Adding upstream version 6.4.3+dfsg1.upstream/6.4.3+dfsg1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

36 files changed, 6045 insertions, 0 deletions

diff --git a/wp-includes/customize/class-wp-customize-background-image-control.php b/wp-includes/customize/class-wp-customize-background-image-control.php
new file mode 100644
index 0000000..e6b3ca6
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-background-image-control.php
@@ -0,0 +1,66 @@
+<?php
+/**
+ * Customize API: WP_Customize_Background_Image_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Background Image Control class.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Image_Control
+ */
+class WP_Customize_Background_Image_Control extends WP_Customize_Image_Control {
+
+	/**
+	 * Customize control type.
+	 *
+	 * @since 4.1.0
+	 * @var string
+	 */
+	public $type = 'background';
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 3.4.0
+	 * @uses WP_Customize_Image_Control::__construct()
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 */
+	public function __construct( $manager ) {
+		parent::__construct(
+			$manager,
+			'background_image',
+			array(
+				'label'   => __( 'Background Image' ),
+				'section' => 'background_image',
+			)
+		);
+	}
+
+	/**
+	 * Enqueue control related scripts/styles.
+	 *
+	 * @since 4.1.0
+	 */
+	public function enqueue() {
+		parent::enqueue();
+
+		$custom_background = get_theme_support( 'custom-background' );
+		wp_localize_script(
+			'customize-controls',
+			'_wpCustomizeBackground',
+			array(
+				'defaults' => ! empty( $custom_background[0] ) ? $custom_background[0] : array(),
+				'nonces'   => array(
+					'add' => wp_create_nonce( 'background-add' ),
+				),
+			)
+		);
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-background-image-setting.php b/wp-includes/customize/class-wp-customize-background-image-setting.php
new file mode 100644
index 0000000..f56810e
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-background-image-setting.php
@@ -0,0 +1,35 @@
+<?php
+/**
+ * Customize API: WP_Customize_Background_Image_Setting class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customizer Background Image Setting class.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Setting
+ */
+final class WP_Customize_Background_Image_Setting extends WP_Customize_Setting {
+
+	/**
+	 * Unique string identifier for the setting.
+	 *
+	 * @since 3.4.0
+	 * @var string
+	 */
+	public $id = 'background_image_thumb';
+
+	/**
+	 * @since 3.4.0
+	 *
+	 * @param mixed $value The value to update. Not used.
+	 */
+	public function update( $value ) {
+		remove_theme_mod( 'background_image_thumb' );
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-background-position-control.php b/wp-includes/customize/class-wp-customize-background-position-control.php
new file mode 100644
index 0000000..05802f5
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-background-position-control.php
@@ -0,0 +1,116 @@
+<?php
+/**
+ * Customize API: WP_Customize_Background_Position_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.7.0
+ */
+
+/**
+ * Customize Background Position Control class.
+ *
+ * @since 4.7.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Background_Position_Control extends WP_Customize_Control {
+
+	/**
+	 * Type.
+	 *
+	 * @since 4.7.0
+	 * @var string
+	 */
+	public $type = 'background_position';
+
+	/**
+	 * Don't render the control content from PHP, as it's rendered via JS on load.
+	 *
+	 * @since 4.7.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * Render a JS template for the content of the position control.
+	 *
+	 * @since 4.7.0
+	 */
+	public function content_template() {
+		$options = array(
+			array(
+				'left top'   => array(
+					'label' => __( 'Top Left' ),
+					'icon'  => 'dashicons dashicons-arrow-left-alt',
+				),
+				'center top' => array(
+					'label' => __( 'Top' ),
+					'icon'  => 'dashicons dashicons-arrow-up-alt',
+				),
+				'right top'  => array(
+					'label' => __( 'Top Right' ),
+					'icon'  => 'dashicons dashicons-arrow-right-alt',
+				),
+			),
+			array(
+				'left center'   => array(
+					'label' => __( 'Left' ),
+					'icon'  => 'dashicons dashicons-arrow-left-alt',
+				),
+				'center center' => array(
+					'label' => __( 'Center' ),
+					'icon'  => 'background-position-center-icon',
+				),
+				'right center'  => array(
+					'label' => __( 'Right' ),
+					'icon'  => 'dashicons dashicons-arrow-right-alt',
+				),
+			),
+			array(
+				'left bottom'   => array(
+					'label' => __( 'Bottom Left' ),
+					'icon'  => 'dashicons dashicons-arrow-left-alt',
+				),
+				'center bottom' => array(
+					'label' => __( 'Bottom' ),
+					'icon'  => 'dashicons dashicons-arrow-down-alt',
+				),
+				'right bottom'  => array(
+					'label' => __( 'Bottom Right' ),
+					'icon'  => 'dashicons dashicons-arrow-right-alt',
+				),
+			),
+		);
+		?>
+		<# if ( data.label ) { #>
+			<span class="customize-control-title">{{{ data.label }}}</span>
+		<# } #>
+		<# if ( data.description ) { #>
+			<span class="description customize-control-description">{{{ data.description }}}</span>
+		<# } #>
+		<div class="customize-control-content">
+			<fieldset>
+				<legend class="screen-reader-text"><span>
+					<?php
+					/* translators: Hidden accessibility text. */
+					_e( 'Image Position' );
+					?>
+				</span></legend>
+				<div class="background-position-control">
+				<?php foreach ( $options as $group ) : ?>
+					<div class="button-group">
+					<?php foreach ( $group as $value => $input ) : ?>
+						<label>
+							<input class="ui-helper-hidden-accessible" name="background-position" type="radio" value="<?php echo esc_attr( $value ); ?>">
+							<span class="button display-options position"><span class="<?php echo esc_attr( $input['icon'] ); ?>" aria-hidden="true"></span></span>
+							<span class="screen-reader-text"><?php echo $input['label']; ?></span>
+						</label>
+					<?php endforeach; ?>
+					</div>
+				<?php endforeach; ?>
+				</div>
+			</fieldset>
+		</div>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-code-editor-control.php b/wp-includes/customize/class-wp-customize-code-editor-control.php
new file mode 100644
index 0000000..c22d6ea
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-code-editor-control.php
@@ -0,0 +1,111 @@
+<?php
+/**
+ * Customize API: WP_Customize_Code_Editor_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.9.0
+ */
+
+/**
+ * Customize Code Editor Control class.
+ *
+ * @since 4.9.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Code_Editor_Control extends WP_Customize_Control {
+
+	/**
+	 * Customize control type.
+	 *
+	 * @since 4.9.0
+	 * @var string
+	 */
+	public $type = 'code_editor';
+
+	/**
+	 * Type of code that is being edited.
+	 *
+	 * @since 4.9.0
+	 * @var string
+	 */
+	public $code_type = '';
+
+	/**
+	 * Code editor settings.
+	 *
+	 * @see wp_enqueue_code_editor()
+	 * @since 4.9.0
+	 * @var array|false
+	 */
+	public $editor_settings = array();
+
+	/**
+	 * Enqueue control related scripts/styles.
+	 *
+	 * @since 4.9.0
+	 */
+	public function enqueue() {
+		$this->editor_settings = wp_enqueue_code_editor(
+			array_merge(
+				array(
+					'type'       => $this->code_type,
+					'codemirror' => array(
+						'indentUnit' => 2,
+						'tabSize'    => 2,
+					),
+				),
+				$this->editor_settings
+			)
+		);
+	}
+
+	/**
+	 * Refresh the parameters passed to the JavaScript via JSON.
+	 *
+	 * @since 4.9.0
+	 *
+	 * @see WP_Customize_Control::json()
+	 *
+	 * @return array Array of parameters passed to the JavaScript.
+	 */
+	public function json() {
+		$json                    = parent::json();
+		$json['editor_settings'] = $this->editor_settings;
+		$json['input_attrs']     = $this->input_attrs;
+		return $json;
+	}
+
+	/**
+	 * Don't render the control content from PHP, as it's rendered via JS on load.
+	 *
+	 * @since 4.9.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * Render a JS template for control display.
+	 *
+	 * @since 4.9.0
+	 */
+	public function content_template() {
+		?>
+		<# var elementIdPrefix = 'el' + String( Math.random() ); #>
+		<# if ( data.label ) { #>
+			<label for="{{ elementIdPrefix }}_editor" class="customize-control-title">
+				{{ data.label }}
+			</label>
+		<# } #>
+		<# if ( data.description ) { #>
+			<span class="description customize-control-description">{{{ data.description }}}</span>
+		<# } #>
+		<div class="customize-control-notifications-container"></div>
+		<textarea id="{{ elementIdPrefix }}_editor"
+			<# _.each( _.extend( { 'class': 'code' }, data.input_attrs ), function( value, key ) { #>
+				{{{ key }}}="{{ value }}"
+			<# }); #>
+			></textarea>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-color-control.php b/wp-includes/customize/class-wp-customize-color-control.php
new file mode 100644
index 0000000..a164c6a
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-color-control.php
@@ -0,0 +1,122 @@
+<?php
+/**
+ * Customize API: WP_Customize_Color_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Color Control class.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Color_Control extends WP_Customize_Control {
+	/**
+	 * Type.
+	 *
+	 * @var string
+	 */
+	public $type = 'color';
+
+	/**
+	 * Statuses.
+	 *
+	 * @var array
+	 */
+	public $statuses;
+
+	/**
+	 * Mode.
+	 *
+	 * @since 4.7.0
+	 * @var string
+	 */
+	public $mode = 'full';
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 3.4.0
+	 *
+	 * @see WP_Customize_Control::__construct()
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      Control ID.
+	 * @param array                $args    Optional. Arguments to override class property defaults.
+	 *                                      See WP_Customize_Control::__construct() for information
+	 *                                      on accepted arguments. Default empty array.
+	 */
+	public function __construct( $manager, $id, $args = array() ) {
+		$this->statuses = array( '' => __( 'Default' ) );
+		parent::__construct( $manager, $id, $args );
+	}
+
+	/**
+	 * Enqueue scripts/styles for the color picker.
+	 *
+	 * @since 3.4.0
+	 */
+	public function enqueue() {
+		wp_enqueue_script( 'wp-color-picker' );
+		wp_enqueue_style( 'wp-color-picker' );
+	}
+
+	/**
+	 * Refresh the parameters passed to the JavaScript via JSON.
+	 *
+	 * @since 3.4.0
+	 * @uses WP_Customize_Control::to_json()
+	 */
+	public function to_json() {
+		parent::to_json();
+		$this->json['statuses']     = $this->statuses;
+		$this->json['defaultValue'] = $this->setting->default;
+		$this->json['mode']         = $this->mode;
+	}
+
+	/**
+	 * Don't render the control content from PHP, as it's rendered via JS on load.
+	 *
+	 * @since 3.4.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * Render a JS template for the content of the color picker control.
+	 *
+	 * @since 4.1.0
+	 */
+	public function content_template() {
+		?>
+		<# var defaultValue = '#RRGGBB', defaultValueAttr = '',
+			isHueSlider = data.mode === 'hue';
+		if ( data.defaultValue && _.isString( data.defaultValue ) && ! isHueSlider ) {
+			if ( '#' !== data.defaultValue.substring( 0, 1 ) ) {
+				defaultValue = '#' + data.defaultValue;
+			} else {
+				defaultValue = data.defaultValue;
+			}
+			defaultValueAttr = ' data-default-color=' + defaultValue; // Quotes added automatically.
+		} #>
+		<# if ( data.label ) { #>
+			<span class="customize-control-title">{{{ data.label }}}</span>
+		<# } #>
+		<# if ( data.description ) { #>
+			<span class="description customize-control-description">{{{ data.description }}}</span>
+		<# } #>
+		<div class="customize-control-content">
+			<label><span class="screen-reader-text">{{{ data.label }}}</span>
+			<# if ( isHueSlider ) { #>
+				<input class="color-picker-hue" type="text" data-type="hue" />
+			<# } else { #>
+				<input class="color-picker-hex" type="text" maxlength="7" placeholder="{{ defaultValue }}" {{ defaultValueAttr }} />
+			<# } #>
+			</label>
+		</div>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-cropped-image-control.php b/wp-includes/customize/class-wp-customize-cropped-image-control.php
new file mode 100644
index 0000000..5f0debb
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-cropped-image-control.php
@@ -0,0 +1,85 @@
+<?php
+/**
+ * Customize API: WP_Customize_Cropped_Image_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Cropped Image Control class.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Image_Control
+ */
+class WP_Customize_Cropped_Image_Control extends WP_Customize_Image_Control {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'cropped_image';
+
+	/**
+	 * Suggested width for cropped image.
+	 *
+	 * @since 4.3.0
+	 * @var int
+	 */
+	public $width = 150;
+
+	/**
+	 * Suggested height for cropped image.
+	 *
+	 * @since 4.3.0
+	 * @var int
+	 */
+	public $height = 150;
+
+	/**
+	 * Whether the width is flexible.
+	 *
+	 * @since 4.3.0
+	 * @var bool
+	 */
+	public $flex_width = false;
+
+	/**
+	 * Whether the height is flexible.
+	 *
+	 * @since 4.3.0
+	 * @var bool
+	 */
+	public $flex_height = false;
+
+	/**
+	 * Enqueue control related scripts/styles.
+	 *
+	 * @since 4.3.0
+	 */
+	public function enqueue() {
+		wp_enqueue_script( 'customize-views' );
+
+		parent::enqueue();
+	}
+
+	/**
+	 * Refresh the parameters passed to the JavaScript via JSON.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Control::to_json()
+	 */
+	public function to_json() {
+		parent::to_json();
+
+		$this->json['width']       = absint( $this->width );
+		$this->json['height']      = absint( $this->height );
+		$this->json['flex_width']  = absint( $this->flex_width );
+		$this->json['flex_height'] = absint( $this->flex_height );
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-custom-css-setting.php b/wp-includes/customize/class-wp-customize-custom-css-setting.php
new file mode 100644
index 0000000..0e6132f
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-custom-css-setting.php
@@ -0,0 +1,212 @@
+<?php
+/**
+ * Customize API: WP_Customize_Custom_CSS_Setting class
+ *
+ * This handles validation, sanitization and saving of the value.
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.7.0
+ */
+
+/**
+ * Custom Setting to handle WP Custom CSS.
+ *
+ * @since 4.7.0
+ *
+ * @see WP_Customize_Setting
+ */
+final class WP_Customize_Custom_CSS_Setting extends WP_Customize_Setting {
+
+	/**
+	 * The setting type.
+	 *
+	 * @since 4.7.0
+	 * @var string
+	 */
+	public $type = 'custom_css';
+
+	/**
+	 * Setting Transport
+	 *
+	 * @since 4.7.0
+	 * @var string
+	 */
+	public $transport = 'postMessage';
+
+	/**
+	 * Capability required to edit this setting.
+	 *
+	 * @since 4.7.0
+	 * @var string
+	 */
+	public $capability = 'edit_css';
+
+	/**
+	 * Stylesheet
+	 *
+	 * @since 4.7.0
+	 * @var string
+	 */
+	public $stylesheet = '';
+
+	/**
+	 * WP_Customize_Custom_CSS_Setting constructor.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @throws Exception If the setting ID does not match the pattern `custom_css[$stylesheet]`.
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      A specific ID of the setting.
+	 *                                      Can be a theme mod or option name.
+	 * @param array                $args    Setting arguments.
+	 */
+	public function __construct( $manager, $id, $args = array() ) {
+		parent::__construct( $manager, $id, $args );
+		if ( 'custom_css' !== $this->id_data['base'] ) {
+			throw new Exception( 'Expected custom_css id_base.' );
+		}
+		if ( 1 !== count( $this->id_data['keys'] ) || empty( $this->id_data['keys'][0] ) ) {
+			throw new Exception( 'Expected single stylesheet key.' );
+		}
+		$this->stylesheet = $this->id_data['keys'][0];
+	}
+
+	/**
+	 * Add filter to preview post value.
+	 *
+	 * @since 4.7.9
+	 *
+	 * @return bool False when preview short-circuits due no change needing to be previewed.
+	 */
+	public function preview() {
+		if ( $this->is_previewed ) {
+			return false;
+		}
+		$this->is_previewed = true;
+		add_filter( 'wp_get_custom_css', array( $this, 'filter_previewed_wp_get_custom_css' ), 9, 2 );
+		return true;
+	}
+
+	/**
+	 * Filters `wp_get_custom_css` for applying the customized value.
+	 *
+	 * This is used in the preview when `wp_get_custom_css()` is called for rendering the styles.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @see wp_get_custom_css()
+	 *
+	 * @param string $css        Original CSS.
+	 * @param string $stylesheet Current stylesheet.
+	 * @return string CSS.
+	 */
+	public function filter_previewed_wp_get_custom_css( $css, $stylesheet ) {
+		if ( $stylesheet === $this->stylesheet ) {
+			$customized_value = $this->post_value( null );
+			if ( ! is_null( $customized_value ) ) {
+				$css = $customized_value;
+			}
+		}
+		return $css;
+	}
+
+	/**
+	 * Fetch the value of the setting. Will return the previewed value when `preview()` is called.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @see WP_Customize_Setting::value()
+	 *
+	 * @return string
+	 */
+	public function value() {
+		if ( $this->is_previewed ) {
+			$post_value = $this->post_value( null );
+			if ( null !== $post_value ) {
+				return $post_value;
+			}
+		}
+		$id_base = $this->id_data['base'];
+		$value   = '';
+		$post    = wp_get_custom_css_post( $this->stylesheet );
+		if ( $post ) {
+			$value = $post->post_content;
+		}
+		if ( empty( $value ) ) {
+			$value = $this->default;
+		}
+
+		/** This filter is documented in wp-includes/class-wp-customize-setting.php */
+		$value = apply_filters( "customize_value_{$id_base}", $value, $this );
+
+		return $value;
+	}
+
+	/**
+	 * Validate a received value for being valid CSS.
+	 *
+	 * Checks for imbalanced braces, brackets, and comments.
+	 * Notifications are rendered when the customizer state is saved.
+	 *
+	 * @since 4.7.0
+	 * @since 4.9.0 Checking for balanced characters has been moved client-side via linting in code editor.
+	 * @since 5.9.0 Renamed `$css` to `$value` for PHP 8 named parameter support.
+	 *
+	 * @param string $value CSS to validate.
+	 * @return true|WP_Error True if the input was validated, otherwise WP_Error.
+	 */
+	public function validate( $value ) {
+		// Restores the more descriptive, specific name for use within this method.
+		$css = $value;
+
+		$validity = new WP_Error();
+
+		if ( preg_match( '#</?\w+#', $css ) ) {
+			$validity->add( 'illegal_markup', __( 'Markup is not allowed in CSS.' ) );
+		}
+
+		if ( ! $validity->has_errors() ) {
+			$validity = parent::validate( $css );
+		}
+		return $validity;
+	}
+
+	/**
+	 * Store the CSS setting value in the custom_css custom post type for the stylesheet.
+	 *
+	 * @since 4.7.0
+	 * @since 5.9.0 Renamed `$css` to `$value` for PHP 8 named parameter support.
+	 *
+	 * @param string $value CSS to update.
+	 * @return int|false The post ID or false if the value could not be saved.
+	 */
+	public function update( $value ) {
+		// Restores the more descriptive, specific name for use within this method.
+		$css = $value;
+
+		if ( empty( $css ) ) {
+			$css = '';
+		}
+
+		$r = wp_update_custom_css_post(
+			$css,
+			array(
+				'stylesheet' => $this->stylesheet,
+			)
+		);
+
+		if ( $r instanceof WP_Error ) {
+			return false;
+		}
+		$post_id = $r->ID;
+
+		// Cache post ID in theme mod for performance to avoid additional DB query.
+		if ( $this->manager->get_stylesheet() === $this->stylesheet ) {
+			set_theme_mod( 'custom_css_post_id', $post_id );
+		}
+
+		return $post_id;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-date-time-control.php b/wp-includes/customize/class-wp-customize-date-time-control.php
new file mode 100644
index 0000000..1b445af
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-date-time-control.php
@@ -0,0 +1,319 @@
+<?php
+/**
+ * Customize API: WP_Customize_Date_Time_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.9.0
+ */
+
+/**
+ * Customize Date Time Control class.
+ *
+ * @since 4.9.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Date_Time_Control extends WP_Customize_Control {
+
+	/**
+	 * Customize control type.
+	 *
+	 * @since 4.9.0
+	 * @var string
+	 */
+	public $type = 'date_time';
+
+	/**
+	 * Minimum Year.
+	 *
+	 * @since 4.9.0
+	 * @var int
+	 */
+	public $min_year = 1000;
+
+	/**
+	 * Maximum Year.
+	 *
+	 * @since 4.9.0
+	 * @var int
+	 */
+	public $max_year = 9999;
+
+	/**
+	 * Allow past date, if set to false user can only select future date.
+	 *
+	 * @since 4.9.0
+	 * @var bool
+	 */
+	public $allow_past_date = true;
+
+	/**
+	 * Whether hours, minutes, and meridian should be shown.
