be rejected if any tampering of the
         * data has occurred.
@@ -1096,16 +1242,16 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Sanitize a widget instance.
+        * Sanitizes a widget instance.
         *
-        * Unserialize the JS-instance for storing in the options. It's important
-        * that this filter only get applied to an instance once.
+        * Unserialize the JS-instance for storing in the options. It's important that this filter
+        * only get applied to an instance *once*.
         *
         * @since 3.9.0
         * @access public
         *
         * @param array $value Widget instance to sanitize.
-        * @return array Sanitized widget instance.
+        * @return array|void Sanitized widget instance.
         */
        public function sanitize_widget_instance( $value ) {
                if ( $value === array() ) {
@@ -1116,28 +1262,28 @@ final class WP_Customize_Widgets {
                        || empty( $value['instance_hash_key'] )
                        || empty( $value['encoded_serialized_instance'] ) )
                {
-                       return null;
+                       return;
                }
 
                $decoded = base64_decode( $value['encoded_serialized_instance'], true );
                if ( false === $decoded ) {
-                       return null;
+                       return;
                }
 
                if ( ! hash_equals( $this->get_instance_hash_key( $decoded ), $value['instance_hash_key'] ) ) {
-                       return null;
+                       return;
                }
 
                $instance = unserialize( $decoded );
                if ( false === $instance ) {
-                       return null;
+                       return;
                }
 
                return $instance;
        }
 
        /**
-        * Convert widget instance into JSON-representable format.
+        * Converts a widget instance into JSON-representable format.
         *
         * @since 3.9.0
         * @access public
@@ -1160,7 +1306,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Strip out widget IDs for widgets which are no longer registered.
+        * Strips out widget IDs for widgets which are no longer registered.
         *
         * One example where this might happen is when a plugin orphans a widget
         * in a sidebar upon deactivation.
@@ -1168,6 +1314,8 @@ final class WP_Customize_Widgets {
         * @since 3.9.0
         * @access public
         *
+        * @global array $wp_registered_widgets
+        *
         * @param array $widget_ids List of widget IDs.
         * @return array Parsed list of widget IDs.
         */
@@ -1178,13 +1326,16 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Find and invoke the widget update and control callbacks.
+        * Finds and invokes the widget update and control callbacks.
         *
-        * Requires that $_POST be populated with the instance data.
+        * Requires that `$_POST` be populated with the instance data.
         *
         * @since 3.9.0
         * @access public
         *
+        * @global array $wp_registered_widget_updates
+        * @global array $wp_registered_widget_controls
+        *
         * @param  string $widget_id Widget ID.
         * @return WP_Error|array Array containing the updated widget information.
         *                        A WP_Error object, otherwise.
@@ -1192,6 +1343,20 @@ final class WP_Customize_Widgets {
        public function call_widget_update( $widget_id ) {
                global $wp_registered_widget_updates, $wp_registered_widget_controls;
 
+               $setting_id = $this->get_setting_id( $widget_id );
+
+               /*
+                * Make sure that other setting changes have previewed since this widget
+                * may depend on them (e.g. Menus being present for Custom Menu widget).
+                */
+               if ( ! did_action( 'customize_preview_init' ) ) {
+                       foreach ( $this->manager->settings() as $setting ) {
+                               if ( $setting->id !== $setting_id ) {
+                                       $setting->preview();
+                               }
+                       }
+               }
+
                $this->start_capturing_option_updates();
                $parsed_id   = $this->parse_widget_id( $widget_id );
                $option_name = 'widget_' . $parsed_id['id_base'];
@@ -1272,8 +1437,7 @@ final class WP_Customize_Widgets {
                 * in place from WP_Customize_Setting::preview() will use this value
                 * instead of the default widget instance value (an empty array).
                 */
-               $setting_id = $this->get_setting_id( $widget_id );
-               $this->manager->set_post_value( $setting_id, $instance );
+               $this->manager->set_post_value( $setting_id, $this->sanitize_widget_js_instance( $instance ) );
 