+	 *
+	 * @since 4.9.0
+	 * @var bool
+	 */
+	public $include_time = true;
+
+	/**
+	 * If set to false the control will appear in 24 hour format,
+	 * the value will still be saved in Y-m-d H:i:s format.
+	 *
+	 * @since 4.9.0
+	 * @var bool
+	 */
+	public $twelve_hour_format = true;
+
+	/**
+	 * Don't render the control's content - it's rendered with a JS template.
+	 *
+	 * @since 4.9.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * Export data to JS.
+	 *
+	 * @since 4.9.0
+	 * @return array
+	 */
+	public function json() {
+		$data = parent::json();
+
+		$data['maxYear']          = (int) $this->max_year;
+		$data['minYear']          = (int) $this->min_year;
+		$data['allowPastDate']    = (bool) $this->allow_past_date;
+		$data['twelveHourFormat'] = (bool) $this->twelve_hour_format;
+		$data['includeTime']      = (bool) $this->include_time;
+
+		return $data;
+	}
+
+	/**
+	 * Renders a JS template for the content of date time control.
+	 *
+	 * @since 4.9.0
+	 */
+	public function content_template() {
+		$data          = array_merge( $this->json(), $this->get_month_choices() );
+		$timezone_info = $this->get_timezone_info();
+
+		$date_format = get_option( 'date_format' );
+		$date_format = preg_replace( '/(?<!\\\\)[Yyo]/', '%1$s', $date_format );
+		$date_format = preg_replace( '/(?<!\\\\)[FmMn]/', '%2$s', $date_format );
+		$date_format = preg_replace( '/(?<!\\\\)[jd]/', '%3$s', $date_format );
+
+		// Fallback to ISO date format if year, month, or day are missing from the date format.
+		if ( 1 !== substr_count( $date_format, '%1$s' ) || 1 !== substr_count( $date_format, '%2$s' ) || 1 !== substr_count( $date_format, '%3$s' ) ) {
+			$date_format = '%1$s-%2$s-%3$s';
+		}
+		?>
+
+		<# _.defaults( data, <?php echo wp_json_encode( $data ); ?> ); #>
+		<# var idPrefix = _.uniqueId( 'el' ) + '-'; #>
+
+		<# if ( data.label ) { #>
+			<span class="customize-control-title">
+				{{ data.label }}
+			</span>
+		<# } #>
+		<div class="customize-control-notifications-container"></div>
+		<# if ( data.description ) { #>
+			<span class="description customize-control-description">{{ data.description }}</span>
+		<# } #>
+		<div class="date-time-fields {{ data.includeTime ? 'includes-time' : '' }}">
+			<fieldset class="day-row">
+				<legend class="title-day {{ ! data.includeTime ? 'screen-reader-text' : '' }}"><?php esc_html_e( 'Date' ); ?></legend>
+				<div class="day-fields clear">
+					<?php ob_start(); ?>
+					<label for="{{ idPrefix }}date-time-month" class="screen-reader-text">
+						<?php
+						/* translators: Hidden accessibility text. */
+						esc_html_e( 'Month' );
+						?>
+					</label>
+					<select id="{{ idPrefix }}date-time-month" class="date-input month" data-component="month">
+						<# _.each( data.month_choices, function( choice ) {
+							if ( _.isObject( choice ) && ! _.isUndefined( choice.text ) && ! _.isUndefined( choice.value ) ) {
+								text = choice.text;
+								value = choice.value;
+							}
+							#>
+							<option value="{{ value }}" >
+								{{ text }}
+							</option>
+						<# } ); #>
+					</select>
+					<?php $month_field = trim( ob_get_clean() ); ?>
+
+					<?php ob_start(); ?>
+					<label for="{{ idPrefix }}date-time-day" class="screen-reader-text">
+						<?php
+						/* translators: Hidden accessibility text. */
+						esc_html_e( 'Day' );
+						?>
+					</label>
+					<input id="{{ idPrefix }}date-time-day" type="number" size="2" autocomplete="off" class="date-input day" data-component="day" min="1" max="31" />
+					<?php $day_field = trim( ob_get_clean() ); ?>
+
+					<?php ob_start(); ?>
+					<label for="{{ idPrefix }}date-time-year" class="screen-reader-text">
+						<?php
+						/* translators: Hidden accessibility text. */
+						esc_html_e( 'Year' );
+						?>
+					</label>
+					<input id="{{ idPrefix }}date-time-year" type="number" size="4" autocomplete="off" class="date-input year" data-component="year" min="{{ data.minYear }}" max="{{ data.maxYear }}">
+					<?php $year_field = trim( ob_get_clean() ); ?>
+
+					<?php printf( $date_format, $year_field, $month_field, $day_field ); ?>
+				</div>
+			</fieldset>
+			<# if ( data.includeTime ) { #>
+				<fieldset class="time-row clear">
+					<legend class="title-time"><?php esc_html_e( 'Time' ); ?></legend>
+					<div class="time-fields clear">
+						<label for="{{ idPrefix }}date-time-hour" class="screen-reader-text">
+							<?php
+							/* translators: Hidden accessibility text. */
+							esc_html_e( 'Hour' );
+							?>
+						</label>
+						<# var maxHour = data.twelveHourFormat ? 12 : 23; #>
+						<# var minHour = data.twelveHourFormat ? 1 : 0; #>
+						<input id="{{ idPrefix }}date-time-hour" type="number" size="2" autocomplete="off" class="date-input hour" data-component="hour" min="{{ minHour }}" max="{{ maxHour }}">
+						:
+						<label for="{{ idPrefix }}date-time-minute" class="screen-reader-text">
+							<?php
+							/* translators: Hidden accessibility text. */
+							esc_html_e( 'Minute' );
+							?>
+						</label>
+						<input id="{{ idPrefix }}date-time-minute" type="number" size="2" autocomplete="off" class="date-input minute" data-component="minute" min="0" max="59">
+						<# if ( data.twelveHourFormat ) { #>
+							<label for="{{ idPrefix }}date-time-meridian" class="screen-reader-text">
+								<?php
+								/* translators: Hidden accessibility text. */
+								esc_html_e( 'Meridian' );
+								?>
+							</label>
+							<select id="{{ idPrefix }}date-time-meridian" class="date-input meridian" data-component="meridian">
+								<option value="am"><?php esc_html_e( 'AM' ); ?></option>
+								<option value="pm"><?php esc_html_e( 'PM' ); ?></option>
+							</select>
+						<# } #>
+						<p><?php echo $timezone_info['description']; ?></p>
+					</div>
+				</fieldset>
+			<# } #>
+		</div>
+		<?php
+	}
+
+	/**
+	 * Generate options for the month Select.
+	 *
+	 * Based on touch_time().
+	 *
+	 * @since 4.9.0
+	 *
+	 * @see touch_time()
+	 *
+	 * @global WP_Locale $wp_locale WordPress date and time locale object.
+	 *
+	 * @return array
+	 */
+	public function get_month_choices() {
+		global $wp_locale;
+		$months = array();
+		for ( $i = 1; $i < 13; $i++ ) {
+			$month_text = $wp_locale->get_month_abbrev( $wp_locale->get_month( $i ) );
+
+			/* translators: 1: Month number (01, 02, etc.), 2: Month abbreviation. */
+			$months[ $i ]['text']  = sprintf( __( '%1$s-%2$s' ), $i, $month_text );
+			$months[ $i ]['value'] = $i;
+		}
+		return array(
+			'month_choices' => $months,
+		);
+	}
+
+	/**
+	 * Get timezone info.
+	 *
+	 * @since 4.9.0
+	 *
+	 * @return array {
+	 *     Timezone info. All properties are optional.
+	 *
+	 *     @type string $abbr        Timezone abbreviation. Examples: PST or CEST.
+	 *     @type string $description Human-readable timezone description as HTML.
+	 * }
+	 */
+	public function get_timezone_info() {
+		$tz_string     = get_option( 'timezone_string' );
+		$timezone_info = array();
+
+		if ( $tz_string ) {
+			try {
+				$tz = new DateTimeZone( $tz_string );
+			} catch ( Exception $e ) {
+				$tz = '';
+			}
+
+			if ( $tz ) {
+				$now                   = new DateTime( 'now', $tz );
+				$formatted_gmt_offset  = $this->format_gmt_offset( $tz->getOffset( $now ) / HOUR_IN_SECONDS );
+				$tz_name               = str_replace( '_', ' ', $tz->getName() );
+				$timezone_info['abbr'] = $now->format( 'T' );
+
+				$timezone_info['description'] = sprintf(
+					/* translators: 1: Timezone name, 2: Timezone abbreviation, 3: UTC abbreviation and offset, 4: UTC offset. */
+					__( 'Your timezone is set to %1$s (%2$s), currently %3$s (Coordinated Universal Time %4$s).' ),
+					$tz_name,
+					'<abbr>' . $timezone_info['abbr'] . '</abbr>',
+					'<abbr>UTC</abbr>' . $formatted_gmt_offset,
+					$formatted_gmt_offset
+				);
+			} else {
+				$timezone_info['description'] = '';
+			}
+		} else {
+			$formatted_gmt_offset = $this->format_gmt_offset( (int) get_option( 'gmt_offset', 0 ) );
+
+			$timezone_info['description'] = sprintf(
+				/* translators: 1: UTC abbreviation and offset, 2: UTC offset. */
+				__( 'Your timezone is set to %1$s (Coordinated Universal Time %2$s).' ),
+				'<abbr>UTC</abbr>' . $formatted_gmt_offset,
+				$formatted_gmt_offset
+			);
+		}
+
+		return $timezone_info;
+	}
+
+	/**
+	 * Format GMT Offset.
+	 *
+	 * @since 4.9.0
+	 *
+	 * @see wp_timezone_choice()
+	 *
+	 * @param float $offset Offset in hours.
+	 * @return string Formatted offset.
+	 */
+	public function format_gmt_offset( $offset ) {
+		if ( 0 <= $offset ) {
+			$formatted_offset = '+' . (string) $offset;
+		} else {
+			$formatted_offset = (string) $offset;
+		}
+		$formatted_offset = str_replace(
+			array( '.25', '.5', '.75' ),
+			array( ':15', ':30', ':45' ),
+			$formatted_offset
+		);
+		return $formatted_offset;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-filter-setting.php b/wp-includes/customize/class-wp-customize-filter-setting.php
new file mode 100644
index 0000000..ad70f4f
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-filter-setting.php
@@ -0,0 +1,29 @@
+<?php
+/**
+ * Customize API: WP_Customize_Filter_Setting class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * A setting that is used to filter a value, but will not save the results.
+ *
+ * Results should be properly handled using another setting or callback.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Setting
+ */
+class WP_Customize_Filter_Setting extends WP_Customize_Setting {
+
+	/**
+	 * Saves the value of the setting, using the related API.
+	 *
+	 * @since 3.4.0
+	 *
+	 * @param mixed $value The value to update.
+	 */
+	public function update( $value ) {}
+}
diff --git a/wp-includes/customize/class-wp-customize-header-image-control.php b/wp-includes/customize/class-wp-customize-header-image-control.php
new file mode 100644
index 0000000..ecb134a
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-header-image-control.php
@@ -0,0 +1,271 @@
+<?php
+/**
+ * Customize API: WP_Customize_Header_Image_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Header Image Control class.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Image_Control
+ */
+class WP_Customize_Header_Image_Control extends WP_Customize_Image_Control {
+
+	/**
+	 * Customize control type.
+	 *
+	 * @since 4.2.0
+	 * @var string
+	 */
+	public $type = 'header';
+
+	/**
+	 * Uploaded header images.
+	 *
+	 * @since 3.9.0
+	 * @var string
+	 */
+	public $uploaded_headers;
+
+	/**
+	 * Default header images.
+	 *
+	 * @since 3.9.0
+	 * @var string
+	 */
+	public $default_headers;
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 3.4.0
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 */
+	public function __construct( $manager ) {
+		parent::__construct(
+			$manager,
+			'header_image',
+			array(
+				'label'    => __( 'Header Image' ),
+				'settings' => array(
+					'default' => 'header_image',
+					'data'    => 'header_image_data',
+				),
+				'section'  => 'header_image',
+				'removed'  => 'remove-header',
+				'get_url'  => 'get_header_image',
+			)
+		);
+	}
+
+	/**
+	 */
+	public function enqueue() {
+		wp_enqueue_media();
+		wp_enqueue_script( 'customize-views' );
+
+		$this->prepare_control();
+
+		wp_localize_script(
+			'customize-views',
+			'_wpCustomizeHeader',
+			array(
+				'data'     => array(
+					'width'         => absint( get_theme_support( 'custom-header', 'width' ) ),
+					'height'        => absint( get_theme_support( 'custom-header', 'height' ) ),
+					'flex-width'    => absint( get_theme_support( 'custom-header', 'flex-width' ) ),
+					'flex-height'   => absint( get_theme_support( 'custom-header', 'flex-height' ) ),
+					'currentImgSrc' => $this->get_current_image_src(),
+				),
+				'nonces'   => array(
+					'add'    => wp_create_nonce( 'header-add' ),
+					'remove' => wp_create_nonce( 'header-remove' ),
+				),
+				'uploads'  => $this->uploaded_headers,
+				'defaults' => $this->default_headers,
+			)
+		);
+
+		parent::enqueue();
+	}
+
+	/**
+	 * @global Custom_Image_Header $custom_image_header
+	 */
+	public function prepare_control() {
+		global $custom_image_header;
+		if ( empty( $custom_image_header ) ) {
+			return;
+		}
+
+		add_action( 'customize_controls_print_footer_scripts', array( $this, 'print_header_image_template' ) );
+
+		// Process default headers and uploaded headers.
+		$custom_image_header->process_default_headers();
+		$this->default_headers  = $custom_image_header->get_default_header_images();
+		$this->uploaded_headers = $custom_image_header->get_uploaded_header_images();
+	}
+
+	/**
+	 */
+	public function print_header_image_template() {
+		?>
+		<script type="text/template" id="tmpl-header-choice">
+			<# if (data.random) { #>
+			<button type="button" class="button display-options random">
+				<span class="dashicons dashicons-randomize dice"></span>
+				<# if ( data.type === 'uploaded' ) { #>
+					<?php _e( 'Randomize uploaded headers' ); ?>
+				<# } else if ( data.type === 'default' ) { #>
+					<?php _e( 'Randomize suggested headers' ); ?>
+				<# } #>
+			</button>
+
+			<# } else { #>
+
+			<button type="button" class="choice thumbnail"
+				data-customize-image-value="{{data.header.url}}"
+				data-customize-header-image-data="{{JSON.stringify(data.header)}}">
+				<span class="screen-reader-text">
+					<?php
+					/* translators: Hidden accessibility text. */
+					_e( 'Set image' );
+					?>
+				</span>
+				<img src="{{data.header.thumbnail_url}}" alt="{{data.header.alt_text || data.header.description}}" />
+			</button>
+
+			<# if ( data.type === 'uploaded' ) { #>
+				<button type="button" class="dashicons dashicons-no close">
+					<span class="screen-reader-text">
+						<?php
+						/* translators: Hidden accessibility text. */
+						_e( 'Remove image' );
+						?>
+					</span>
+				</button>
+			<# } #>
+
+			<# } #>
+		</script>
+
+		<script type="text/template" id="tmpl-header-current">
+			<# if (data.choice) { #>
+				<# if (data.random) { #>
+
+			<div class="placeholder">
+				<span class="dashicons dashicons-randomize dice"></span>
+				<# if ( data.type === 'uploaded' ) { #>
+					<?php _e( 'Randomizing uploaded headers' ); ?>
+				<# } else if ( data.type === 'default' ) { #>
+					<?php _e( 'Randomizing suggested headers' ); ?>
+				<# } #>
+			</div>
+
+				<# } else { #>
+
+			<img src="{{data.header.thumbnail_url}}" alt="{{data.header.alt_text || data.header.description}}" />
+
+				<# } #>
+			<# } else { #>
+
+			<div class="placeholder">
+				<?php _e( 'No image set' ); ?>
+			</div>
+
+			<# } #>
+		</script>
+		<?php
+	}
+
+	/**
+	 * @return string|void
+	 */
+	public function get_current_image_src() {
+		$src = $this->value();
+		if ( isset( $this->get_url ) ) {
+			$src = call_user_func( $this->get_url, $src );
+			return $src;
+		}
+	}
+
+	/**
+	 */
+	public function render_content() {
+		$visibility = $this->get_current_image_src() ? '' : ' style="display:none" ';
+		$width      = absint( get_theme_support( 'custom-header', 'width' ) );
+		$height     = absint( get_theme_support( 'custom-header', 'height' ) );
+		?>
+		<div class="customize-control-content">
+			<?php
+			if ( current_theme_supports( 'custom-header', 'video' ) ) {
+				echo '<span class="customize-control-title">' . $this->label . '</span>';
+			}
+			?>
+			<div class="customize-control-notifications-container"></div>
+			<p class="customizer-section-intro customize-control-description">
+				<?php
+				if ( current_theme_supports( 'custom-header', 'video' ) ) {
+					_e( 'Click &#8220;Add New Image&#8221; to upload an image file from your computer. Your theme works best with an image that matches the size of your video &#8212; you&#8217;ll be able to crop your image once you upload it for a perfect fit.' );
+				} elseif ( $width && $height ) {
+					printf(
+						/* translators: %s: Header size in pixels. */
+						__( 'Click &#8220;Add New Image&#8221; to upload an image file from your computer. Your theme works best with an image with a header size of %s pixels &#8212; you&#8217;ll be able to crop your image once you upload it for a perfect fit.' ),
+						sprintf( '<strong>%s &times; %s</strong>', $width, $height )
+					);
+				} elseif ( $width ) {
+					printf(
+						/* translators: %s: Header width in pixels. */
+						__( 'Click &#8220;Add New Image&#8221; to upload an image file from your computer. Your theme works best with an image with a header width of %s pixels &#8212; you&#8217;ll be able to crop your image once you upload it for a perfect fit.' ),
+						sprintf( '<strong>%s</strong>', $width )
+					);
+				} else {
+					printf(
+						/* translators: %s: Header height in pixels. */
+						__( 'Click &#8220;Add New Image&#8221; to upload an image file from your computer. Your theme works best with an image with a header height of %s pixels &#8212; you&#8217;ll be able to crop your image once you upload it for a perfect fit.' ),
+						sprintf( '<strong>%s</strong>', $height )
+					);
+				}
+				?>
+			</p>
+			<div class="current">
+				<label for="header_image-button">
+					<span class="customize-control-title">
+						<?php _e( 'Current header' ); ?>
+					</span>
+				</label>
+				<div class="container">
+				</div>
+			</div>
+			<div class="actions">
+				<?php if ( current_user_can( 'upload_files' ) ) : ?>
+				<button type="button"<?php echo $visibility; ?> class="button remove" aria-label="<?php esc_attr_e( 'Hide header image' ); ?>"><?php _e( 'Hide image' ); ?></button>
+				<button type="button" class="button new" id="header_image-button" aria-label="<?php esc_attr_e( 'Add New Header Image' ); ?>"><?php _e( 'Add New Image' ); ?></button>
+				<?php endif; ?>
+			</div>
+			<div class="choices">
+				<span class="customize-control-title header-previously-uploaded">
+					<?php _ex( 'Previously uploaded', 'custom headers' ); ?>
+				</span>
+				<div class="uploaded">
+					<div class="list">
+					</div>
+				</div>
+				<span class="customize-control-title header-default">
+					<?php _ex( 'Suggested', 'custom headers' ); ?>
+				</span>
+				<div class="default">
+					<div class="list">
+					</div>
+				</div>
+			</div>
+		</div>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-header-image-setting.php b/wp-includes/customize/class-wp-customize-header-image-setting.php
new file mode 100644
index 0000000..80333a5
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-header-image-setting.php
@@ -0,0 +1,62 @@
+<?php
+/**
+ * Customize API: WP_Customize_Header_Image_Setting class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * A setting that is used to filter a value, but will not save the results.
+ *
+ * Results should be properly handled using another setting or callback.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Setting
+ */
+final class WP_Customize_Header_Image_Setting extends WP_Customize_Setting {
+
+	/**
+	 * Unique string identifier for the setting.
+	 *
+	 * @since 3.4.0
+	 * @var string
+	 */
+	public $id = 'header_image_data';
+
+	/**
+	 * @since 3.4.0
+	 *
+	 * @global Custom_Image_Header $custom_image_header
+	 *
+	 * @param mixed $value The value to update.
+	 */
+	public function update( $value ) {
+		global $custom_image_header;
+
+		// If _custom_header_background_just_in_time() fails to initialize $custom_image_header when not is_admin().
+		if ( empty( $custom_image_header ) ) {
+			require_once ABSPATH . 'wp-admin/includes/class-custom-image-header.php';
+			$args                   = get_theme_support( 'custom-header' );
+			$admin_head_callback    = isset( $args[0]['admin-head-callback'] ) ? $args[0]['admin-head-callback'] : null;
+			$admin_preview_callback = isset( $args[0]['admin-preview-callback'] ) ? $args[0]['admin-preview-callback'] : null;
+			$custom_image_header    = new Custom_Image_Header( $admin_head_callback, $admin_preview_callback );
+		}
+
+		/*
+		 * If the value doesn't exist (removed or random),
+		 * use the header_image value.
+		 */
+		if ( ! $value ) {
+			$value = $this->manager->get_setting( 'header_image' )->post_value();
+		}
+
+		if ( is_array( $value ) && isset( $value['choice'] ) ) {
+			$custom_image_header->set_header_image( $value['choice'] );
+		} else {
+			$custom_image_header->set_header_image( $value );
+		}
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-image-control.php b/wp-includes/customize/class-wp-customize-image-control.php
new file mode 100644
index 0000000..03575d0
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-image-control.php
@@ -0,0 +1,72 @@
+<?php
+/**
+ * Customize API: WP_Customize_Image_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Image Control class.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Upload_Control
+ */
+class WP_Customize_Image_Control extends WP_Customize_Upload_Control {
+	/**
+	 * Control type.
+	 *
+	 * @since 3.4.0
+	 * @var string
+	 */
+	public $type = 'image';
+
+	/**
+	 * Media control mime type.
+	 *
+	 * @since 4.1.0
+	 * @var string
+	 */
+	public $mime_type = 'image';
+
+	/**
+	 * @since 3.4.2
+	 * @deprecated 4.1.0
+	 */
+	public function prepare_control() {}
+
+	/**
+	 * @since 3.4.0
+	 * @deprecated 4.1.0
+	 *
+	 * @param string $id
+	 * @param string $label
+	 * @param mixed  $callback
+	 */
+	public function add_tab( $id, $label, $callback ) {
+		_deprecated_function( __METHOD__, '4.1.0' );
+	}
+
+	/**
+	 * @since 3.4.0
+	 * @deprecated 4.1.0
+	 *
+	 * @param string $id
+	 */
+	public function remove_tab( $id ) {
+		_deprecated_function( __METHOD__, '4.1.0' );
+	}
+
+	/**
+	 * @since 3.4.0
+	 * @deprecated 4.1.0
+	 *
+	 * @param string $url
+	 * @param string $thumbnail_url
+	 */
+	public function print_tab_image( $url, $thumbnail_url = null ) {
+		_deprecated_function( __METHOD__, '4.1.0' );
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-media-control.php b/wp-includes/customize/class-wp-customize-media-control.php
new file mode 100644
index 0000000..f636892
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-media-control.php
@@ -0,0 +1,268 @@
+<?php
+/**
+ * Customize API: WP_Customize_Media_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Media Control class.
+ *
+ * @since 4.2.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Media_Control extends WP_Customize_Control {
+	/**
+	 * Control type.
+	 *
+	 * @since 4.2.0
+	 * @var string
+	 */
+	public $type = 'media';
+
+	/**
+	 * Media control mime type.
+	 *
+	 * @since 4.2.0
+	 * @var string
+	 */
+	public $mime_type = '';
+
+	/**
+	 * Button labels.
+	 *
+	 * @since 4.2.0
+	 * @var array
+	 */
+	public $button_labels = array();
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 4.1.0
+	 * @since 4.2.0 Moved from WP_Customize_Upload_Control.
+	 *
+	 * @see WP_Customize_Control::__construct()
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      Control ID.
+	 * @param array                $args    Optional. Arguments to override class property defaults.
+	 *                                      See WP_Customize_Control::__construct() for information
+	 *                                      on accepted arguments. Default empty array.
+	 */
+	public function __construct( $manager, $id, $args = array() ) {
+		parent::__construct( $manager, $id, $args );
+
+		$this->button_labels = wp_parse_args( $this->button_labels, $this->get_default_button_labels() );
+	}
+
+	/**
+	 * Enqueue control related scripts/styles.
+	 *
+	 * @since 3.4.0
+	 * @since 4.2.0 Moved from WP_Customize_Upload_Control.
+	 */
+	public function enqueue() {
+		wp_enqueue_media();
+	}
+
+	/**
+	 * Refresh the parameters passed to the JavaScript via JSON.
+	 *
+	 * @since 3.4.0
+	 * @since 4.2.0 Moved from WP_Customize_Upload_Control.
+	 *
+	 * @see WP_Customize_Control::to_json()
+	 */
+	public function to_json() {
+		parent::to_json();
+		$this->json['label']         = html_entity_decode( $this->label, ENT_QUOTES, get_bloginfo( 'charset' ) );
+		$this->json['mime_type']     = $this->mime_type;
+		$this->json['button_labels'] = $this->button_labels;
+		$this->json['canUpload']     = current_user_can( 'upload_files' );
+
+		$value = $this->value();
+
+		if ( is_object( $this->setting ) ) {
+			if ( $this->setting->default ) {
+				/*
+				 * Fake an attachment model - needs all fields used by template.
+				 * Note that the default value must be a URL, NOT an attachment ID.
+				 */
+				$ext  = substr( $this->setting->default, -3 );
+				$type = in_array( $ext, array( 'jpg', 'png', 'gif', 'bmp', 'webp' ), true ) ? 'image' : 'document';
+
+				$default_attachment = array(
+					'id'    => 1,
+					'url'   => $this->setting->default,
+					'type'  => $type,
+					'icon'  => wp_mime_type_icon( $type ),
+					'title' => wp_basename( $this->setting->default ),
+				);
+
+				if ( 'image' === $type ) {
+					$default_attachment['sizes'] = array(
+						'full' => array( 'url' => $this->setting->default ),
+					);
+				}
+
+				$this->json['defaultAttachment'] = $default_attachment;
+			}
+
+			if ( $value && $this->setting->default && $value === $this->setting->default ) {
+				// Set the default as the attachment.
+				$this->json['attachment'] = $this->json['defaultAttachment'];
+			} elseif ( $value ) {
+				$this->json['attachment'] = wp_prepare_attachment_for_js( $value );
+			}
+		}
+	}
+
+	/**
+	 * Don't render any content for this control from PHP.
+	 *
+	 * @since 3.4.0
+	 * @since 4.2.0 Moved from WP_Customize_Upload_Control.
+	 *
+	 * @see WP_Customize_Media_Control::content_template()
+	 */
+	public function render_content() {}
+
+	/**
+	 * Render a JS template for the content of the media control.
+	 *
+	 * @since 4.1.0
+	 * @since 4.2.0 Moved from WP_Customize_Upload_Control.
+	 */
+	public function content_template() {
+		?>
+		<#
+		var descriptionId = _.uniqueId( 'customize-media-control-description-' );
+		var describedByAttr = data.description ? ' aria-describedby="' + descriptionId + '" ' : '';
+		#>
+		<# if ( data.label ) { #>
+			<span class="customize-control-title">{{ data.label }}</span>
+		<# } #>
+		<div class="customize-control-notifications-container"></div>
+		<# if ( data.description ) { #>
+			<span id="{{ descriptionId }}" class="description customize-control-description">{{{ data.description }}}</span>
+		<# } #>
+
+		<# if ( data.attachment && data.attachment.id ) { #>
+			<div class="attachment-media-view attachment-media-view-{{ data.attachment.type }} {{ data.attachment.orientation }}">
+				<div class="thumbnail thumbnail-{{ data.attachment.type }}">
+					<# if ( 'image' === data.attachment.type && data.attachment.sizes && data.attachment.sizes.medium ) { #>
+						<img class="attachment-thumb" src="{{ data.attachment.sizes.medium.url }}" draggable="false" alt="" />
+					<# } else if ( 'image' === data.attachment.type && data.attachment.sizes && data.attachment.sizes.full ) { #>
+						<img class="attachment-thumb" src="{{ data.attachment.sizes.full.url }}" draggable="false" alt="" />
+					<# } else if ( 'audio' === data.attachment.type ) { #>
+						<# if ( data.attachment.image && data.attachment.image.src && data.attachment.image.src !== data.attachment.icon ) { #>
+							<img src="{{ data.attachment.image.src }}" class="thumbnail" draggable="false" alt="" />
+						<# } else { #>
+							<img src="{{ data.attachment.icon }}" class="attachment-thumb type-icon" draggable="false" alt="" />
+						<# } #>
+						<p class="attachment-meta attachment-meta-title">&#8220;{{ data.attachment.title }}&#8221;</p>
+						<# if ( data.attachment.album || data.attachment.meta.album ) { #>
+						<p class="attachment-meta"><em>{{ data.attachment.album || data.attachment.meta.album }}</em></p>
+						<# } #>
+						<# if ( data.attachment.artist || data.attachment.meta.artist ) { #>
+						<p class="attachment-meta">{{ data.attachment.artist || data.attachment.meta.artist }}</p>
+						<# } #>
+						<audio style="visibility: hidden" controls class="wp-audio-shortcode" width="100%" preload="none">
+							<source type="{{ data.attachment.mime }}" src="{{ data.attachment.url }}" />
+						</audio>
+					<# } else if ( 'video' === data.attachment.type ) { #>
+						<div class="wp-media-wrapper wp-video">
+							<video controls="controls" class="wp-video-shortcode" preload="metadata"
+								<# if ( data.attachment.image && data.attachment.image.src !== data.attachment.icon ) { #>poster="{{ data.attachment.image.src }}"<# } #>>
+								<source type="{{ data.attachment.mime }}" src="{{ data.attachment.url }}" />
+							</video>
+						</div>
+					<# } else { #>
+						<img class="attachment-thumb type-icon icon" src="{{ data.attachment.icon }}" draggable="false" alt="" />
+						<p class="attachment-title">{{ data.attachment.title }}</p>
+					<# } #>
+				</div>
+				<div class="actions">
+					<# if ( data.canUpload ) { #>
+					<button type="button" class="button remove-button">{{ data.button_labels.remove }}</button>
+					<button type="button" class="button upload-button control-focus" {{{ describedByAttr }}}>{{ data.button_labels.change }}</button>
+					<# } #>
+				</div>
+			</div>
+		<# } else { #>
+			<div class="attachment-media-view">
+				<# if ( data.canUpload ) { #>
+					<button type="button" class="upload-button button-add-media" {{{ describedByAttr }}}>{{ data.button_labels.select }}</button>
+				<# } #>
+				<div class="actions">
+					<# if ( data.defaultAttachment ) { #>
+						<button type="button" class="button default-button">{{ data.button_labels['default'] }}</button>
+					<# } #>
+				</div>
+			</div>
+		<# } #>
+		<?php
+	}
+
+	/**
+	 * Get default button labels.
+	 *
+	 * Provides an array of the default button labels based on the mime type of the current control.
+	 *
+	 * @since 4.9.0
+	 *
+	 * @return string[] An associative array of default button labels keyed by the button name.
+	 */
+	public function get_default_button_labels() {
+		// Get just the mime type and strip the mime subtype if present.
+		$mime_type = ! empty( $this->mime_type ) ? strtok( ltrim( $this->mime_type, '/' ), '/' ) : 'default';
+
+		switch ( $mime_type ) {
+			case 'video':
+				return array(
+					'select'       => __( 'Select video' ),
+					'change'       => __( 'Change video' ),
+					'default'      => __( 'Default' ),
+					'remove'       => __( 'Remove' ),
+					'placeholder'  => __( 'No video selected' ),
+					'frame_title'  => __( 'Select video' ),
+					'frame_button' => __( 'Choose video' ),
+				);
+			case 'audio':
+				return array(
+					'select'       => __( 'Select audio' ),
+					'change'       => __( 'Change audio' ),
+					'default'      => __( 'Default' ),
+					'remove'       => __( 'Remove' ),
+					'placeholder'  => __( 'No audio selected' ),
+					'frame_title'  => __( 'Select audio' ),
+					'frame_button' => __( 'Choose audio' ),
+				);
+			case 'image':
+				return array(
+					'select'       => __( 'Select image' ),
+					'site_icon'    => __( 'Select site icon' ),
+					'change'       => __( 'Change image' ),
+					'default'      => __( 'Default' ),
+					'remove'       => __( 'Remove' ),
+					'placeholder'  => __( 'No image selected' ),
+					'frame_title'  => __( 'Select image' ),
+					'frame_button' => __( 'Choose image' ),
+				);
+			default:
+				return array(
+					'select'       => __( 'Select file' ),
+					'change'       => __( 'Change file' ),
+					'default'      => __( 'Default' ),
+					'remove'       => __( 'Remove' ),
+					'placeholder'  => __( 'No file selected' ),
+					'frame_title'  => __( 'Select file' ),
+					'frame_button' => __( 'Choose file' ),
+				);
+		} // End switch().
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-auto-add-control.php b/wp-includes/customize/class-wp-customize-nav-menu-auto-add-control.php
new file mode 100644
index 0000000..c47fed4
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-auto-add-control.php
@@ -0,0 +1,51 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Auto_Add_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize control to represent the auto_add field for a given menu.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Nav_Menu_Auto_Add_Control extends WP_Customize_Control {
+
+	/**
+	 * Type of control, used by JS.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'nav_menu_auto_add';
+
+	/**
+	 * No-op since we're using JS template.
+	 *
+	 * @since 4.3.0
+	 */
+	protected function render_content() {}
+
+	/**
+	 * Render the Underscore template for this control.
+	 *
+	 * @since 4.3.0
+	 */
+	protected function content_template() {
+		?>
+		<# var elementId = _.uniqueId( 'customize-nav-menu-auto-add-control-' ); #>
+		<span class="customize-control-title"><?php _e( 'Menu Options' ); ?></span>
+		<span class="customize-inside-control-row">
+			<input id="{{ elementId }}" type="checkbox" class="auto_add" />
+			<label for="{{ elementId }}">
+				<?php _e( 'Automatically add new top-level pages to this menu' ); ?>
+			</label>
+		</span>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-control.php b/wp-includes/customize/class-wp-customize-nav-menu-control.php
new file mode 100644
index 0000000..7b2e439
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-control.php
@@ -0,0 +1,82 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Nav Menu Control Class.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Nav_Menu_Control extends WP_Customize_Control {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'nav_menu';
+
+	/**
+	 * Don't render the control's content - it uses a JS template instead.
+	 *
+	 * @since 4.3.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * JS/Underscore template for the control UI.
+	 *
+	 * @since 4.3.0
+	 */
+	public function content_template() {
+		$add_items = __( 'Add Items' );
+		?>
+		<p class="new-menu-item-invitation">
+			<?php
+			printf(
+				/* translators: %s: "Add Items" button text. */
+				__( 'Time to add some links! Click &#8220;%s&#8221; to start putting pages, categories, and custom links in your menu. Add as many things as you would like.' ),
+				$add_items
+			);
+			?>
+		</p>
+		<div class="customize-control-nav_menu-buttons">
+			<button type="button" class="button add-new-menu-item" aria-label="<?php esc_attr_e( 'Add or remove menu items' ); ?>" aria-expanded="false" aria-controls="available-menu-items">
+				<?php echo $add_items; ?>
+			</button>
+			<button type="button" class="button-link reorder-toggle" aria-label="<?php esc_attr_e( 'Reorder menu items' ); ?>" aria-describedby="reorder-items-desc-{{ data.menu_id }}">
+				<span class="reorder"><?php _e( 'Reorder' ); ?></span>
+				<span class="reorder-done"><?php _e( 'Done' ); ?></span>
+			</button>
+		</div>
+		<p class="screen-reader-text" id="reorder-items-desc-{{ data.menu_id }}">
+			<?php
+			/* translators: Hidden accessibility text. */
+			_e( 'When in reorder mode, additional controls to reorder menu items will be available in the items list above.' );
+			?>
+		</p>
+		<?php
+	}
+
+	/**
+	 * Return parameters for this control.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @return array Exported parameters.
+	 */
+	public function json() {
+		$exported            = parent::json();
+		$exported['menu_id'] = $this->setting->term_id;
+
+		return $exported;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-item-control.php b/wp-includes/customize/class-wp-customize-nav-menu-item-control.php
new file mode 100644
index 0000000..d6cae27
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-item-control.php
@@ -0,0 +1,181 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Item_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize control to represent the name field for a given menu.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Nav_Menu_Item_Control extends WP_Customize_Control {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'nav_menu_item';
+
+	/**
+	 * The nav menu item setting.
+	 *
+	 * @since 4.3.0
+	 * @var WP_Customize_Nav_Menu_Item_Setting
+	 */
+	public $setting;
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Control::__construct()
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      The control ID.
+	 * @param array                $args    Optional. Arguments to override class property defaults.
+	 *                                      See WP_Customize_Control::__construct() for information
+	 *                                      on accepted arguments. Default empty array.
+	 */
+	public function __construct( $manager, $id, $args = array() ) {
+		parent::__construct( $manager, $id, $args );
+	}
+
+	/**
+	 * Don't render the control's content - it's rendered with a JS template.
+	 *
+	 * @since 4.3.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * JS/Underscore template for the control UI.
+	 *
+	 * @since 4.3.0
+	 */
+	public function content_template() {
+		?>
+		<div class="menu-item-bar">
+			<div class="menu-item-handle">
+				<span class="item-type" aria-hidden="true">{{ data.item_type_label }}</span>
+				<span class="item-title" aria-hidden="true">
+					<span class="spinner"></span>
+					<span class="menu-item-title<# if ( ! data.title && ! data.original_title ) { #> no-title<# } #>">{{ data.title || data.original_title || wp.customize.Menus.data.l10n.untitled }}</span>
+				</span>
+				<span class="item-controls">
+					<button type="button" class="button-link item-edit" aria-expanded="false"><span class="screen-reader-text">
+					<?php
+						/* translators: 1: Title of a menu item, 2: Type of a menu item. */
+						printf( __( 'Edit menu item: %1$s (%2$s)' ), '{{ data.title || wp.customize.Menus.data.l10n.untitled }}', '{{ data.item_type_label }}' );
+					?>
+					</span><span class="toggle-indicator" aria-hidden="true"></span></button>
+					<button type="button" class="button-link item-delete submitdelete deletion"><span class="screen-reader-text">
+					<?php
+						/* translators: 1: Title of a menu item, 2: Type of a menu item. */
+						printf( __( 'Remove Menu Item: %1$s (%2$s)' ), '{{ data.title || wp.customize.Menus.data.l10n.untitled }}', '{{ data.item_type_label }}' );
+					?>
+					</span></button>
+				</span>
+			</div>
+		</div>
+
+		<div class="menu-item-settings" id="menu-item-settings-{{ data.menu_item_id }}">
+			<# if ( 'custom' === data.item_type ) { #>
+			<p class="field-url description description-thin">
+				<label for="edit-menu-item-url-{{ data.menu_item_id }}">
+					<?php _e( 'URL' ); ?><br />
+					<input class="widefat code edit-menu-item-url" type="text" id="edit-menu-item-url-{{ data.menu_item_id }}" name="menu-item-url" />
+				</label>
+			</p>
+		<# } #>
+			<p class="description description-thin">
+				<label for="edit-menu-item-title-{{ data.menu_item_id }}">
+					<?php _e( 'Navigation Label' ); ?><br />
+					<input type="text" id="edit-menu-item-title-{{ data.menu_item_id }}" placeholder="{{ data.original_title }}" class="widefat edit-menu-item-title" name="menu-item-title" />
+				</label>
+			</p>
+			<p class="field-link-target description description-thin">
+				<label for="edit-menu-item-target-{{ data.menu_item_id }}">
+					<input type="checkbox" id="edit-menu-item-target-{{ data.menu_item_id }}" class="edit-menu-item-target" value="_blank" name="menu-item-target" />
+					<?php _e( 'Open link in a new tab' ); ?>
+				</label>
+			</p>
+			<p class="field-title-attribute field-attr-title description description-thin">
+				<label for="edit-menu-item-attr-title-{{ data.menu_item_id }}">
+					<?php _e( 'Title Attribute' ); ?><br />
+					<input type="text" id="edit-menu-item-attr-title-{{ data.menu_item_id }}" class="widefat edit-menu-item-attr-title" name="menu-item-attr-title" />
+				</label>
+			</p>
+			<p class="field-css-classes description description-thin">
+				<label for="edit-menu-item-classes-{{ data.menu_item_id }}">
+					<?php _e( 'CSS Classes' ); ?><br />
+					<input type="text" id="edit-menu-item-classes-{{ data.menu_item_id }}" class="widefat code edit-menu-item-classes" name="menu-item-classes" />
+				</label>
+			</p>
+			<p class="field-xfn description description-thin">
+				<label for="edit-menu-item-xfn-{{ data.menu_item_id }}">
+					<?php _e( 'Link Relationship (XFN)' ); ?><br />
+					<input type="text" id="edit-menu-item-xfn-{{ data.menu_item_id }}" class="widefat code edit-menu-item-xfn" name="menu-item-xfn" />
+				</label>
+			</p>
+			<p class="field-description description description-thin">
+				<label for="edit-menu-item-description-{{ data.menu_item_id }}">
+					<?php _e( 'Description' ); ?><br />
+					<textarea id="edit-menu-item-description-{{ data.menu_item_id }}" class="widefat edit-menu-item-description" rows="3" cols="20" name="menu-item-description">{{ data.description }}</textarea>
+					<span class="description"><?php _e( 'The description will be displayed in the menu if the active theme supports it.' ); ?></span>
+				</label>
+			</p>
+
+			<?php
+			/**
+			 * Fires at the end of the form field template for nav menu items in the customizer.