                // Obtain the widget control with the updated instance in place.
                ob_start();
@@ -1289,18 +1453,17 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Update widget settings asynchronously.
+        * Updates widget settings asynchronously.
         *
         * Allows the Customizer to update a widget using its form, but return the new
         * instance info via Ajax instead of saving it to the options table.
         *
-        * Most code here copied from wp_ajax_save_widget()
+        * Most code here copied from wp_ajax_save_widget().
         *
         * @since 3.9.0
         * @access public
         *
         * @see wp_ajax_save_widget()
-        *
         */
        public function wp_ajax_update_widget() {
 
@@ -1344,7 +1507,7 @@ final class WP_Customize_Widgets {
 
                $updated_widget = $this->call_widget_update( $widget_id ); // => {instance,form}
                if ( is_wp_error( $updated_widget ) ) {
-                       wp_send_json_error( $updated_widget->get_error_message() );
+                       wp_send_json_error( $updated_widget->get_error_code() );
                }
 
                $form = $updated_widget['form'];
@@ -1353,9 +1516,316 @@ final class WP_Customize_Widgets {
                wp_send_json_success( compact( 'form', 'instance' ) );
        }
 
-       /***************************************************************************
-        * Option Update Capturing
-        ***************************************************************************/
+       /*
+        * Selective Refresh Methods
+        */
+
+       /**
+        * Filters arguments for dynamic widget partials.
+        *
+        * @since 4.5.0
+        * @access public
+        *
+        * @param array|false $partial_args Partial arguments.
+        * @param string      $partial_id   Partial ID.
+        * @return array (Maybe) modified partial arguments.
+        */
+       public function customize_dynamic_partial_args( $partial_args, $partial_id ) {
+               if ( ! current_theme_supports( 'customize-selective-refresh-widgets' ) ) {
+                       return $partial_args;
+               }
+
+               if ( preg_match( '/^widget\[(?P<widget_id>.+)\]$/', $partial_id, $matches ) ) {
+                       if ( false === $partial_args ) {
+                               $partial_args = array();
+                       }
+                       $partial_args = array_merge(
+                               $partial_args,
+                               array(
+                                       'type'                => 'widget',
+                                       'render_callback'     => array( $this, 'render_widget_partial' ),
+                                       'container_inclusive' => true,
+                                       'settings'            => array( $this->get_setting_id( $matches['widget_id'] ) ),
+                                       'capability'          => 'edit_theme_options',
+                               )
+                       );
+               }
+
+               return $partial_args;
+       }
+
+       /**
+        * Adds hooks for selective refresh.
+        *
+        * @since 4.5.0
+        * @access public
+        */
+       public function selective_refresh_init() {
+               if ( ! current_theme_supports( 'customize-selective-refresh-widgets' ) ) {
+                       return;
+               }
+               add_filter( 'dynamic_sidebar_params', array( $this, 'filter_dynamic_sidebar_params' ) );
+               add_filter( 'wp_kses_allowed_html', array( $this, 'filter_wp_kses_allowed_data_attributes' ) );
+               add_action( 'dynamic_sidebar_before', array( $this, 'start_dynamic_sidebar' ) );
+               add_action( 'dynamic_sidebar_after', array( $this, 'end_dynamic_sidebar' ) );
+       }
+
+       /**
+        * Inject selective refresh data attributes into widget container elements.
+        *
+        * @param array $params {
+        *     Dynamic sidebar params.
+        *
+        *     @type array $args        Sidebar args.
+        *     @type array $widget_args Widget args.
+        * }
+        * @see WP_Customize_Nav_Menus_Partial_Refresh::filter_wp_nav_menu_args()
+        *
+        * @return array Params.
+        */
+       public function filter_dynamic_sidebar_params( $params ) {
+               $sidebar_args = array_merge(
+                       array(
+                               'before_widget' => '',
+                               'after_widget' => '',
+                       ),
+                       $params[0]
+               );
+
+               // Skip widgets not in a registered sidebar or ones which lack a proper wrapper element to attach the data-* attributes to.