+			 *
+			 * Additional fields can be rendered here and managed in JavaScript.
+			 *
+			 * @since 5.4.0
+			 */
+			do_action( 'wp_nav_menu_item_custom_fields_customize_template' );
+			?>
+
+			<div class="menu-item-actions description-thin submitbox">
+				<# if ( ( 'post_type' === data.item_type || 'taxonomy' === data.item_type ) && '' !== data.original_title ) { #>
+				<p class="link-to-original">
+					<?php
+						/* translators: Nav menu item original title. %s: Original title. */
+						printf( __( 'Original: %s' ), '<a class="original-link" href="{{ data.url }}">{{ data.original_title }}</a>' );
+					?>
+				</p>
+				<# } #>
+
+				<button type="button" class="button-link button-link-delete item-delete submitdelete deletion"><?php _e( 'Remove' ); ?></button>
+				<span class="spinner"></span>
+			</div>
+			<input type="hidden" name="menu-item-db-id[{{ data.menu_item_id }}]" class="menu-item-data-db-id" value="{{ data.menu_item_id }}" />
+			<input type="hidden" name="menu-item-parent-id[{{ data.menu_item_id }}]" class="menu-item-data-parent-id" value="{{ data.parent }}" />
+		</div><!-- .menu-item-settings-->
+		<ul class="menu-item-transport"></ul>
+		<?php
+	}
+
+	/**
+	 * Return parameters for this control.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @return array Exported parameters.
+	 */
+	public function json() {
+		$exported                 = parent::json();
+		$exported['menu_item_id'] = $this->setting->post_id;
+
+		return $exported;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php b/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php
new file mode 100644
index 0000000..4c8ad5b
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-item-setting.php
@@ -0,0 +1,905 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Item_Setting class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Setting to represent a nav_menu.
+ *
+ * Subclass of WP_Customize_Setting to represent a nav_menu taxonomy term, and
+ * the IDs for the nav_menu_items associated with the nav menu.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Setting
+ */
+class WP_Customize_Nav_Menu_Item_Setting extends WP_Customize_Setting {
+
+	const ID_PATTERN = '/^nav_menu_item\[(?P<id>-?\d+)\]$/';
+
+	const POST_TYPE = 'nav_menu_item';
+
+	const TYPE = 'nav_menu_item';
+
+	/**
+	 * Setting type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = self::TYPE;
+
+	/**
+	 * Default setting value.
+	 *
+	 * @since 4.3.0
+	 * @var array
+	 *
+	 * @see wp_setup_nav_menu_item()
+	 */
+	public $default = array(
+		// The $menu_item_data for wp_update_nav_menu_item().
+		'object_id'        => 0,
+		'object'           => '', // Taxonomy name.
+		'menu_item_parent' => 0, // A.K.A. menu-item-parent-id; note that post_parent is different, and not included.
+		'position'         => 0, // A.K.A. menu_order.
+		'type'             => 'custom', // Note that type_label is not included here.
+		'title'            => '',
+		'url'              => '',
+		'target'           => '',
+		'attr_title'       => '',
+		'description'      => '',
+		'classes'          => '',
+		'xfn'              => '',
+		'status'           => 'publish',
+		'original_title'   => '',
+		'nav_menu_term_id' => 0, // This will be supplied as the $menu_id arg for wp_update_nav_menu_item().
+		'_invalid'         => false,
+	);
+
+	/**
+	 * Default transport.
+	 *
+	 * @since 4.3.0
+	 * @since 4.5.0 Default changed to 'refresh'
+	 * @var string
+	 */
+	public $transport = 'refresh';
+
+	/**
+	 * The post ID represented by this setting instance. This is the db_id.
+	 *
+	 * A negative value represents a placeholder ID for a new menu not yet saved.
+	 *
+	 * @since 4.3.0
+	 * @var int
+	 */
+	public $post_id;
+
+	/**
+	 * Storage of pre-setup menu item to prevent wasted calls to wp_setup_nav_menu_item().
+	 *
+	 * @since 4.3.0
+	 * @var array|null
+	 */
+	protected $value;
+
+	/**
+	 * Previous (placeholder) post ID used before creating a new menu item.
+	 *
+	 * This value will be exported to JS via the customize_save_response filter
+	 * so that JavaScript can update the settings to refer to the newly-assigned
+	 * post ID. This value is always negative to indicate it does not refer to
+	 * a real post.
+	 *
+	 * @since 4.3.0
+	 * @var int
+	 *
+	 * @see WP_Customize_Nav_Menu_Item_Setting::update()
+	 * @see WP_Customize_Nav_Menu_Item_Setting::amend_customize_save_response()
+	 */
+	public $previous_post_id;
+
+	/**
+	 * When previewing or updating a menu item, this stores the previous nav_menu_term_id
+	 * which ensures that we can apply the proper filters.
+	 *
+	 * @since 4.3.0
+	 * @var int
+	 */
+	public $original_nav_menu_term_id;
+
+	/**
+	 * Whether or not update() was called.
+	 *
+	 * @since 4.3.0
+	 * @var bool
+	 */
+	protected $is_updated = false;
+
+	/**
+	 * Status for calling the update method, used in customize_save_response filter.
+	 *
+	 * See {@see 'customize_save_response'}.
+	 *
+	 * When status is inserted, the placeholder post ID is stored in $previous_post_id.
+	 * When status is error, the error is stored in $update_error.
+	 *
+	 * @since 4.3.0
+	 * @var string updated|inserted|deleted|error
+	 *
+	 * @see WP_Customize_Nav_Menu_Item_Setting::update()
+	 * @see WP_Customize_Nav_Menu_Item_Setting::amend_customize_save_response()
+	 */
+	public $update_status;
+
+	/**
+	 * Any error object returned by wp_update_nav_menu_item() when setting is updated.
+	 *
+	 * @since 4.3.0
+	 * @var WP_Error
+	 *
+	 * @see WP_Customize_Nav_Menu_Item_Setting::update()
+	 * @see WP_Customize_Nav_Menu_Item_Setting::amend_customize_save_response()
+	 */
+	public $update_error;
+
+	/**
+	 * Constructor.
+	 *
+	 * Any supplied $args override class property defaults.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @throws Exception If $id is not valid for this setting type.
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      A specific ID of the setting.
+	 *                                      Can be a theme mod or option name.
+	 * @param array                $args    Optional. Setting arguments.
+	 */
+	public function __construct( WP_Customize_Manager $manager, $id, array $args = array() ) {
+		if ( empty( $manager->nav_menus ) ) {
+			throw new Exception( 'Expected WP_Customize_Manager::$nav_menus to be set.' );
+		}
+
+		if ( ! preg_match( self::ID_PATTERN, $id, $matches ) ) {
+			throw new Exception( "Illegal widget setting ID: $id" );
+		}
+
+		$this->post_id = (int) $matches['id'];
+		add_action( 'wp_update_nav_menu_item', array( $this, 'flush_cached_value' ), 10, 2 );
+
+		parent::__construct( $manager, $id, $args );
+
+		// Ensure that an initially-supplied value is valid.
+		if ( isset( $this->value ) ) {
+			$this->populate_value();
+			foreach ( array_diff( array_keys( $this->default ), array_keys( $this->value ) ) as $missing ) {
+				throw new Exception( "Supplied nav_menu_item value missing property: $missing" );
+			}
+		}
+	}
+
+	/**
+	 * Clear the cached value when this nav menu item is updated.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @param int $menu_id       The term ID for the menu.
+	 * @param int $menu_item_id  The post ID for the menu item.
+	 */
+	public function flush_cached_value( $menu_id, $menu_item_id ) {
+		unset( $menu_id );
+		if ( $menu_item_id === $this->post_id ) {
+			$this->value = null;
+		}
+	}
+
+	/**
+	 * Get the instance data for a given nav_menu_item setting.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see wp_setup_nav_menu_item()
+	 *
+	 * @return array|false Instance data array, or false if the item is marked for deletion.
+	 */
+	public function value() {
+		if ( $this->is_previewed && get_current_blog_id() === $this->_previewed_blog_id ) {
+			$undefined  = new stdClass(); // Symbol.
+			$post_value = $this->post_value( $undefined );
+
+			if ( $undefined === $post_value ) {
+				$value = $this->_original_value;
+			} else {
+				$value = $post_value;
+			}
+			if ( ! empty( $value ) && empty( $value['original_title'] ) ) {
+				$value['original_title'] = $this->get_original_title( (object) $value );
+			}
+		} elseif ( isset( $this->value ) ) {
+			$value = $this->value;
+		} else {
+			$value = false;
+
+			// Note that an ID of less than one indicates a nav_menu not yet inserted.
+			if ( $this->post_id > 0 ) {
+				$post = get_post( $this->post_id );
+				if ( $post && self::POST_TYPE === $post->post_type ) {
+					$is_title_empty = empty( $post->post_title );
+					$value          = (array) wp_setup_nav_menu_item( $post );
+					if ( $is_title_empty ) {
+						$value['title'] = '';
+					}
+				}
+			}
+
+			if ( ! is_array( $value ) ) {
+				$value = $this->default;
+			}
+
+			// Cache the value for future calls to avoid having to re-call wp_setup_nav_menu_item().
+			$this->value = $value;
+			$this->populate_value();
+			$value = $this->value;
+		}
+
+		if ( ! empty( $value ) && empty( $value['type_label'] ) ) {
+			$value['type_label'] = $this->get_type_label( (object) $value );
+		}
+
+		return $value;
+	}
+
+	/**
+	 * Get original title.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @param object $item Nav menu item.
+	 * @return string The original title.
+	 */
+	protected function get_original_title( $item ) {
+		$original_title = '';
+		if ( 'post_type' === $item->type && ! empty( $item->object_id ) ) {
+			$original_object = get_post( $item->object_id );
+			if ( $original_object ) {
+				/** This filter is documented in wp-includes/post-template.php */
+				$original_title = apply_filters( 'the_title', $original_object->post_title, $original_object->ID );
+
+				if ( '' === $original_title ) {
+					/* translators: %d: ID of a post. */
+					$original_title = sprintf( __( '#%d (no title)' ), $original_object->ID );
+				}
+			}
+		} elseif ( 'taxonomy' === $item->type && ! empty( $item->object_id ) ) {
+			$original_term_title = get_term_field( 'name', $item->object_id, $item->object, 'raw' );
+			if ( ! is_wp_error( $original_term_title ) ) {
+				$original_title = $original_term_title;
+			}
+		} elseif ( 'post_type_archive' === $item->type ) {
+			$original_object = get_post_type_object( $item->object );
+			if ( $original_object ) {
+				$original_title = $original_object->labels->archives;
+			}
+		}
+		$original_title = html_entity_decode( $original_title, ENT_QUOTES, get_bloginfo( 'charset' ) );
+		return $original_title;
+	}
+
+	/**
+	 * Get type label.
+	 *
+	 * @since 4.7.0
+	 *
+	 * @param object $item Nav menu item.
+	 * @return string The type label.
+	 */
+	protected function get_type_label( $item ) {
+		if ( 'post_type' === $item->type ) {
+			$object = get_post_type_object( $item->object );
+			if ( $object ) {
+				$type_label = $object->labels->singular_name;
+			} else {
+				$type_label = $item->object;
+			}
+		} elseif ( 'taxonomy' === $item->type ) {
+			$object = get_taxonomy( $item->object );
+			if ( $object ) {
+				$type_label = $object->labels->singular_name;
+			} else {
+				$type_label = $item->object;
+			}
+		} elseif ( 'post_type_archive' === $item->type ) {
+			$type_label = __( 'Post Type Archive' );
+		} else {
+			$type_label = __( 'Custom Link' );
+		}
+		return $type_label;
+	}
+
+	/**
+	 * Ensure that the value is fully populated with the necessary properties.
+	 *
+	 * Translates some properties added by wp_setup_nav_menu_item() and removes others.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Nav_Menu_Item_Setting::value()
+	 */
+	protected function populate_value() {
+		if ( ! is_array( $this->value ) ) {
+			return;
+		}
+
+		if ( isset( $this->value['menu_order'] ) ) {
+			$this->value['position'] = $this->value['menu_order'];
+			unset( $this->value['menu_order'] );
+		}
+		if ( isset( $this->value['post_status'] ) ) {
+			$this->value['status'] = $this->value['post_status'];
+			unset( $this->value['post_status'] );
+		}
+
+		if ( ! isset( $this->value['original_title'] ) ) {
+			$this->value['original_title'] = $this->get_original_title( (object) $this->value );
+		}
+
+		if ( ! isset( $this->value['nav_menu_term_id'] ) && $this->post_id > 0 ) {
+			$menus = wp_get_post_terms(
+				$this->post_id,
+				WP_Customize_Nav_Menu_Setting::TAXONOMY,
+				array(
+					'fields' => 'ids',
+				)
+			);
+			if ( ! empty( $menus ) ) {
+				$this->value['nav_menu_term_id'] = array_shift( $menus );
+			} else {
+				$this->value['nav_menu_term_id'] = 0;
+			}
+		}
+
+		foreach ( array( 'object_id', 'menu_item_parent', 'nav_menu_term_id' ) as $key ) {
+			if ( ! is_int( $this->value[ $key ] ) ) {
+				$this->value[ $key ] = (int) $this->value[ $key ];
+			}
+		}
+		foreach ( array( 'classes', 'xfn' ) as $key ) {
+			if ( is_array( $this->value[ $key ] ) ) {
+				$this->value[ $key ] = implode( ' ', $this->value[ $key ] );
+			}
+		}
+
+		if ( ! isset( $this->value['title'] ) ) {
+			$this->value['title'] = '';
+		}
+
+		if ( ! isset( $this->value['_invalid'] ) ) {
+			$this->value['_invalid'] = false;
+			$is_known_invalid        = (
+				( ( 'post_type' === $this->value['type'] || 'post_type_archive' === $this->value['type'] ) && ! post_type_exists( $this->value['object'] ) )
+				||
+				( 'taxonomy' === $this->value['type'] && ! taxonomy_exists( $this->value['object'] ) )
+			);
+			if ( $is_known_invalid ) {
+				$this->value['_invalid'] = true;
+			}
+		}
+
+		// Remove remaining properties available on a setup nav_menu_item post object which aren't relevant to the setting value.
+		$irrelevant_properties = array(
+			'ID',
+			'comment_count',
+			'comment_status',
+			'db_id',
+			'filter',
+			'guid',
+			'ping_status',
+			'pinged',
+			'post_author',
+			'post_content',
+			'post_content_filtered',
+			'post_date',
+			'post_date_gmt',
+			'post_excerpt',
+			'post_mime_type',
+			'post_modified',
+			'post_modified_gmt',
+			'post_name',
+			'post_parent',
+			'post_password',
+			'post_title',
+			'post_type',
+			'to_ping',
+		);
+		foreach ( $irrelevant_properties as $property ) {
+			unset( $this->value[ $property ] );
+		}
+	}
+
+	/**
+	 * Handle previewing the setting.
+	 *
+	 * @since 4.3.0
+	 * @since 4.4.0 Added boolean return value.
+	 *
+	 * @see WP_Customize_Manager::post_value()
+	 *
+	 * @return bool False if method short-circuited due to no-op.
+	 */
+	public function preview() {
+		if ( $this->is_previewed ) {
+			return false;
+		}
+
+		$undefined      = new stdClass();
+		$is_placeholder = ( $this->post_id < 0 );
+		$is_dirty       = ( $undefined !== $this->post_value( $undefined ) );
+		if ( ! $is_placeholder && ! $is_dirty ) {
+			return false;
+		}
+
+		$this->is_previewed              = true;
+		$this->_original_value           = $this->value();
+		$this->original_nav_menu_term_id = $this->_original_value['nav_menu_term_id'];
+		$this->_previewed_blog_id        = get_current_blog_id();
+
+		add_filter( 'wp_get_nav_menu_items', array( $this, 'filter_wp_get_nav_menu_items' ), 10, 3 );
+
+		$sort_callback = array( __CLASS__, 'sort_wp_get_nav_menu_items' );
+		if ( ! has_filter( 'wp_get_nav_menu_items', $sort_callback ) ) {
+			add_filter( 'wp_get_nav_menu_items', array( __CLASS__, 'sort_wp_get_nav_menu_items' ), 1000, 3 );
+		}
+
+		// @todo Add get_post_metadata filters for plugins to add their data.
+
+		return true;
+	}
+
+	/**
+	 * Filters the wp_get_nav_menu_items() result to supply the previewed menu items.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see wp_get_nav_menu_items()
+	 *
+	 * @param WP_Post[] $items An array of menu item post objects.
+	 * @param WP_Term   $menu  The menu object.
+	 * @param array     $args  An array of arguments used to retrieve menu item objects.
+	 * @return WP_Post[] Array of menu item objects.
+	 */
+	public function filter_wp_get_nav_menu_items( $items, $menu, $args ) {
+		$this_item                = $this->value();
+		$current_nav_menu_term_id = null;
+		if ( isset( $this_item['nav_menu_term_id'] ) ) {
+			$current_nav_menu_term_id = $this_item['nav_menu_term_id'];
+			unset( $this_item['nav_menu_term_id'] );
+		}
+
+		$should_filter = (
+			$menu->term_id === $this->original_nav_menu_term_id
+			||
+			$menu->term_id === $current_nav_menu_term_id
+		);
+		if ( ! $should_filter ) {
+			return $items;
+		}
+
+		// Handle deleted menu item, or menu item moved to another menu.
+		$should_remove = (
+			false === $this_item
+			||
+			( isset( $this_item['_invalid'] ) && true === $this_item['_invalid'] )
+			||
+			(
+				$this->original_nav_menu_term_id === $menu->term_id
+				&&
+				$current_nav_menu_term_id !== $this->original_nav_menu_term_id
+			)
+		);
+		if ( $should_remove ) {
+			$filtered_items = array();
+			foreach ( $items as $item ) {
+				if ( $item->db_id !== $this->post_id ) {
+					$filtered_items[] = $item;
+				}
+			}
+			return $filtered_items;
+		}
+
+		$mutated       = false;
+		$should_update = (
+			is_array( $this_item )
+			&&
+			$current_nav_menu_term_id === $menu->term_id
+		);
+		if ( $should_update ) {
+			foreach ( $items as $item ) {
+				if ( $item->db_id === $this->post_id ) {
+					foreach ( get_object_vars( $this->value_as_wp_post_nav_menu_item() ) as $key => $value ) {
+						$item->$key = $value;
+					}
+					$mutated = true;
+				}
+			}
+
+			// Not found so we have to append it..
+			if ( ! $mutated ) {
+				$items[] = $this->value_as_wp_post_nav_menu_item();
+			}
+		}
+
+		return $items;
+	}
+
+	/**
+	 * Re-apply the tail logic also applied on $items by wp_get_nav_menu_items().
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see wp_get_nav_menu_items()
+	 *
+	 * @param WP_Post[] $items An array of menu item post objects.
+	 * @param WP_Term   $menu  The menu object.
+	 * @param array     $args  An array of arguments used to retrieve menu item objects.
+	 * @return WP_Post[] Array of menu item objects.
+	 */
+	public static function sort_wp_get_nav_menu_items( $items, $menu, $args ) {
+		// @todo We should probably re-apply some constraints imposed by $args.
+		unset( $args['include'] );
+
+		// Remove invalid items only in front end.
+		if ( ! is_admin() ) {
+			$items = array_filter( $items, '_is_valid_nav_menu_item' );
+		}
+
+		if ( ARRAY_A === $args['output'] ) {
+			$items = wp_list_sort(
+				$items,
+				array(
+					$args['output_key'] => 'ASC',
+				)
+			);
+			$i     = 1;
+
+			foreach ( $items as $k => $item ) {
+				$items[ $k ]->{$args['output_key']} = $i++;
+			}
+		}
+
+		return $items;
+	}
+
+	/**
+	 * Get the value emulated into a WP_Post and set up as a nav_menu_item.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @return WP_Post With wp_setup_nav_menu_item() applied.
+	 */
+	public function value_as_wp_post_nav_menu_item() {
+		$item = (object) $this->value();
+		unset( $item->nav_menu_term_id );
+
+		$item->post_status = $item->status;
+		unset( $item->status );
+
+		$item->post_type  = 'nav_menu_item';
+		$item->menu_order = $item->position;
+		unset( $item->position );
+
+		if ( empty( $item->original_title ) ) {
+			$item->original_title = $this->get_original_title( $item );
+		}
+		if ( empty( $item->title ) && ! empty( $item->original_title ) ) {
+			$item->title = $item->original_title;
+		}
+		if ( $item->title ) {
+			$item->post_title = $item->title;
+		}
+
+		// 'classes' should be an array, as in wp_setup_nav_menu_item().
+		if ( isset( $item->classes ) && is_scalar( $item->classes ) ) {
+			$item->classes = explode( ' ', $item->classes );
+		}
+
+		$item->ID    = $this->post_id;
+		$item->db_id = $this->post_id;
+		$post        = new WP_Post( (object) $item );
+
+		if ( empty( $post->post_author ) ) {
+			$post->post_author = get_current_user_id();
+		}
+
+		if ( ! isset( $post->type_label ) ) {
+			$post->type_label = $this->get_type_label( $post );
+		}
+
+		// Ensure nav menu item URL is set according to linked object.
+		if ( 'post_type' === $post->type && ! empty( $post->object_id ) ) {
+			$post->url = get_permalink( $post->object_id );
+		} elseif ( 'taxonomy' === $post->type && ! empty( $post->object ) && ! empty( $post->object_id ) ) {
+			$post->url = get_term_link( (int) $post->object_id, $post->object );
+		} elseif ( 'post_type_archive' === $post->type && ! empty( $post->object ) ) {
+			$post->url = get_post_type_archive_link( $post->object );
+		}
+		if ( is_wp_error( $post->url ) ) {
+			$post->url = '';
+		}
+
+		/** This filter is documented in wp-includes/nav-menu.php */
+		$post->attr_title = apply_filters( 'nav_menu_attr_title', $post->attr_title );
+
+		/** This filter is documented in wp-includes/nav-menu.php */
+		$post->description = apply_filters( 'nav_menu_description', wp_trim_words( $post->description, 200 ) );
+
+		/** This filter is documented in wp-includes/nav-menu.php */
+		$post = apply_filters( 'wp_setup_nav_menu_item', $post );
+
+		return $post;
+	}
+
+	/**
+	 * Sanitize an input.
+	 *
+	 * Note that parent::sanitize() erroneously does wp_unslash() on $value, but
+	 * we remove that in this override.
+	 *
+	 * @since 4.3.0
+	 * @since 5.9.0 Renamed `$menu_item_value` to `$value` for PHP 8 named parameter support.
+	 *
+	 * @param array $value The menu item value to sanitize.
+	 * @return array|false|null|WP_Error Null or WP_Error if an input isn't valid. False if it is marked for deletion.
+	 *                                   Otherwise the sanitized value.
+	 */
+	public function sanitize( $value ) {
+		// Restores the more descriptive, specific name for use within this method.
+		$menu_item_value = $value;
+
+		// Menu is marked for deletion.
+		if ( false === $menu_item_value ) {
+			return $menu_item_value;
+		}
+
+		// Invalid.
+		if ( ! is_array( $menu_item_value ) ) {
+			return null;
+		}
+
+		$default                     = array(
+			'object_id'        => 0,
+			'object'           => '',
+			'menu_item_parent' => 0,
+			'position'         => 0,
+			'type'             => 'custom',
+			'title'            => '',
+			'url'              => '',
+			'target'           => '',
+			'attr_title'       => '',
+			'description'      => '',
+			'classes'          => '',
+			'xfn'              => '',
+			'status'           => 'publish',
+			'original_title'   => '',
+			'nav_menu_term_id' => 0,
+			'_invalid'         => false,
+		);
+		$menu_item_value             = array_merge( $default, $menu_item_value );
+		$menu_item_value             = wp_array_slice_assoc( $menu_item_value, array_keys( $default ) );
+		$menu_item_value['position'] = (int) $menu_item_value['position'];
+
+		foreach ( array( 'object_id', 'menu_item_parent', 'nav_menu_term_id' ) as $key ) {
+			// Note we need to allow negative-integer IDs for previewed objects not inserted yet.
+			$menu_item_value[ $key ] = (int) $menu_item_value[ $key ];
+		}
+
+		foreach ( array( 'type', 'object', 'target' ) as $key ) {
+			$menu_item_value[ $key ] = sanitize_key( $menu_item_value[ $key ] );
+		}
+
+		foreach ( array( 'xfn', 'classes' ) as $key ) {
+			$value = $menu_item_value[ $key ];
+			if ( ! is_array( $value ) ) {
+				$value = explode( ' ', $value );
+			}
+			$menu_item_value[ $key ] = implode( ' ', array_map( 'sanitize_html_class', $value ) );
+		}
+
+		$menu_item_value['original_title'] = sanitize_text_field( $menu_item_value['original_title'] );
+
+		// Apply the same filters as when calling wp_insert_post().
+
+		/** This filter is documented in wp-includes/post.php */
+		$menu_item_value['title'] = wp_unslash( apply_filters( 'title_save_pre', wp_slash( $menu_item_value['title'] ) ) );
+
+		/** This filter is documented in wp-includes/post.php */
+		$menu_item_value['attr_title'] = wp_unslash( apply_filters( 'excerpt_save_pre', wp_slash( $menu_item_value['attr_title'] ) ) );
+
+		/** This filter is documented in wp-includes/post.php */
+		$menu_item_value['description'] = wp_unslash( apply_filters( 'content_save_pre', wp_slash( $menu_item_value['description'] ) ) );
+
+		if ( '' !== $menu_item_value['url'] ) {
+			$menu_item_value['url'] = sanitize_url( $menu_item_value['url'] );
+			if ( '' === $menu_item_value['url'] ) {
+				return new WP_Error( 'invalid_url', __( 'Invalid URL.' ) ); // Fail sanitization if URL is invalid.
+			}
+		}
+		if ( 'publish' !== $menu_item_value['status'] ) {
+			$menu_item_value['status'] = 'draft';
+		}
+
+		$menu_item_value['_invalid'] = (bool) $menu_item_value['_invalid'];
+
+		/** This filter is documented in wp-includes/class-wp-customize-setting.php */
+		return apply_filters( "customize_sanitize_{$this->id}", $menu_item_value, $this );
+	}
+
+	/**
+	 * Creates/updates the nav_menu_item post for this setting.
+	 *
+	 * Any created menu items will have their assigned post IDs exported to the client
+	 * via the {@see 'customize_save_response'} filter. Likewise, any errors will be
+	 * exported to the client via the customize_save_response() filter.
+	 *
+	 * To delete a menu, the client can send false as the value.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see wp_update_nav_menu_item()
+	 *
+	 * @param array|false $value The menu item array to update. If false, then the menu item will be deleted
+	 *                           entirely. See WP_Customize_Nav_Menu_Item_Setting::$default for what the value
+	 *                           should consist of.
+	 * @return null|void
+	 */
+	protected function update( $value ) {
+		if ( $this->is_updated ) {
+			return;
+		}
+
+		$this->is_updated = true;
+		$is_placeholder   = ( $this->post_id < 0 );
+		$is_delete        = ( false === $value );
+
+		// Update the cached value.
+		$this->value = $value;
+
+		add_filter( 'customize_save_response', array( $this, 'amend_customize_save_response' ) );
+
+		if ( $is_delete ) {
+			// If the current setting post is a placeholder, a delete request is a no-op.
+			if ( $is_placeholder ) {
+				$this->update_status = 'deleted';
+			} else {
+				$r = wp_delete_post( $this->post_id, true );
+
+				if ( false === $r ) {
+					$this->update_error  = new WP_Error( 'delete_failure' );
+					$this->update_status = 'error';
+				} else {
+					$this->update_status = 'deleted';
+				}
+				// @todo send back the IDs for all associated nav menu items deleted, so these settings (and controls) can be removed from Customizer?
+			}
+		} else {
+
+			// Handle saving menu items for menus that are being newly-created.
+			if ( $value['nav_menu_term_id'] < 0 ) {
+				$nav_menu_setting_id = sprintf( 'nav_menu[%s]', $value['nav_menu_term_id'] );
+				$nav_menu_setting    = $this->manager->get_setting( $nav_menu_setting_id );
+
+				if ( ! $nav_menu_setting || ! ( $nav_menu_setting instanceof WP_Customize_Nav_Menu_Setting ) ) {
+					$this->update_status = 'error';
+					$this->update_error  = new WP_Error( 'unexpected_nav_menu_setting' );
+					return;
+				}
+
+				if ( false === $nav_menu_setting->save() ) {
+					$this->update_status = 'error';
+					$this->update_error  = new WP_Error( 'nav_menu_setting_failure' );
+					return;
+				}
+
+				if ( (int) $value['nav_menu_term_id'] !== $nav_menu_setting->previous_term_id ) {
+					$this->update_status = 'error';
+					$this->update_error  = new WP_Error( 'unexpected_previous_term_id' );
+					return;
+				}
+
+				$value['nav_menu_term_id'] = $nav_menu_setting->term_id;
+			}
+
+			// Handle saving a nav menu item that is a child of a nav menu item being newly-created.
+			if ( $value['menu_item_parent'] < 0 ) {
+				$parent_nav_menu_item_setting_id = sprintf( 'nav_menu_item[%s]', $value['menu_item_parent'] );
+				$parent_nav_menu_item_setting    = $this->manager->get_setting( $parent_nav_menu_item_setting_id );
+
+				if ( ! $parent_nav_menu_item_setting || ! ( $parent_nav_menu_item_setting instanceof WP_Customize_Nav_Menu_Item_Setting ) ) {
+					$this->update_status = 'error';
+					$this->update_error  = new WP_Error( 'unexpected_nav_menu_item_setting' );
+					return;
+				}
+
+				if ( false === $parent_nav_menu_item_setting->save() ) {
+					$this->update_status = 'error';
+					$this->update_error  = new WP_Error( 'nav_menu_item_setting_failure' );
+					return;
+				}
+
+				if ( (int) $value['menu_item_parent'] !== $parent_nav_menu_item_setting->previous_post_id ) {
+					$this->update_status = 'error';
+					$this->update_error  = new WP_Error( 'unexpected_previous_post_id' );
+					return;
+				}
+
+				$value['menu_item_parent'] = $parent_nav_menu_item_setting->post_id;
+			}
+
+			// Insert or update menu.
+			$menu_item_data = array(
+				'menu-item-object-id'   => $value['object_id'],
+				'menu-item-object'      => $value['object'],
+				'menu-item-parent-id'   => $value['menu_item_parent'],
+				'menu-item-position'    => $value['position'],
+				'menu-item-type'        => $value['type'],
+				'menu-item-title'       => $value['title'],
+				'menu-item-url'         => $value['url'],
+				'menu-item-description' => $value['description'],
+				'menu-item-attr-title'  => $value['attr_title'],
+				'menu-item-target'      => $value['target'],
+				'menu-item-classes'     => $value['classes'],
+				'menu-item-xfn'         => $value['xfn'],
+				'menu-item-status'      => $value['status'],
+			);
+
+			$r = wp_update_nav_menu_item(
+				$value['nav_menu_term_id'],
+				$is_placeholder ? 0 : $this->post_id,
+				wp_slash( $menu_item_data )
+			);
+
+			if ( is_wp_error( $r ) ) {
+				$this->update_status = 'error';
+				$this->update_error  = $r;
+			} else {
+				if ( $is_placeholder ) {
+					$this->previous_post_id = $this->post_id;
+					$this->post_id          = $r;
+					$this->update_status    = 'inserted';
+				} else {
+					$this->update_status = 'updated';
+				}
+			}
+		}
+	}
+
+	/**
+	 * Export data for the JS client.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Nav_Menu_Item_Setting::update()
+	 *
+	 * @param array $data Additional information passed back to the 'saved' event on `wp.customize`.
+	 * @return array Save response data.
+	 */
+	public function amend_customize_save_response( $data ) {
+		if ( ! isset( $data['nav_menu_item_updates'] ) ) {
+			$data['nav_menu_item_updates'] = array();
+		}
+
+		$data['nav_menu_item_updates'][] = array(
+			'post_id'          => $this->post_id,
+			'previous_post_id' => $this->previous_post_id,
+			'error'            => $this->update_error ? $this->update_error->get_error_code() : null,
+			'status'           => $this->update_status,
+		);
+		return $data;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-location-control.php b/wp-includes/customize/class-wp-customize-nav-menu-location-control.php
new file mode 100644
index 0000000..4877ada
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-location-control.php
@@ -0,0 +1,89 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Location_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Menu Location Control Class.
+ *
+ * This custom control is only needed for JS.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Nav_Menu_Location_Control extends WP_Customize_Control {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'nav_menu_location';
+
+	/**
+	 * Location ID.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $location_id = '';
+
+	/**
+	 * Refresh the parameters passed to JavaScript via JSON.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Control::to_json()
+	 */
+	public function to_json() {
+		parent::to_json();
+		$this->json['locationId'] = $this->location_id;
+	}
+
+	/**
+	 * Render content just like a normal select control.
+	 *
+	 * @since 4.3.0
+	 * @since 4.9.0 Added a button to create menus.
+	 */
+	public function render_content() {
+		if ( empty( $this->choices ) ) {
+			return;
+		}
+
+		$value_hidden_class    = '';
+		$no_value_hidden_class = '';
+		if ( $this->value() ) {
+			$value_hidden_class = ' hidden';
+		} else {
+			$no_value_hidden_class = ' hidden';
+		}
+		?>
+		<label>
+			<?php if ( ! empty( $this->label ) ) : ?>
+			<span class="customize-control-title"><?php echo esc_html( $this->label ); ?></span>
+			<?php endif; ?>
+
+			<?php if ( ! empty( $this->description ) ) : ?>
+			<span class="description customize-control-description"><?php echo $this->description; ?></span>
+			<?php endif; ?>
+
+			<select <?php $this->link(); ?>>
+				<?php
+				foreach ( $this->choices as $value => $label ) :
+					echo '<option value="' . esc_attr( $value ) . '"' . selected( $this->value(), $value, false ) . '>' . $label . '</option>';
+				endforeach;
+				?>
+			</select>
+		</label>
+		<button type="button" class="button-link create-menu<?php echo $value_hidden_class; ?>" data-location-id="<?php echo esc_attr( $this->location_id ); ?>" aria-label="<?php esc_attr_e( 'Create a menu for this location' ); ?>"><?php _e( '+ Create New Menu' ); ?></button>
+		<button type="button" class="button-link edit-menu<?php echo $no_value_hidden_class; ?>" aria-label="<?php esc_attr_e( 'Edit selected menu' ); ?>"><?php _e( 'Edit Menu' ); ?></button>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-locations-control.php b/wp-includes/customize/class-wp-customize-nav-menu-locations-control.php
new file mode 100644
index 0000000..434fcba
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-locations-control.php
@@ -0,0 +1,92 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Locations_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.9.0
+ */
+
+/**
+ * Customize Nav Menu Locations Control Class.
+ *
+ * @since 4.9.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Nav_Menu_Locations_Control extends WP_Customize_Control {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.9.0
+	 * @var string
+	 */
+	public $type = 'nav_menu_locations';
+
+	/**
+	 * Don't render the control's content - it uses a JS template instead.
+	 *
+	 * @since 4.9.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * JS/Underscore template for the control UI.
+	 *
+	 * @since 4.9.0
+	 */
+	public function content_template() {
+		if ( current_theme_supports( 'menus' ) ) :
+			?>
+			<# var elementId; #>
+			<ul class="menu-location-settings">
+				<li class="customize-control assigned-menu-locations-title">
+					<span class="customize-control-title">{{ wp.customize.Menus.data.l10n.locationsTitle }}</span>
+					<# if ( data.isCreating ) { #>
+						<p>
+							<?php echo _x( 'Where do you want this menu to appear?', 'menu locations' ); ?>
+							<?php
+							printf(
+								/* translators: 1: Documentation URL, 2: Additional link attributes, 3: Accessibility text. */
+								_x( '(If you plan to use a menu <a href="%1$s" %2$s>widget%3$s</a>, skip this step.)', 'menu locations' ),
+								__( 'https://wordpress.org/documentation/article/manage-wordpress-widgets/' ),
+								' class="external-link" target="_blank"',
+								sprintf(
+									'<span class="screen-reader-text"> %s</span>',
+									/* translators: Hidden accessibility text. */
+									__( '(opens in a new tab)' )
+								)
+							);
+							?>
+						</p>
+					<# } else { #>
+						<p><?php echo _x( 'Here&#8217;s where this menu appears. If you would like to change that, pick another location.', 'menu locations' ); ?></p>
+					<# } #>
+				</li>
+
+				<?php foreach ( get_registered_nav_menus() as $location => $description ) : ?>
+					<# elementId = _.uniqueId( 'customize-nav-menu-control-location-' ); #>
+					<li class="customize-control customize-control-checkbox assigned-menu-location">
+						<span class="customize-inside-control-row">
+							<input id="{{ elementId }}" type="checkbox" data-menu-id="{{ data.menu_id }}" data-location-id="<?php echo esc_attr( $location ); ?>" class="menu-location" />
+							<label for="{{ elementId }}">
+								<?php echo $description; ?>
+								<span class="theme-location-set">
+									<?php
+									printf(
+										/* translators: %s: Menu name. */
+										_x( '(Current: %s)', 'menu location' ),
+										'<span class="current-menu-location-name-' . esc_attr( $location ) . '"></span>'
+									);
+									?>
+								</span>
+							</label>
+						</span>
+					</li>
+				<?php endforeach; ?>
+			</ul>
+			<?php
+		endif;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-name-control.php b/wp-includes/customize/class-wp-customize-nav-menu-name-control.php
new file mode 100644
index 0000000..221c4a9
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-name-control.php
@@ -0,0 +1,56 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Name_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize control to represent the name field for a given menu.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Nav_Menu_Name_Control extends WP_Customize_Control {
+
+	/**
+	 * Type of control, used by JS.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'nav_menu_name';
+
+	/**
+	 * No-op since we're using JS template.
+	 *
+	 * @since 4.3.0
+	 */
+	protected function render_content() {}
+
+	/**
+	 * Render the Underscore template for this control.
+	 *
+	 * @since 4.3.0
+	 */
+	protected function content_template() {
+		?>
+		<label>
+			<# if ( data.label ) { #>
+				<span class="customize-control-title">{{ data.label }}</span>
+			<# } #>
+			<input type="text" class="menu-name-field live-update-section-title"
+				<# if ( data.description ) { #>
+					aria-describedby="{{ data.section }}-description"
+				<# } #>
+				/>
+		</label>
+		<# if ( data.description ) { #>
+			<p id="{{ data.section }}-description">{{ data.description }}</p>
+		<# } #>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-section.php b/wp-includes/customize/class-wp-customize-nav-menu-section.php
new file mode 100644
index 0000000..225d035
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-section.php
@@ -0,0 +1,41 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Section class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Menu Section Class
+ *
+ * Custom section only needed in JS.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Section
+ */
+class WP_Customize_Nav_Menu_Section extends WP_Customize_Section {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'nav_menu';
+
+	/**
+	 * Get section parameters for JS.
+	 *
+	 * @since 4.3.0
+	 * @return array Exported parameters.
+	 */
+	public function json() {
+		$exported            = parent::json();
+		$exported['menu_id'] = (int) preg_replace( '/^nav_menu\[(-?\d+)\]/', '$1', $this->id );
+
+		return $exported;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menu-setting.php b/wp-includes/customize/class-wp-customize-nav-menu-setting.php
new file mode 100644
index 0000000..f01906c
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menu-setting.php
@@ -0,0 +1,651 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menu_Setting class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Setting to represent a nav_menu.
+ *
+ * Subclass of WP_Customize_Setting to represent a nav_menu taxonomy term, and
+ * the IDs for the nav_menu_items associated with the nav menu.
+ *
+ * @since 4.3.0
+ *
+ * @see wp_get_nav_menu_object()
+ * @see WP_Customize_Setting
+ */
+class WP_Customize_Nav_Menu_Setting extends WP_Customize_Setting {
+
+	const ID_PATTERN = '/^nav_menu\[(?P<id>-?\d+)\]$/';
+
+	const TAXONOMY = 'nav_menu';
+
+	const TYPE = 'nav_menu';
+
+	/**
+	 * Setting type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = self::TYPE;
+
+	/**
+	 * Default setting value.
+	 *
+	 * @since 4.3.0
+	 * @var array
+	 *
+	 * @see wp_get_nav_menu_object()
+	 */
+	public $default = array(
+		'name'        => '',
+		'description' => '',
+		'parent'      => 0,
+		'auto_add'    => false,
+	);
+
+	/**
+	 * Default transport.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $transport = 'postMessage';
+
+	/**
+	 * The term ID represented by this setting instance.
+	 *
+	 * A negative value represents a placeholder ID for a new menu not yet saved.
+	 *
+	 * @since 4.3.0
+	 * @var int
+	 */
+	public $term_id;
+
+	/**
+	 * Previous (placeholder) term ID used before creating a new menu.
+	 *
+	 * This value will be exported to JS via the {@see 'customize_save_response'} filter
+	 * so that JavaScript can update the settings to refer to the newly-assigned
+	 * term ID. This value is always negative to indicate it does not refer to
+	 * a real term.