+               $matches = array();
+               $is_valid = (
+                       isset( $sidebar_args['id'] )
+                       &&
+                       is_registered_sidebar( $sidebar_args['id'] )
+                       &&
+                       ( isset( $this->current_dynamic_sidebar_id_stack[0] ) && $this->current_dynamic_sidebar_id_stack[0] === $sidebar_args['id'] )
+                       &&
+                       preg_match( '#^<(?P<tag_name>\w+)#', $sidebar_args['before_widget'], $matches )
+               );
+               if ( ! $is_valid ) {
+                       return $params;
+               }
+               $this->before_widget_tags_seen[ $matches['tag_name'] ] = true;
+
+               $context = array(
+                       'sidebar_id' => $sidebar_args['id'],
+               );
+               if ( isset( $this->context_sidebar_instance_number ) ) {
+                       $context['sidebar_instance_number'] = $this->context_sidebar_instance_number;
+               } else if ( isset( $sidebar_args['id'] ) && isset( $this->sidebar_instance_count[ $sidebar_args['id'] ] ) ) {
+                       $context['sidebar_instance_number'] = $this->sidebar_instance_count[ $sidebar_args['id'] ];
+               }
+
+               $attributes = sprintf( ' data-customize-partial-id="%s"', esc_attr( 'widget[' . $sidebar_args['widget_id'] . ']' ) );
+               $attributes .= ' data-customize-partial-type="widget"';
+               $attributes .= sprintf( ' data-customize-partial-placement-context="%s"', esc_attr( wp_json_encode( $context ) ) );
+               $attributes .= sprintf( ' data-customize-widget-id="%s"', esc_attr( $sidebar_args['widget_id'] ) );
+               $sidebar_args['before_widget'] = preg_replace( '#^(<\w+)#', '$1 ' . $attributes, $sidebar_args['before_widget'] );
+
+               $params[0] = $sidebar_args;
+               return $params;
+       }
+
+       /**
+        * List of the tag names seen for before_widget strings.
+        *
+        * This is used in the {@see 'filter_wp_kses_allowed_html'} filter to ensure that the
+        * data-* attributes can be whitelisted.
+        *
+        * @since 4.5.0
+        * @access protected
+        * @var array
+        */
+       protected $before_widget_tags_seen = array();
+
+       /**
+        * Ensures the HTML data-* attributes for selective refresh are allowed by kses.
+        *
+        * This is needed in case the `$before_widget` is run through wp_kses() when printed.
+        *
+        * @since 4.5.0
+        * @access public
+        *
+        * @param array $allowed_html Allowed HTML.
+        * @return array (Maybe) modified allowed HTML.
+        */
+       public function filter_wp_kses_allowed_data_attributes( $allowed_html ) {
+               foreach ( array_keys( $this->before_widget_tags_seen ) as $tag_name ) {
+                       if ( ! isset( $allowed_html[ $tag_name ] ) ) {
+                               $allowed_html[ $tag_name ] = array();
+                       }
+                       $allowed_html[ $tag_name ] = array_merge(
+                               $allowed_html[ $tag_name ],
+                               array_fill_keys( array(
+                                       'data-customize-partial-id',
+                                       'data-customize-partial-type',
+                                       'data-customize-partial-placement-context',
+                                       'data-customize-partial-widget-id',
+                                       'data-customize-partial-options',
+                               ), true )
+                       );
+               }
+               return $allowed_html;
+       }
+
+       /**
+        * Keep track of the number of times that dynamic_sidebar() was called for a given sidebar index.
+        *
+        * This helps facilitate the uncommon scenario where a single sidebar is rendered multiple times on a template.
+        *
+        * @since 4.5.0
+        * @access protected
+        * @var array
+        */
+       protected $sidebar_instance_count = array();
+
+       /**
+        * The current request's sidebar_instance_number context.
+        *
+        * @since 4.5.0
+        * @access protected
+        * @var int
+        */
+       protected $context_sidebar_instance_number;
+
+       /**
+        * Current sidebar ID being rendered.
+        *
+        * @since 4.5.0
+        * @access protected
+        * @var array
+        */
+       protected $current_dynamic_sidebar_id_stack = array();
+
+       /**
+        * Begins keeping track of the current sidebar being rendered.
+        *
+        * Insert marker before widgets are rendered in a dynamic sidebar.