+	 *
+	 * @since 4.3.0
+	 * @var int
+	 *
+	 * @see WP_Customize_Nav_Menu_Setting::update()
+	 * @see WP_Customize_Nav_Menu_Setting::amend_customize_save_response()
+	 */
+	public $previous_term_id;
+
+	/**
+	 * Whether or not update() was called.
+	 *
+	 * @since 4.3.0
+	 * @var bool
+	 */
+	protected $is_updated = false;
+
+	/**
+	 * Status for calling the update method, used in customize_save_response filter.
+	 *
+	 * See {@see 'customize_save_response'}.
+	 *
+	 * When status is inserted, the placeholder term ID is stored in `$previous_term_id`.
+	 * When status is error, the error is stored in `$update_error`.
+	 *
+	 * @since 4.3.0
+	 * @var string updated|inserted|deleted|error
+	 *
+	 * @see WP_Customize_Nav_Menu_Setting::update()
+	 * @see WP_Customize_Nav_Menu_Setting::amend_customize_save_response()
+	 */
+	public $update_status;
+
+	/**
+	 * Any error object returned by wp_update_nav_menu_object() when setting is updated.
+	 *
+	 * @since 4.3.0
+	 * @var WP_Error
+	 *
+	 * @see WP_Customize_Nav_Menu_Setting::update()
+	 * @see WP_Customize_Nav_Menu_Setting::amend_customize_save_response()
+	 */
+	public $update_error;
+
+	/**
+	 * Constructor.
+	 *
+	 * Any supplied $args override class property defaults.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @throws Exception If $id is not valid for this setting type.
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      A specific ID of the setting.
+	 *                                      Can be a theme mod or option name.
+	 * @param array                $args    Optional. Setting arguments.
+	 */
+	public function __construct( WP_Customize_Manager $manager, $id, array $args = array() ) {
+		if ( empty( $manager->nav_menus ) ) {
+			throw new Exception( 'Expected WP_Customize_Manager::$nav_menus to be set.' );
+		}
+
+		if ( ! preg_match( self::ID_PATTERN, $id, $matches ) ) {
+			throw new Exception( "Illegal widget setting ID: $id" );
+		}
+
+		$this->term_id = (int) $matches['id'];
+
+		parent::__construct( $manager, $id, $args );
+	}
+
+	/**
+	 * Get the instance data for a given widget setting.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see wp_get_nav_menu_object()
+	 *
+	 * @return array Instance data.
+	 */
+	public function value() {
+		if ( $this->is_previewed && get_current_blog_id() === $this->_previewed_blog_id ) {
+			$undefined  = new stdClass(); // Symbol.
+			$post_value = $this->post_value( $undefined );
+
+			if ( $undefined === $post_value ) {
+				$value = $this->_original_value;
+			} else {
+				$value = $post_value;
+			}
+		} else {
+			$value = false;
+
+			// Note that a term_id of less than one indicates a nav_menu not yet inserted.
+			if ( $this->term_id > 0 ) {
+				$term = wp_get_nav_menu_object( $this->term_id );
+
+				if ( $term ) {
+					$value = wp_array_slice_assoc( (array) $term, array_keys( $this->default ) );
+
+					$nav_menu_options  = (array) get_option( 'nav_menu_options', array() );
+					$value['auto_add'] = false;
+
+					if ( isset( $nav_menu_options['auto_add'] ) && is_array( $nav_menu_options['auto_add'] ) ) {
+						$value['auto_add'] = in_array( $term->term_id, $nav_menu_options['auto_add'], true );
+					}
+				}
+			}
+
+			if ( ! is_array( $value ) ) {
+				$value = $this->default;
+			}
+		}
+
+		return $value;
+	}
+
+	/**
+	 * Handle previewing the setting.
+	 *
+	 * @since 4.3.0
+	 * @since 4.4.0 Added boolean return value
+	 *
+	 * @see WP_Customize_Manager::post_value()
+	 *
+	 * @return bool False if method short-circuited due to no-op.
+	 */
+	public function preview() {
+		if ( $this->is_previewed ) {
+			return false;
+		}
+
+		$undefined      = new stdClass();
+		$is_placeholder = ( $this->term_id < 0 );
+		$is_dirty       = ( $undefined !== $this->post_value( $undefined ) );
+		if ( ! $is_placeholder && ! $is_dirty ) {
+			return false;
+		}
+
+		$this->is_previewed       = true;
+		$this->_original_value    = $this->value();
+		$this->_previewed_blog_id = get_current_blog_id();
+
+		add_filter( 'wp_get_nav_menus', array( $this, 'filter_wp_get_nav_menus' ), 10, 2 );
+		add_filter( 'wp_get_nav_menu_object', array( $this, 'filter_wp_get_nav_menu_object' ), 10, 2 );
+		add_filter( 'default_option_nav_menu_options', array( $this, 'filter_nav_menu_options' ) );
+		add_filter( 'option_nav_menu_options', array( $this, 'filter_nav_menu_options' ) );
+
+		return true;
+	}
+
+	/**
+	 * Filters the wp_get_nav_menus() result to ensure the inserted menu object is included, and the deleted one is removed.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see wp_get_nav_menus()
+	 *
+	 * @param WP_Term[] $menus An array of menu objects.
+	 * @param array     $args  An array of arguments used to retrieve menu objects.
+	 * @return WP_Term[] Array of menu objects.
+	 */
+	public function filter_wp_get_nav_menus( $menus, $args ) {
+		if ( get_current_blog_id() !== $this->_previewed_blog_id ) {
+			return $menus;
+		}
+
+		$setting_value = $this->value();
+		$is_delete     = ( false === $setting_value );
+		$index         = -1;
+
+		// Find the existing menu item's position in the list.
+		foreach ( $menus as $i => $menu ) {
+			if ( (int) $this->term_id === (int) $menu->term_id || (int) $this->previous_term_id === (int) $menu->term_id ) {
+				$index = $i;
+				break;
+			}
+		}
+
+		if ( $is_delete ) {
+			// Handle deleted menu by removing it from the list.
+			if ( -1 !== $index ) {
+				array_splice( $menus, $index, 1 );
+			}
+		} else {
+			// Handle menus being updated or inserted.
+			$menu_obj = (object) array_merge(
+				array(
+					'term_id'          => $this->term_id,
+					'term_taxonomy_id' => $this->term_id,
+					'slug'             => sanitize_title( $setting_value['name'] ),
+					'count'            => 0,
+					'term_group'       => 0,
+					'taxonomy'         => self::TAXONOMY,
+					'filter'           => 'raw',
+				),
+				$setting_value
+			);
+
+			array_splice( $menus, $index, ( -1 === $index ? 0 : 1 ), array( $menu_obj ) );
+		}
+
+		// Make sure the menu objects get re-sorted after an update/insert.
+		if ( ! $is_delete && ! empty( $args['orderby'] ) ) {
+			$menus = wp_list_sort(
+				$menus,
+				array(
+					$args['orderby'] => 'ASC',
+				)
+			);
+		}
+		// @todo Add support for $args['hide_empty'] === true.
+
+		return $menus;
+	}
+
+	/**
+	 * Temporary non-closure passing of orderby value to function.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 *
+	 * @see WP_Customize_Nav_Menu_Setting::filter_wp_get_nav_menus()
+	 * @see WP_Customize_Nav_Menu_Setting::_sort_menus_by_orderby()
+	 */
+	protected $_current_menus_sort_orderby;
+
+	/**
+	 * Sort menu objects by the class-supplied orderby property.
+	 *
+	 * This is a workaround for a lack of closures.
+	 *
+	 * @since 4.3.0
+	 * @deprecated 4.7.0 Use wp_list_sort()
+	 *
+	 * @param object $menu1
+	 * @param object $menu2
+	 * @return int
+	 *
+	 * @see WP_Customize_Nav_Menu_Setting::filter_wp_get_nav_menus()
+	 */
+	protected function _sort_menus_by_orderby( $menu1, $menu2 ) {
+		_deprecated_function( __METHOD__, '4.7.0', 'wp_list_sort' );
+
+		$key = $this->_current_menus_sort_orderby;
+		return strcmp( $menu1->$key, $menu2->$key );
+	}
+
+	/**
+	 * Filters the wp_get_nav_menu_object() result to supply the previewed menu object.
+	 *
+	 * Requesting a nav_menu object by anything but ID is not supported.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see wp_get_nav_menu_object()
+	 *
+	 * @param object|null $menu_obj Object returned by wp_get_nav_menu_object().
+	 * @param string      $menu_id  ID of the nav_menu term. Requests by slug or name will be ignored.
+	 * @return object|null
+	 */
+	public function filter_wp_get_nav_menu_object( $menu_obj, $menu_id ) {
+		$ok = (
+			get_current_blog_id() === $this->_previewed_blog_id
+			&&
+			is_int( $menu_id )
+			&&
+			$menu_id === $this->term_id
+		);
+		if ( ! $ok ) {
+			return $menu_obj;
+		}
+
+		$setting_value = $this->value();
+
+		// Handle deleted menus.
+		if ( false === $setting_value ) {
+			return false;
+		}
+
+		// Handle sanitization failure by preventing short-circuiting.
+		if ( null === $setting_value ) {
+			return $menu_obj;
+		}
+
+		$menu_obj = (object) array_merge(
+			array(
+				'term_id'          => $this->term_id,
+				'term_taxonomy_id' => $this->term_id,
+				'slug'             => sanitize_title( $setting_value['name'] ),
+				'count'            => 0,
+				'term_group'       => 0,
+				'taxonomy'         => self::TAXONOMY,
+				'filter'           => 'raw',
+			),
+			$setting_value
+		);
+
+		return $menu_obj;
+	}
+
+	/**
+	 * Filters the nav_menu_options option to include this menu's auto_add preference.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @param array $nav_menu_options Nav menu options including auto_add.
+	 * @return array (Maybe) modified nav menu options.
+	 */
+	public function filter_nav_menu_options( $nav_menu_options ) {
+		if ( get_current_blog_id() !== $this->_previewed_blog_id ) {
+			return $nav_menu_options;
+		}
+
+		$menu             = $this->value();
+		$nav_menu_options = $this->filter_nav_menu_options_value(
+			$nav_menu_options,
+			$this->term_id,
+			false === $menu ? false : $menu['auto_add']
+		);
+
+		return $nav_menu_options;
+	}
+
+	/**
+	 * Sanitize an input.
+	 *
+	 * Note that parent::sanitize() erroneously does wp_unslash() on $value, but
+	 * we remove that in this override.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @param array $value The menu value to sanitize.
+	 * @return array|false|null Null if an input isn't valid. False if it is marked for deletion.
+	 *                          Otherwise the sanitized value.
+	 */
+	public function sanitize( $value ) {
+		// Menu is marked for deletion.
+		if ( false === $value ) {
+			return $value;
+		}
+
+		// Invalid.
+		if ( ! is_array( $value ) ) {
+			return null;
+		}
+
+		$default = array(
+			'name'        => '',
+			'description' => '',
+			'parent'      => 0,
+			'auto_add'    => false,
+		);
+		$value   = array_merge( $default, $value );
+		$value   = wp_array_slice_assoc( $value, array_keys( $default ) );
+
+		$value['name']        = trim( esc_html( $value['name'] ) ); // This sanitization code is used in wp-admin/nav-menus.php.
+		$value['description'] = sanitize_text_field( $value['description'] );
+		$value['parent']      = max( 0, (int) $value['parent'] );
+		$value['auto_add']    = ! empty( $value['auto_add'] );
+
+		if ( '' === $value['name'] ) {
+			$value['name'] = _x( '(unnamed)', 'Missing menu name.' );
+		}
+
+		/** This filter is documented in wp-includes/class-wp-customize-setting.php */
+		return apply_filters( "customize_sanitize_{$this->id}", $value, $this );
+	}
+
+	/**
+	 * Storage for data to be sent back to client in customize_save_response filter.
+	 *
+	 * See {@see 'customize_save_response'}.
+	 *
+	 * @since 4.3.0
+	 * @var array
+	 *
+	 * @see WP_Customize_Nav_Menu_Setting::amend_customize_save_response()
+	 */
+	protected $_widget_nav_menu_updates = array();
+
+	/**
+	 * Create/update the nav_menu term for this setting.
+	 *
+	 * Any created menus will have their assigned term IDs exported to the client
+	 * via the {@see 'customize_save_response'} filter. Likewise, any errors will be exported
+	 * to the client via the customize_save_response() filter.
+	 *
+	 * To delete a menu, the client can send false as the value.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see wp_update_nav_menu_object()
+	 *
+	 * @param array|false $value {
+	 *     The value to update. Note that slug cannot be updated via wp_update_nav_menu_object().
+	 *     If false, then the menu will be deleted entirely.
+	 *
+	 *     @type string $name        The name of the menu to save.
+	 *     @type string $description The term description. Default empty string.
+	 *     @type int    $parent      The id of the parent term. Default 0.
+	 *     @type bool   $auto_add    Whether pages will auto_add to this menu. Default false.
+	 * }
+	 * @return null|void
+	 */
+	protected function update( $value ) {
+		if ( $this->is_updated ) {
+			return;
+		}
+
+		$this->is_updated = true;
+		$is_placeholder   = ( $this->term_id < 0 );
+		$is_delete        = ( false === $value );
+
+		add_filter( 'customize_save_response', array( $this, 'amend_customize_save_response' ) );
+
+		$auto_add = null;
+		if ( $is_delete ) {
+			// If the current setting term is a placeholder, a delete request is a no-op.
+			if ( $is_placeholder ) {
+				$this->update_status = 'deleted';
+			} else {
+				$r = wp_delete_nav_menu( $this->term_id );
+
+				if ( is_wp_error( $r ) ) {
+					$this->update_status = 'error';
+					$this->update_error  = $r;
+				} else {
+					$this->update_status = 'deleted';
+					$auto_add            = false;
+				}
+			}
+		} else {
+			// Insert or update menu.
+			$menu_data              = wp_array_slice_assoc( $value, array( 'description', 'parent' ) );
+			$menu_data['menu-name'] = $value['name'];
+
+			$menu_id              = $is_placeholder ? 0 : $this->term_id;
+			$r                    = wp_update_nav_menu_object( $menu_id, wp_slash( $menu_data ) );
+			$original_name        = $menu_data['menu-name'];
+			$name_conflict_suffix = 1;
+			while ( is_wp_error( $r ) && 'menu_exists' === $r->get_error_code() ) {
+				$name_conflict_suffix += 1;
+				/* translators: 1: Original menu name, 2: Duplicate count. */
+				$menu_data['menu-name'] = sprintf( __( '%1$s (%2$d)' ), $original_name, $name_conflict_suffix );
+				$r                      = wp_update_nav_menu_object( $menu_id, wp_slash( $menu_data ) );
+			}
+
+			if ( is_wp_error( $r ) ) {
+				$this->update_status = 'error';
+				$this->update_error  = $r;
+			} else {
+				if ( $is_placeholder ) {
+					$this->previous_term_id = $this->term_id;
+					$this->term_id          = $r;
+					$this->update_status    = 'inserted';
+				} else {
+					$this->update_status = 'updated';
+				}
+
+				$auto_add = $value['auto_add'];
+			}
+		}
+
+		if ( null !== $auto_add ) {
+			$nav_menu_options = $this->filter_nav_menu_options_value(
+				(array) get_option( 'nav_menu_options', array() ),
+				$this->term_id,
+				$auto_add
+			);
+			update_option( 'nav_menu_options', $nav_menu_options );
+		}
+
+		if ( 'inserted' === $this->update_status ) {
+			// Make sure that new menus assigned to nav menu locations use their new IDs.
+			foreach ( $this->manager->settings() as $setting ) {
+				if ( ! preg_match( '/^nav_menu_locations\[/', $setting->id ) ) {
+					continue;
+				}
+
+				$post_value = $setting->post_value( null );
+				if ( ! is_null( $post_value ) && (int) $post_value === $this->previous_term_id ) {
+					$this->manager->set_post_value( $setting->id, $this->term_id );
+					$setting->save();
+				}
+			}
+
+			// Make sure that any nav_menu widgets referencing the placeholder nav menu get updated and sent back to client.
+			foreach ( array_keys( $this->manager->unsanitized_post_values() ) as $setting_id ) {
+				$nav_menu_widget_setting = $this->manager->get_setting( $setting_id );
+				if ( ! $nav_menu_widget_setting || ! preg_match( '/^widget_nav_menu\[/', $nav_menu_widget_setting->id ) ) {
+					continue;
+				}
+
+				$widget_instance = $nav_menu_widget_setting->post_value(); // Note that this calls WP_Customize_Widgets::sanitize_widget_instance().
+				if ( empty( $widget_instance['nav_menu'] ) || (int) $widget_instance['nav_menu'] !== $this->previous_term_id ) {
+					continue;
+				}
+
+				$widget_instance['nav_menu'] = $this->term_id;
+				$updated_widget_instance     = $this->manager->widgets->sanitize_widget_js_instance( $widget_instance );
+				$this->manager->set_post_value( $nav_menu_widget_setting->id, $updated_widget_instance );
+				$nav_menu_widget_setting->save();
+
+				$this->_widget_nav_menu_updates[ $nav_menu_widget_setting->id ] = $updated_widget_instance;
+			}
+		}
+	}
+
+	/**
+	 * Updates a nav_menu_options array.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Nav_Menu_Setting::filter_nav_menu_options()
+	 * @see WP_Customize_Nav_Menu_Setting::update()
+	 *
+	 * @param array $nav_menu_options Array as returned by get_option( 'nav_menu_options' ).
+	 * @param int   $menu_id          The term ID for the given menu.
+	 * @param bool  $auto_add         Whether to auto-add or not.
+	 * @return array (Maybe) modified nav_menu_options array.
+	 */
+	protected function filter_nav_menu_options_value( $nav_menu_options, $menu_id, $auto_add ) {
+		$nav_menu_options = (array) $nav_menu_options;
+		if ( ! isset( $nav_menu_options['auto_add'] ) ) {
+			$nav_menu_options['auto_add'] = array();
+		}
+
+		$i = array_search( $menu_id, $nav_menu_options['auto_add'], true );
+
+		if ( $auto_add && false === $i ) {
+			array_push( $nav_menu_options['auto_add'], $this->term_id );
+		} elseif ( ! $auto_add && false !== $i ) {
+			array_splice( $nav_menu_options['auto_add'], $i, 1 );
+		}
+
+		return $nav_menu_options;
+	}
+
+	/**
+	 * Export data for the JS client.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Nav_Menu_Setting::update()
+	 *
+	 * @param array $data Additional information passed back to the 'saved' event on `wp.customize`.
+	 * @return array Export data.
+	 */
+	public function amend_customize_save_response( $data ) {
+		if ( ! isset( $data['nav_menu_updates'] ) ) {
+			$data['nav_menu_updates'] = array();
+		}
+		if ( ! isset( $data['widget_nav_menu_updates'] ) ) {
+			$data['widget_nav_menu_updates'] = array();
+		}
+
+		$data['nav_menu_updates'][] = array(
+			'term_id'          => $this->term_id,
+			'previous_term_id' => $this->previous_term_id,
+			'error'            => $this->update_error ? $this->update_error->get_error_code() : null,
+			'status'           => $this->update_status,
+			'saved_value'      => 'deleted' === $this->update_status ? null : $this->value(),
+		);
+
+		$data['widget_nav_menu_updates'] = array_merge(
+			$data['widget_nav_menu_updates'],
+			$this->_widget_nav_menu_updates
+		);
+		$this->_widget_nav_menu_updates  = array();
+
+		return $data;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-nav-menus-panel.php b/wp-includes/customize/class-wp-customize-nav-menus-panel.php
new file mode 100644
index 0000000..0678fbf
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-nav-menus-panel.php
@@ -0,0 +1,116 @@
+<?php
+/**
+ * Customize API: WP_Customize_Nav_Menus_Panel class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Nav Menus Panel Class
+ *
+ * Needed to add screen options.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Panel
+ */
+class WP_Customize_Nav_Menus_Panel extends WP_Customize_Panel {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'nav_menus';
+
+	/**
+	 * Render screen options for Menus.
+	 *
+	 * @since 4.3.0
+	 */
+	public function render_screen_options() {
+		// Adds the screen options.
+		require_once ABSPATH . 'wp-admin/includes/nav-menu.php';
+		add_filter( 'manage_nav-menus_columns', 'wp_nav_menu_manage_columns' );
+
+		// Display screen options.
+		$screen = WP_Screen::get( 'nav-menus.php' );
+		$screen->render_screen_options( array( 'wrap' => false ) );
+	}
+
+	/**
+	 * Returns the advanced options for the nav menus page.
+	 *
+	 * Link title attribute added as it's a relatively advanced concept for new users.
+	 *
+	 * @since 4.3.0
+	 * @deprecated 4.5.0 Deprecated in favor of wp_nav_menu_manage_columns().
+	 */
+	public function wp_nav_menu_manage_columns() {
+		_deprecated_function( __METHOD__, '4.5.0', 'wp_nav_menu_manage_columns' );
+		require_once ABSPATH . 'wp-admin/includes/nav-menu.php';
+		return wp_nav_menu_manage_columns();
+	}
+
+	/**
+	 * An Underscore (JS) template for this panel's content (but not its container).
+	 *
+	 * Class variables for this panel class are available in the `data` JS object;
+	 * export custom variables by overriding WP_Customize_Panel::json().
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Panel::print_template()
+	 */
+	protected function content_template() {
+		?>
+		<li class="panel-meta customize-info accordion-section <# if ( ! data.description ) { #> cannot-expand<# } #>">
+			<button type="button" class="customize-panel-back" tabindex="-1">
+				<span class="screen-reader-text">
+					<?php
+					/* translators: Hidden accessibility text. */
+					_e( 'Back' );
+					?>
+				</span>
+			</button>
+			<div class="accordion-section-title">
+				<span class="preview-notice">
+					<?php
+					/* translators: %s: The site/panel title in the Customizer. */
+					printf( __( 'You are customizing %s' ), '<strong class="panel-title">{{ data.title }}</strong>' );
+					?>
+				</span>
+				<button type="button" class="customize-help-toggle dashicons dashicons-editor-help" aria-expanded="false">
+					<span class="screen-reader-text">
+						<?php
+						/* translators: Hidden accessibility text. */
+						_e( 'Help' );
+						?>
+					</span>
+				</button>
+				<button type="button" class="customize-screen-options-toggle" aria-expanded="false">
+					<span class="screen-reader-text">
+						<?php
+						/* translators: Hidden accessibility text. */
+						_e( 'Menu Options' );
+						?>
+					</span>
+				</button>
+			</div>
+			<# if ( data.description ) { #>
+			<div class="description customize-panel-description">{{{ data.description }}}</div>
+			<# } #>
+			<div id="screen-options-wrap">
+				<?php $this->render_screen_options(); ?>
+			</div>
+		</li>
+		<?php
+		// NOTE: The following is a workaround for an inability to treat (and thus label) a list of sections as a whole.
+		?>
+		<li class="customize-control-title customize-section-title-nav_menus-heading"><?php _e( 'Menus' ); ?></li>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-new-menu-control.php b/wp-includes/customize/class-wp-customize-new-menu-control.php
new file mode 100644
index 0000000..7dca284
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-new-menu-control.php
@@ -0,0 +1,63 @@
+<?php
+/**
+ * Customize API: WP_Customize_New_Menu_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ * @deprecated 4.9.0 This file is no longer used as of the menu creation UX introduced in #40104.
+ */
+
+_deprecated_file( basename( __FILE__ ), '4.9.0' );
+
+/**
+ * Customize control class for new menus.
+ *
+ * @since 4.3.0
+ * @deprecated 4.9.0 This class is no longer used as of the menu creation UX introduced in #40104.
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_New_Menu_Control extends WP_Customize_Control {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'new_menu';
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 4.9.0
+	 * @deprecated 4.9.0
+	 *
+	 * @see WP_Customize_Control::__construct()
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      The control ID.
+	 * @param array                $args    Optional. Arguments to override class property defaults.
+	 *                                      See WP_Customize_Control::__construct() for information
+	 *                                      on accepted arguments. Default empty array.
+	 */
+	public function __construct( WP_Customize_Manager $manager, $id, array $args = array() ) {
+		_deprecated_function( __METHOD__, '4.9.0' );
+		parent::__construct( $manager, $id, $args );
+	}
+
+	/**
+	 * Render the control's content.
+	 *
+	 * @since 4.3.0
+	 * @deprecated 4.9.0
+	 */
+	public function render_content() {
+		_deprecated_function( __METHOD__, '4.9.0' );
+		?>
+		<button type="button" class="button button-primary" id="create-new-menu-submit"><?php _e( 'Create Menu' ); ?></button>
+		<span class="spinner"></span>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-new-menu-section.php b/wp-includes/customize/class-wp-customize-new-menu-section.php
new file mode 100644
index 0000000..e9dc98f
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-new-menu-section.php
@@ -0,0 +1,65 @@
+<?php
+/**
+ * Customize API: WP_Customize_New_Menu_Section class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ * @deprecated 4.9.0 This file is no longer used as of the menu creation UX introduced in #40104.
+ */
+
+_deprecated_file( basename( __FILE__ ), '4.9.0' );
+
+/**
+ * Customize Menu Section Class
+ *
+ * @since 4.3.0
+ * @deprecated 4.9.0 This class is no longer used as of the menu creation UX introduced in #40104.
+ *
+ * @see WP_Customize_Section
+ */
+class WP_Customize_New_Menu_Section extends WP_Customize_Section {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'new_menu';
+
+	/**
+	 * Constructor.
+	 *
+	 * Any supplied $args override class property defaults.
+	 *
+	 * @since 4.9.0
+	 * @deprecated 4.9.0
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      A specific ID of the section.
+	 * @param array                $args    Section arguments.
+	 */
+	public function __construct( WP_Customize_Manager $manager, $id, array $args = array() ) {
+		_deprecated_function( __METHOD__, '4.9.0' );
+		parent::__construct( $manager, $id, $args );
+	}
+
+	/**
+	 * Render the section, and the controls that have been added to it.
+	 *
+	 * @since 4.3.0
+	 * @deprecated 4.9.0
+	 */
+	protected function render() {
+		_deprecated_function( __METHOD__, '4.9.0' );
+		?>
+		<li id="accordion-section-<?php echo esc_attr( $this->id ); ?>" class="accordion-section-new-menu">
+			<button type="button" class="button add-new-menu-item add-menu-toggle" aria-expanded="false">
+				<?php echo esc_html( $this->title ); ?>
+			</button>
+			<ul class="new-menu-section-content"></ul>
+		</li>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-partial.php b/wp-includes/customize/class-wp-customize-partial.php
new file mode 100644
index 0000000..06502be
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-partial.php
@@ -0,0 +1,330 @@
+<?php
+/**
+ * Customize API: WP_Customize_Partial class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.5.0
+ */
+
+/**
+ * Core Customizer class for implementing selective refresh partials.
+ *
+ * Representation of a rendered region in the previewed page that gets
+ * selectively refreshed when an associated setting is changed.
+ * This class is analogous of WP_Customize_Control.
+ *
+ * @since 4.5.0
+ */
+#[AllowDynamicProperties]
+class WP_Customize_Partial {
+
+	/**
+	 * Component.
+	 *
+	 * @since 4.5.0
+	 * @var WP_Customize_Selective_Refresh
+	 */
+	public $component;
+
+	/**
+	 * Unique identifier for the partial.
+	 *
+	 * If the partial is used to display a single setting, this would generally
+	 * be the same as the associated setting's ID.
+	 *
+	 * @since 4.5.0
+	 * @var string
+	 */
+	public $id;
+
+	/**
+	 * Parsed ID.
+	 *
+	 * @since 4.5.0
+	 * @var array {
+	 *     @type string $base ID base.
+	 *     @type array  $keys Keys for multidimensional.
+	 * }
+	 */
+	protected $id_data = array();
+
+	/**
+	 * Type of this partial.
+	 *
+	 * @since 4.5.0
+	 * @var string
+	 */
+	public $type = 'default';
+
+	/**
+	 * The jQuery selector to find the container element for the partial.
+	 *
+	 * @since 4.5.0
+	 * @var string
+	 */
+	public $selector;
+
+	/**
+	 * IDs for settings tied to the partial.
+	 *
+	 * @since 4.5.0
+	 * @var string[]
+	 */
+	public $settings;
+
+	/**
+	 * The ID for the setting that this partial is primarily responsible for rendering.
+	 *
+	 * If not supplied, it will default to the ID of the first setting.
+	 *
+	 * @since 4.5.0
+	 * @var string
+	 */
+	public $primary_setting;
+
+	/**
+	 * Capability required to edit this partial.
+	 *
+	 * Normally this is empty and the capability is derived from the capabilities
+	 * of the associated `$settings`.
+	 *
+	 * @since 4.5.0
+	 * @var string
+	 */
+	public $capability;
+
+	/**
+	 * Render callback.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @see WP_Customize_Partial::render()
+	 * @var callable Callback is called with one argument, the instance of
+	 *               WP_Customize_Partial. The callback can either echo the
+	 *               partial or return the partial as a string, or return false if error.
+	 */
+	public $render_callback;
+
+	/**
+	 * Whether the container element is included in the partial, or if only the contents are rendered.
+	 *
+	 * @since 4.5.0
+	 * @var bool
+	 */
+	public $container_inclusive = false;
+
+	/**
+	 * Whether to refresh the entire preview in case a partial cannot be refreshed.
+	 *
+	 * A partial render is considered a failure if the render_callback returns false.
+	 *
+	 * @since 4.5.0
+	 * @var bool
+	 */
+	public $fallback_refresh = true;
+
+	/**
+	 * Constructor.
+	 *
+	 * Supplied `$args` override class property defaults.
+	 *
+	 * If `$args['settings']` is not defined, use the $id as the setting ID.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @param WP_Customize_Selective_Refresh $component Customize Partial Refresh plugin instance.
+	 * @param string                         $id        Control ID.
+	 * @param array                          $args {
+	 *     Optional. Array of properties for the new Partials object. Default empty array.
+	 *
+	 *     @type string   $type                  Type of the partial to be created.
+	 *     @type string   $selector              The jQuery selector to find the container element for the partial, that is,
+	 *                                           a partial's placement.
+	 *     @type string[] $settings              IDs for settings tied to the partial. If undefined, `$id` will be used.
+	 *     @type string   $primary_setting       The ID for the setting that this partial is primarily responsible for
+	 *                                           rendering. If not supplied, it will default to the ID of the first setting.
+	 *     @type string   $capability            Capability required to edit this partial.
+	 *                                           Normally this is empty and the capability is derived from the capabilities
+	 *                                           of the associated `$settings`.
+	 *     @type callable $render_callback       Render callback.
+	 *                                           Callback is called with one argument, the instance of WP_Customize_Partial.
+	 *                                           The callback can either echo the partial or return the partial as a string,
+	 *                                           or return false if error.
+	 *     @type bool     $container_inclusive   Whether the container element is included in the partial, or if only
+	 *                                           the contents are rendered.
+	 *     @type bool     $fallback_refresh      Whether to refresh the entire preview in case a partial cannot be refreshed.
+	 *                                           A partial render is considered a failure if the render_callback returns
+	 *                                           false.
+	 * }
+	 */
+	public function __construct( WP_Customize_Selective_Refresh $component, $id, $args = array() ) {
+		$keys = array_keys( get_object_vars( $this ) );
+		foreach ( $keys as $key ) {
+			if ( isset( $args[ $key ] ) ) {
+				$this->$key = $args[ $key ];
+			}
+		}
+
+		$this->component       = $component;
+		$this->id              = $id;
+		$this->id_data['keys'] = preg_split( '/\[/', str_replace( ']', '', $this->id ) );
+		$this->id_data['base'] = array_shift( $this->id_data['keys'] );
+
+		if ( empty( $this->render_callback ) ) {
+			$this->render_callback = array( $this, 'render_callback' );
+		}
+
+		// Process settings.
+		if ( ! isset( $this->settings ) ) {
+			$this->settings = array( $id );
+		} elseif ( is_string( $this->settings ) ) {
+			$this->settings = array( $this->settings );
+		}
+
+		if ( empty( $this->primary_setting ) ) {
+			$this->primary_setting = current( $this->settings );
+		}
+	}
+
+	/**
+	 * Retrieves parsed ID data for multidimensional setting.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @return array {
+	 *     ID data for multidimensional partial.
+	 *
+	 *     @type string $base ID base.
+	 *     @type array  $keys Keys for multidimensional array.
+	 * }
+	 */
+	final public function id_data() {
+		return $this->id_data;
+	}
+
+	/**
+	 * Renders the template partial involving the associated settings.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @param array $container_context Optional. Array of context data associated with the target container (placement).
+	 *                                 Default empty array.
+	 * @return string|array|false The rendered partial as a string, raw data array (for client-side JS template),
+	 *                            or false if no render applied.
+	 */
+	final public function render( $container_context = array() ) {
+		$partial  = $this;
+		$rendered = false;
+
+		if ( ! empty( $this->render_callback ) ) {
+			ob_start();
+			$return_render = call_user_func( $this->render_callback, $this, $container_context );
+			$ob_render     = ob_get_clean();
+
+			if ( null !== $return_render && '' !== $ob_render ) {
+				_doing_it_wrong( __FUNCTION__, __( 'Partial render must echo the content or return the content string (or array), but not both.' ), '4.5.0' );
+			}
+
+			/*
+			 * Note that the string return takes precedence because the $ob_render may just\
+			 * include PHP warnings or notices.
+			 */
+			$rendered = null !== $return_render ? $return_render : $ob_render;
+		}
+
+		/**
+		 * Filters partial rendering.
+		 *
+		 * @since 4.5.0
+		 *
+		 * @param string|array|false   $rendered          The partial value. Default false.
+		 * @param WP_Customize_Partial $partial           WP_Customize_Setting instance.
+		 * @param array                $container_context Optional array of context data associated with
+		 *                                                the target container.
+		 */
+		$rendered = apply_filters( 'customize_partial_render', $rendered, $partial, $container_context );
+
+		/**
+		 * Filters partial rendering for a specific partial.
+		 *
+		 * The dynamic portion of the hook name, `$partial->ID` refers to the partial ID.
+		 *
+		 * @since 4.5.0
+		 *
+		 * @param string|array|false   $rendered          The partial value. Default false.
+		 * @param WP_Customize_Partial $partial           WP_Customize_Setting instance.
+		 * @param array                $container_context Optional array of context data associated with
+		 *                                                the target container.
+		 */
+		$rendered = apply_filters( "customize_partial_render_{$partial->id}", $rendered, $partial, $container_context );
+
+		return $rendered;
+	}
+
+	/**
+	 * Default callback used when invoking WP_Customize_Control::render().
+	 *
+	 * Note that this method may echo the partial *or* return the partial as
+	 * a string or array, but not both. Output buffering is performed when this
+	 * is called. Subclasses can override this with their specific logic, or they
+	 * may provide an 'render_callback' argument to the constructor.
+	 *
+	 * This method may return an HTML string for straight DOM injection, or it
+	 * may return an array for supporting Partial JS subclasses to render by
+	 * applying to client-side templating.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @param WP_Customize_Partial $partial Partial.
+	 * @param array                $context Context.
+	 * @return string|array|false
+	 */
+	public function render_callback( WP_Customize_Partial $partial, $context = array() ) {
+		unset( $partial, $context );
+		return false;
+	}
+
+	/**
+	 * Retrieves the data to export to the client via JSON.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @return array Array of parameters passed to the JavaScript.
+	 */
+	public function json() {
+		$exports = array(
+			'settings'           => $this->settings,
+			'primarySetting'     => $this->primary_setting,
+			'selector'           => $this->selector,
+			'type'               => $this->type,
+			'fallbackRefresh'    => $this->fallback_refresh,
+			'containerInclusive' => $this->container_inclusive,
+		);
+		return $exports;
+	}
+
+	/**
+	 * Checks if the user can refresh this partial.
+	 *
+	 * Returns false if the user cannot manipulate one of the associated settings,
+	 * or if one of the associated settings does not exist.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @return bool False if user can't edit one of the related settings,
+	 *                    or if one of the associated settings does not exist.
+	 */
+	final public function check_capabilities() {
+		if ( ! empty( $this->capability ) && ! current_user_can( $this->capability ) ) {
+			return false;
+		}
+		foreach ( $this->settings as $setting_id ) {
+			$setting = $this->component->manager->get_setting( $setting_id );
+			if ( ! $setting || ! $setting->check_capabilities() ) {
+				return false;
+			}
+		}
+		return true;
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-selective-refresh.php b/wp-includes/customize/class-wp-customize-selective-refresh.php
new file mode 100644
index 0000000..d20e8ab
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-selective-refresh.php
@@ -0,0 +1,441 @@
+<?php
+/**
+ * Customize API: WP_Customize_Selective_Refresh class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.5.0
+ */
+
+/**
+ * Core Customizer class for implementing selective refresh.
+ *
+ * @since 4.5.0
+ */
+#[AllowDynamicProperties]
+final class WP_Customize_Selective_Refresh {
+
+	/**
+	 * Query var used in requests to render partials.
+	 *
+	 * @since 4.5.0
+	 */
+	const RENDER_QUERY_VAR = 'wp_customize_render_partials';
+
+	/**
+	 * Customize manager.
+	 *
+	 * @since 4.5.0
+	 * @var WP_Customize_Manager
+	 */
+	public $manager;
+
+	/**
+	 * Registered instances of WP_Customize_Partial.
+	 *
+	 * @since 4.5.0
+	 * @var WP_Customize_Partial[]
+	 */
+	protected $partials = array();
+
+	/**
+	 * Log of errors triggered when partials are rendered.
+	 *
+	 * @since 4.5.0
+	 * @var array
+	 */
+	protected $triggered_errors = array();
+
+	/**
+	 * Keep track of the current partial being rendered.
+	 *
+	 * @since 4.5.0
+	 * @var string|null
+	 */
+	protected $current_partial_id;
+
+	/**
+	 * Plugin bootstrap for Partial Refresh functionality.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 */
+	public function __construct( WP_Customize_Manager $manager ) {
+		$this->manager = $manager;
+		require_once ABSPATH . WPINC . '/customize/class-wp-customize-partial.php';
+
+		add_action( 'customize_preview_init', array( $this, 'init_preview' ) );
+	}
+
+	/**
+	 * Retrieves the registered partials.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @return array Partials.
+	 */
+	public function partials() {
+		return $this->partials;
+	}
+
+	/**
+	 * Adds a partial.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @see WP_Customize_Partial::__construct()
+	 *
+	 * @param WP_Customize_Partial|string $id   Customize Partial object, or Partial ID.
+	 * @param array                       $args Optional. Array of properties for the new Partials object.
+	 *                                          See WP_Customize_Partial::__construct() for information
+	 *                                          on accepted arguments. Default empty array.
+	 * @return WP_Customize_Partial The instance of the partial that was added.
+	 */
+	public function add_partial( $id, $args = array() ) {
+		if ( $id instanceof WP_Customize_Partial ) {
+			$partial = $id;
+		} else {
+			$class = 'WP_Customize_Partial';
+
+			/** This filter is documented in wp-includes/customize/class-wp-customize-selective-refresh.php */
+			$args = apply_filters( 'customize_dynamic_partial_args', $args, $id );
+
+			/** This filter is documented in wp-includes/customize/class-wp-customize-selective-refresh.php */
+			$class = apply_filters( 'customize_dynamic_partial_class', $class, $id, $args );
+
+			$partial = new $class( $this, $id, $args );
+		}
+
+		$this->partials[ $partial->id ] = $partial;
+		return $partial;
+	}
+
+	/**
+	 * Retrieves a partial.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @param string $id Customize Partial ID.
+	 * @return WP_Customize_Partial|null The partial, if set. Otherwise null.
+	 */
+	public function get_partial( $id ) {
+		if ( isset( $this->partials[ $id ] ) ) {
+			return $this->partials[ $id ];
+		} else {
+			return null;
+		}
+	}
+
+	/**
+	 * Removes a partial.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @param string $id Customize Partial ID.
+	 */
+	public function remove_partial( $id ) {
+		unset( $this->partials[ $id ] );
+	}
+
+	/**
+	 * Initializes the Customizer preview.
+	 *
+	 * @since 4.5.0
+	 */
+	public function init_preview() {
+		add_action( 'template_redirect', array( $this, 'handle_render_partials_request' ) );
+		add_action( 'wp_enqueue_scripts', array( $this, 'enqueue_preview_scripts' ) );
+	}
+
+	/**
+	 * Enqueues preview scripts.
+	 *
+	 * @since 4.5.0
+	 */
+	public function enqueue_preview_scripts() {
+		wp_enqueue_script( 'customize-selective-refresh' );
+		add_action( 'wp_footer', array( $this, 'export_preview_data' ), 1000 );
+	}
+
+	/**
+	 * Exports data in preview after it has finished rendering so that partials can be added at runtime.
+	 *
+	 * @since 4.5.0
+	 */
+	public function export_preview_data() {
+		$partials = array();
+
+		foreach ( $this->partials() as $partial ) {
+			if ( $partial->check_capabilities() ) {
+				$partials[ $partial->id ] = $partial->json();
+			}
+		}
+
+		$switched_locale = switch_to_user_locale( get_current_user_id() );
+		$l10n            = array(
+			'shiftClickToEdit' => __( 'Shift-click to edit this element.' ),
+			'clickEditMenu'    => __( 'Click to edit this menu.' ),
+			'clickEditWidget'  => __( 'Click to edit this widget.' ),
+			'clickEditTitle'   => __( 'Click to edit the site title.' ),
+			'clickEditMisc'    => __( 'Click to edit this element.' ),
+			/* translators: %s: document.write() */
+			'badDocumentWrite' => sprintf( __( '%s is forbidden' ), 'document.write()' ),
+		);
+		if ( $switched_locale ) {
+			restore_previous_locale();
+		}
+
+		$exports = array(
+			'partials'       => $partials,
+			'renderQueryVar' => self::RENDER_QUERY_VAR,
+			'l10n'           => $l10n,
+		);
+
+		// Export data to JS.