+        *
+        * @since 4.5.0
+        * @access public
+        *
+        * @param int|string $index Index, name, or ID of the dynamic sidebar.
+        */
+       public function start_dynamic_sidebar( $index ) {
+               array_unshift( $this->current_dynamic_sidebar_id_stack, $index );
+               if ( ! isset( $this->sidebar_instance_count[ $index ] ) ) {
+                       $this->sidebar_instance_count[ $index ] = 0;
+               }
+               $this->sidebar_instance_count[ $index ] += 1;
+               if ( ! $this->manager->selective_refresh->is_render_partials_request() ) {
+                       printf( "\n<!--dynamic_sidebar_before:%s:%d-->\n", esc_html( $index ), intval( $this->sidebar_instance_count[ $index ] ) );
+               }
+       }
+
+       /**
+        * Finishes keeping track of the current sidebar being rendered.
+        *
+        * Inserts a marker after widgets are rendered in a dynamic sidebar.
+        *
+        * @since 4.5.0
+        * @access public
+        *
+        * @param int|string $index Index, name, or ID of the dynamic sidebar.
+        */
+       public function end_dynamic_sidebar( $index ) {
+               array_shift( $this->current_dynamic_sidebar_id_stack );
+               if ( ! $this->manager->selective_refresh->is_render_partials_request() ) {
+                       printf( "\n<!--dynamic_sidebar_after:%s:%d-->\n", esc_html( $index ), intval( $this->sidebar_instance_count[ $index ] ) );
+               }
+       }
+
+       /**
+        * Current sidebar being rendered.
+        *
+        * @since 4.5.0
+        * @access protected
+        * @var string
+        */
+       protected $rendering_widget_id;
+
+       /**
+        * Current widget being rendered.
+        *
+        * @since 4.5.0
+        * @access protected
+        * @var string
+        */
+       protected $rendering_sidebar_id;
+
+       /**
+        * Filters sidebars_widgets to ensure the currently-rendered widget is the only widget in the current sidebar.
+        *
+        * @since 4.5.0
+        * @access protected
+        *
+        * @param array $sidebars_widgets Sidebars widgets.
+        * @return array Filtered sidebars widgets.
+        */
+       public function filter_sidebars_widgets_for_rendering_widget( $sidebars_widgets ) {
+               $sidebars_widgets[ $this->rendering_sidebar_id ] = array( $this->rendering_widget_id );
+               return $sidebars_widgets;
+       }
+
+       /**
+        * Renders a specific widget using the supplied sidebar arguments.
+        *
+        * @since 4.5.0
+        * @access public
+        *
+        * @see dynamic_sidebar()
+        *
+        * @param WP_Customize_Partial $partial Partial.
+        * @param array                $context {
+        *     Sidebar args supplied as container context.
+        *
+        *     @type string $sidebar_id              ID for sidebar for widget to render into.
+        *     @type int    $sidebar_instance_number Disambiguating instance number.
+        * }
+        * @return string|false
+        */
+       public function render_widget_partial( $partial, $context ) {
+               $id_data   = $partial->id_data();
+               $widget_id = array_shift( $id_data['keys'] );
+
+               if ( ! is_array( $context )
+                       || empty( $context['sidebar_id'] )
+                       || ! is_registered_sidebar( $context['sidebar_id'] )
+               ) {
+                       return false;
+               }
+
+               $this->rendering_sidebar_id = $context['sidebar_id'];
+
+               if ( isset( $context['sidebar_instance_number'] ) ) {
+                       $this->context_sidebar_instance_number = intval( $context['sidebar_instance_number'] );
+               }
+
+               // Filter sidebars_widgets so that only the queried widget is in the sidebar.
+               $this->rendering_widget_id = $widget_id;
+
+               $filter_callback = array( $this, 'filter_sidebars_widgets_for_rendering_widget' );
+               add_filter( 'sidebars_widgets', $filter_callback, 1000 );
+
+               // Render the widget.
+               ob_start();
+               dynamic_sidebar( $this->rendering_sidebar_id = $context['sidebar_id'] );
+               $container = ob_get_clean();
+
+               // Reset variables for next partial render.
+               remove_filter( 'sidebars_widgets', $filter_callback, 1000 );
+
+               $this->context_sidebar_instance_number = null;
+               $this->rendering_sidebar_id = null;
+               $this->rendering_widget_id = null;
+
+               return $container;
+       }
+
+       //
+       // Option Update Capturing
+       //
 
        /**
         * List of captured widget option updates.
@@ -1376,20 +1846,20 @@ final class WP_Customize_Widgets {
        protected $_is_capturing_option_updates = false;
 
        /**
-        * Determine whether the captured option update should be ignored.
+        * Determines whether the captured option update should be ignored.
         *
         * @since 3.9.0
         * @access protected
         *
         * @param string $option_name Option name.
-        * @return boolean Whether the option capture is ignored.
+        * @return bool Whether the option capture is ignored.
         */
        protected function is_option_capture_ignored( $option_name ) {
                return ( 0 === strpos( $option_name, '_transient_' ) );
        }
 
        /**
-        * Retrieve captured widget option updates.
+        * Retrieves captured widget option updates.
         *
         * @since 3.9.0
         * @access protected
@@ -1401,13 +1871,13 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Get the option that was captured from being saved.
+        * Retrieves the option that was captured from being saved.
         *
         * @since 4.2.0
         * @access protected
         *
         * @param string $option_name Option name.
-        * @param mixed  $default     Optional. Default value to return if the option does not exist.
+        * @param mixed  $default     Optional. Default value to return if the option does not exist. Default false.
         * @return mixed Value set for the option.
         */
        protected function get_captured_option( $option_name, $default = false ) {
@@ -1420,7 +1890,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Get the number of captured widget option updates.
+        * Retrieves the number of captured widget option updates.
         *
         * @since 3.9.0
         * @access protected
@@ -1432,7 +1902,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Start keeping track of changes to widget options, caching new values.
+        * Begins keeping track of changes to widget options, caching new values.
         *
         * @since 3.9.0
         * @access protected
@@ -1448,7 +1918,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Pre-filter captured option values before updating.
+        * Pre-filters captured option values before updating.
         *
         * @since 3.9.0
         * @access public
@@ -1473,7 +1943,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Pre-filter captured option values before retrieving.
+        * Pre-filters captured option values before retrieving.
         *
         * @since 3.9.0
         * @access public
@@ -1495,7 +1965,7 @@ final class WP_Customize_Widgets {
        }
 
        /**
-        * Undo any changes to the options since options capture began.
+        * Undoes any changes to the options since options capture began.
         *
         * @since 3.9.0
         * @access protected
@@ -1505,7 +1975,7 @@ final class WP_Customize_Widgets {
                        return;
                }
 
-               remove_filter( 'pre_update_option', array( $this, 'capture_filter_pre_update_option' ), 10, 3 );
+               remove_filter( 'pre_update_option', array( $this, 'capture_filter_pre_update_option' ), 10 );
 
                foreach ( array_keys( $this->_captured_options ) as $option_name ) {
                        remove_filter( "pre_option_{$option_name}", array( $this, 'capture_filter_pre_get_option' ) );