+		wp_print_inline_script_tag( sprintf( 'var _customizePartialRefreshExports = %s;', wp_json_encode( $exports ) ) );
+	}
+
+	/**
+	 * Registers dynamically-created partials.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @see WP_Customize_Manager::add_dynamic_settings()
+	 *
+	 * @param string[] $partial_ids Array of the partial IDs to add.
+	 * @return WP_Customize_Partial[] Array of added WP_Customize_Partial instances.
+	 */
+	public function add_dynamic_partials( $partial_ids ) {
+		$new_partials = array();
+
+		foreach ( $partial_ids as $partial_id ) {
+
+			// Skip partials already created.
+			$partial = $this->get_partial( $partial_id );
+			if ( $partial ) {
+				continue;
+			}
+
+			$partial_args  = false;
+			$partial_class = 'WP_Customize_Partial';
+
+			/**
+			 * Filters a dynamic partial's constructor arguments.
+			 *
+			 * For a dynamic partial to be registered, this filter must be employed
+			 * to override the default false value with an array of args to pass to
+			 * the WP_Customize_Partial constructor.
+			 *
+			 * @since 4.5.0
+			 *
+			 * @param false|array $partial_args The arguments to the WP_Customize_Partial constructor.
+			 * @param string      $partial_id   ID for dynamic partial.
+			 */
+			$partial_args = apply_filters( 'customize_dynamic_partial_args', $partial_args, $partial_id );
+			if ( false === $partial_args ) {
+				continue;
+			}
+
+			/**
+			 * Filters the class used to construct partials.
+			 *
+			 * Allow non-statically created partials to be constructed with custom WP_Customize_Partial subclass.
+			 *
+			 * @since 4.5.0
+			 *
+			 * @param string $partial_class WP_Customize_Partial or a subclass.
+			 * @param string $partial_id    ID for dynamic partial.
+			 * @param array  $partial_args  The arguments to the WP_Customize_Partial constructor.
+			 */
+			$partial_class = apply_filters( 'customize_dynamic_partial_class', $partial_class, $partial_id, $partial_args );
+
+			$partial = new $partial_class( $this, $partial_id, $partial_args );
+
+			$this->add_partial( $partial );
+			$new_partials[] = $partial;
+		}
+		return $new_partials;
+	}
+
+	/**
+	 * Checks whether the request is for rendering partials.
+	 *
+	 * Note that this will not consider whether the request is authorized or valid,
+	 * just that essentially the route is a match.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @return bool Whether the request is for rendering partials.
+	 */
+	public function is_render_partials_request() {
+		return ! empty( $_POST[ self::RENDER_QUERY_VAR ] );
+	}
+
+	/**
+	 * Handles PHP errors triggered during rendering the partials.
+	 *
+	 * These errors will be relayed back to the client in the Ajax response.
+	 *
+	 * @since 4.5.0
+	 *
+	 * @param int    $errno   Error number.
+	 * @param string $errstr  Error string.
+	 * @param string $errfile Error file.
+	 * @param int    $errline Error line.
+	 * @return true Always true.
+	 */
+	public function handle_error( $errno, $errstr, $errfile = null, $errline = null ) {
+		$this->triggered_errors[] = array(
+			'partial'      => $this->current_partial_id,
+			'error_number' => $errno,
+			'error_string' => $errstr,
+			'error_file'   => $errfile,
+			'error_line'   => $errline,
+		);
+		return true;
+	}
+
+	/**
+	 * Handles the Ajax request to return the rendered partials for the requested placements.
+	 *
+	 * @since 4.5.0
+	 */
+	public function handle_render_partials_request() {
+		if ( ! $this->is_render_partials_request() ) {
+			return;
+		}
+
+		/*
+		 * Note that is_customize_preview() returning true will entail that the
+		 * user passed the 'customize' capability check and the nonce check, since
+		 * WP_Customize_Manager::setup_theme() is where the previewing flag is set.
+		 */
+		if ( ! is_customize_preview() ) {
+			wp_send_json_error( 'expected_customize_preview', 403 );
+		} elseif ( ! isset( $_POST['partials'] ) ) {
+			wp_send_json_error( 'missing_partials', 400 );
+		}
+
+		// Ensure that doing selective refresh on 404 template doesn't result in fallback rendering behavior (full refreshes).
+		status_header( 200 );
+
+		$partials = json_decode( wp_unslash( $_POST['partials'] ), true );
+
+		if ( ! is_array( $partials ) ) {
+			wp_send_json_error( 'malformed_partials' );
+		}
+
+		$this->add_dynamic_partials( array_keys( $partials ) );
+
+		/**
+		 * Fires immediately before partials are rendered.
+		 *
+		 * Plugins may do things like call wp_enqueue_scripts() and gather a list of the scripts
+		 * and styles which may get enqueued in the response.
+		 *
+		 * @since 4.5.0
+		 *
+		 * @param WP_Customize_Selective_Refresh $refresh  Selective refresh component.
+		 * @param array                          $partials Placements' context data for the partials rendered in the request.
+		 *                                                 The array is keyed by partial ID, with each item being an array of
+		 *                                                 the placements' context data.
+		 */
+		do_action( 'customize_render_partials_before', $this, $partials );
+
+		set_error_handler( array( $this, 'handle_error' ), error_reporting() );
+
+		$contents = array();
+
+		foreach ( $partials as $partial_id => $container_contexts ) {
+			$this->current_partial_id = $partial_id;
+
+			if ( ! is_array( $container_contexts ) ) {
+				wp_send_json_error( 'malformed_container_contexts' );
+			}
+
+			$partial = $this->get_partial( $partial_id );
+
+			if ( ! $partial || ! $partial->check_capabilities() ) {
+				$contents[ $partial_id ] = null;
+				continue;
+			}
+
+			$contents[ $partial_id ] = array();
+
+			// @todo The array should include not only the contents, but also whether the container is included?
+			if ( empty( $container_contexts ) ) {
+				// Since there are no container contexts, render just once.
+				$contents[ $partial_id ][] = $partial->render( null );
+			} else {
+				foreach ( $container_contexts as $container_context ) {
+					$contents[ $partial_id ][] = $partial->render( $container_context );
+				}
+			}
+		}
+		$this->current_partial_id = null;
+
+		restore_error_handler();
+
+		/**
+		 * Fires immediately after partials are rendered.
+		 *
+		 * Plugins may do things like call wp_footer() to scrape scripts output and return them
+		 * via the {@see 'customize_render_partials_response'} filter.
+		 *
+		 * @since 4.5.0
+		 *
+		 * @param WP_Customize_Selective_Refresh $refresh  Selective refresh component.
+		 * @param array                          $partials Placements' context data for the partials rendered in the request.
+		 *                                                 The array is keyed by partial ID, with each item being an array of
+		 *                                                 the placements' context data.
+		 */
+		do_action( 'customize_render_partials_after', $this, $partials );
+
+		$response = array(
+			'contents' => $contents,
+		);
+
+		if ( defined( 'WP_DEBUG_DISPLAY' ) && WP_DEBUG_DISPLAY ) {
+			$response['errors'] = $this->triggered_errors;
+		}
+
+		$setting_validities             = $this->manager->validate_setting_values( $this->manager->unsanitized_post_values() );
+		$exported_setting_validities    = array_map( array( $this->manager, 'prepare_setting_validity_for_js' ), $setting_validities );
+		$response['setting_validities'] = $exported_setting_validities;
+
+		/**
+		 * Filters the response from rendering the partials.
+		 *
+		 * Plugins may use this filter to inject `$scripts` and `$styles`, which are dependencies
+		 * for the partials being rendered. The response data will be available to the client via
+		 * the `render-partials-response` JS event, so the client can then inject the scripts and
+		 * styles into the DOM if they have not already been enqueued there.
+		 *
+		 * If plugins do this, they'll need to take care for any scripts that do `document.write()`
+		 * and make sure that these are not injected, or else to override the function to no-op,
+		 * or else the page will be destroyed.
+		 *
+		 * Plugins should be aware that `$scripts` and `$styles` may eventually be included by
+		 * default in the response.
+		 *
+		 * @since 4.5.0
+		 *
+		 * @param array $response {
+		 *     Response.
+		 *
+		 *     @type array $contents Associative array mapping a partial ID its corresponding array of contents
+		 *                           for the containers requested.
+		 *     @type array $errors   List of errors triggered during rendering of partials, if `WP_DEBUG_DISPLAY`
+		 *                           is enabled.
+		 * }
+		 * @param WP_Customize_Selective_Refresh $refresh  Selective refresh component.
+		 * @param array                          $partials Placements' context data for the partials rendered in the request.
+		 *                                                 The array is keyed by partial ID, with each item being an array of
+		 *                                                 the placements' context data.
+		 */
+		$response = apply_filters( 'customize_render_partials_response', $response, $this, $partials );
+
+		wp_send_json_success( $response );
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-sidebar-section.php b/wp-includes/customize/class-wp-customize-sidebar-section.php
new file mode 100644
index 0000000..1d048b6
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-sidebar-section.php
@@ -0,0 +1,58 @@
+<?php
+/**
+ * Customize API: WP_Customize_Sidebar_Section class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customizer section representing widget area (sidebar).
+ *
+ * @since 4.1.0
+ *
+ * @see WP_Customize_Section
+ */
+class WP_Customize_Sidebar_Section extends WP_Customize_Section {
+
+	/**
+	 * Type of this section.
+	 *
+	 * @since 4.1.0
+	 * @var string
+	 */
+	public $type = 'sidebar';
+
+	/**
+	 * Unique identifier.
+	 *
+	 * @since 4.1.0
+	 * @var string
+	 */
+	public $sidebar_id;
+
+	/**
+	 * Gather the parameters passed to client JavaScript via JSON.
+	 *
+	 * @since 4.1.0
+	 *
+	 * @return array The array to be exported to the client as JSON.
+	 */
+	public function json() {
+		$json              = parent::json();
+		$json['sidebarId'] = $this->sidebar_id;
+		return $json;
+	}
+
+	/**
+	 * Whether the current sidebar is rendered on the page.
+	 *
+	 * @since 4.1.0
+	 *
+	 * @return bool Whether sidebar is rendered.
+	 */
+	public function active_callback() {
+		return $this->manager->widgets->is_sidebar_rendered( $this->sidebar_id );
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-site-icon-control.php b/wp-includes/customize/class-wp-customize-site-icon-control.php
new file mode 100644
index 0000000..942000a
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-site-icon-control.php
@@ -0,0 +1,97 @@
+<?php
+/**
+ * Customize API: WP_Customize_Site_Icon_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Site Icon control class.
+ *
+ * Used only for custom functionality in JavaScript.
+ *
+ * @since 4.3.0
+ *
+ * @see WP_Customize_Cropped_Image_Control
+ */
+class WP_Customize_Site_Icon_Control extends WP_Customize_Cropped_Image_Control {
+
+	/**
+	 * Control type.
+	 *
+	 * @since 4.3.0
+	 * @var string
+	 */
+	public $type = 'site_icon';
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 4.3.0
+	 *
+	 * @see WP_Customize_Control::__construct()
+	 *
+	 * @param WP_Customize_Manager $manager Customizer bootstrap instance.
+	 * @param string               $id      Control ID.
+	 * @param array                $args    Optional. Arguments to override class property defaults.
+	 *                                      See WP_Customize_Control::__construct() for information
+	 *                                      on accepted arguments. Default empty array.
+	 */
+	public function __construct( $manager, $id, $args = array() ) {
+		parent::__construct( $manager, $id, $args );
+		add_action( 'customize_controls_print_styles', 'wp_site_icon', 99 );
+	}
+
+	/**
+	 * Renders a JS template for the content of the site icon control.
+	 *
+	 * @since 4.5.0
+	 */
+	public function content_template() {
+		?>
+		<# if ( data.label ) { #>
+			<span class="customize-control-title">{{ data.label }}</span>
+		<# } #>
+		<# if ( data.description ) { #>
+			<span class="description customize-control-description">{{{ data.description }}}</span>
+		<# } #>
+
+		<# if ( data.attachment && data.attachment.id ) { #>
+			<div class="attachment-media-view">
+				<# if ( data.attachment.sizes ) { #>
+					<div class="site-icon-preview wp-clearfix">
+						<div class="favicon-preview">
+							<img src="<?php echo esc_url( admin_url( 'images/' . ( is_rtl() ? 'browser-rtl.png' : 'browser.png' ) ) ); ?>" class="browser-preview" width="182" alt="" />
+
+							<div class="favicon">
+								<img src="{{ data.attachment.sizes.full ? data.attachment.sizes.full.url : data.attachment.url }}" alt="<?php esc_attr_e( 'Preview as a browser icon' ); ?>" />
+							</div>
+							<span class="browser-title" aria-hidden="true"><# print( '<?php echo esc_js( get_bloginfo( 'name' ) ); ?>' ) #></span>
+						</div>
+						<img class="app-icon-preview" src="{{ data.attachment.sizes.full ? data.attachment.sizes.full.url : data.attachment.url }}" alt="<?php esc_attr_e( 'Preview as an app icon' ); ?>" />
+					</div>
+				<# } #>
+				<div class="actions">
+					<# if ( data.canUpload ) { #>
+						<button type="button" class="button remove-button"><?php echo $this->button_labels['remove']; ?></button>
+						<button type="button" class="button upload-button"><?php echo $this->button_labels['change']; ?></button>
+					<# } #>
+				</div>
+			</div>
+		<# } else { #>
+			<div class="attachment-media-view">
+				<# if ( data.canUpload ) { #>
+					<button type="button" class="upload-button button-add-media"><?php echo $this->button_labels['site_icon']; ?></button>
+				<# } #>
+				<div class="actions">
+					<# if ( data.defaultAttachment ) { #>
+						<button type="button" class="button default-button"><?php echo $this->button_labels['default']; ?></button>
+					<# } #>
+				</div>
+			</div>
+		<# } #>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-theme-control.php b/wp-includes/customize/class-wp-customize-theme-control.php
new file mode 100644
index 0000000..81c36dd
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-theme-control.php
@@ -0,0 +1,322 @@
+<?php
+/**
+ * Customize API: WP_Customize_Theme_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Theme Control class.
+ *
+ * @since 4.2.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Customize_Theme_Control extends WP_Customize_Control {
+
+	/**
+	 * Customize control type.
+	 *
+	 * @since 4.2.0
+	 * @var string
+	 */
+	public $type = 'theme';
+
+	/**
+	 * Theme object.
+	 *
+	 * @since 4.2.0
+	 * @var WP_Theme
+	 */
+	public $theme;
+
+	/**
+	 * Refresh the parameters passed to the JavaScript via JSON.
+	 *
+	 * @since 4.2.0
+	 *
+	 * @see WP_Customize_Control::to_json()
+	 */
+	public function to_json() {
+		parent::to_json();
+		$this->json['theme'] = $this->theme;
+	}
+
+	/**
+	 * Don't render the control content from PHP, as it's rendered via JS on load.
+	 *
+	 * @since 4.2.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * Render a JS template for theme display.
+	 *
+	 * @since 4.2.0
+	 */
+	public function content_template() {
+		/* translators: %s: Theme name. */
+		$details_label = sprintf( __( 'Details for theme: %s' ), '{{ data.theme.name }}' );
+		/* translators: %s: Theme name. */
+		$customize_label = sprintf( __( 'Customize theme: %s' ), '{{ data.theme.name }}' );
+		/* translators: %s: Theme name. */
+		$preview_label = sprintf( __( 'Live preview theme: %s' ), '{{ data.theme.name }}' );
+		/* translators: %s: Theme name. */
+		$install_label = sprintf( __( 'Install and preview theme: %s' ), '{{ data.theme.name }}' );
+		?>
+		<# if ( data.theme.active ) { #>
+			<div class="theme active" tabindex="0" aria-describedby="{{ data.section }}-{{ data.theme.id }}-action">
+		<# } else { #>
+			<div class="theme" tabindex="0" aria-describedby="{{ data.section }}-{{ data.theme.id }}-action">
+		<# } #>
+
+			<# if ( data.theme.screenshot && data.theme.screenshot[0] ) { #>
+				<div class="theme-screenshot">
+					<img data-src="{{ data.theme.screenshot[0] }}?ver={{ data.theme.version }}" alt="" />
+				</div>
+			<# } else { #>
+				<div class="theme-screenshot blank"></div>
+			<# } #>
+
+			<span class="more-details theme-details" id="{{ data.section }}-{{ data.theme.id }}-action" aria-label="<?php echo esc_attr( $details_label ); ?>"><?php _e( 'Theme Details' ); ?></span>
+
+			<div class="theme-author">
+			<?php
+				/* translators: Theme author name. */
+				printf( _x( 'By %s', 'theme author' ), '{{ data.theme.author }}' );
+			?>
+			</div>
+
+			<# if ( 'installed' === data.theme.type && data.theme.hasUpdate ) { #>
+				<# if ( data.theme.updateResponse.compatibleWP && data.theme.updateResponse.compatiblePHP ) { #>
+					<div class="update-message notice inline notice-warning notice-alt" data-slug="{{ data.theme.id }}">
+						<p>
+							<?php
+							if ( is_multisite() ) {
+								_e( 'New version available.' );
+							} else {
+								printf(
+									/* translators: %s: "Update now" button. */
+									__( 'New version available. %s' ),
+									'<button class="button-link update-theme" type="button">' . __( 'Update now' ) . '</button>'
+								);
+							}
+							?>
+						</p>
+					</div>
+				<# } else { #>
+					<div class="update-message notice inline notice-error notice-alt" data-slug="{{ data.theme.id }}">
+						<p>
+							<# if ( ! data.theme.updateResponse.compatibleWP && ! data.theme.updateResponse.compatiblePHP ) { #>
+								<?php
+								printf(
+									/* translators: %s: Theme name. */
+									__( 'There is a new version of %s available, but it does not work with your versions of WordPress and PHP.' ),
+									'{{{ data.theme.name }}}'
+								);
+								if ( current_user_can( 'update_core' ) && current_user_can( 'update_php' ) ) {
+									printf(
+										/* translators: 1: URL to WordPress Updates screen, 2: URL to Update PHP page. */
+										' ' . __( '<a href="%1$s">Please update WordPress</a>, and then <a href="%2$s">learn more about updating PHP</a>.' ),
+										self_admin_url( 'update-core.php' ),
+										esc_url( wp_get_update_php_url() )
+									);
+									wp_update_php_annotation( '</p><p><em>', '</em>' );
+								} elseif ( current_user_can( 'update_core' ) ) {
+									printf(
+										/* translators: %s: URL to WordPress Updates screen. */
+										' ' . __( '<a href="%s">Please update WordPress</a>.' ),
+										self_admin_url( 'update-core.php' )
+									);
+								} elseif ( current_user_can( 'update_php' ) ) {
+									printf(
+										/* translators: %s: URL to Update PHP page. */
+										' ' . __( '<a href="%s">Learn more about updating PHP</a>.' ),
+										esc_url( wp_get_update_php_url() )
+									);
+									wp_update_php_annotation( '</p><p><em>', '</em>' );
+								}
+								?>
+							<# } else if ( ! data.theme.updateResponse.compatibleWP ) { #>
+								<?php
+								printf(
+									/* translators: %s: Theme name. */
+									__( 'There is a new version of %s available, but it does not work with your version of WordPress.' ),
+									'{{{ data.theme.name }}}'
+								);
+								if ( current_user_can( 'update_core' ) ) {
+									printf(
+										/* translators: %s: URL to WordPress Updates screen. */
+										' ' . __( '<a href="%s">Please update WordPress</a>.' ),
+										self_admin_url( 'update-core.php' )
+									);
+								}
+								?>
+							<# } else if ( ! data.theme.updateResponse.compatiblePHP ) { #>
+								<?php
+								printf(
+									/* translators: %s: Theme name. */
+									__( 'There is a new version of %s available, but it does not work with your version of PHP.' ),
+									'{{{ data.theme.name }}}'
+								);
+								if ( current_user_can( 'update_php' ) ) {
+									printf(
+										/* translators: %s: URL to Update PHP page. */
+										' ' . __( '<a href="%s">Learn more about updating PHP</a>.' ),
+										esc_url( wp_get_update_php_url() )
+									);
+									wp_update_php_annotation( '</p><p><em>', '</em>' );
+								}
+								?>
+							<# } #>
+						</p>
+					</div>
+				<# } #>
+			<# } #>
+
+			<# if ( ! data.theme.compatibleWP || ! data.theme.compatiblePHP ) { #>
+				<div class="notice notice-error notice-alt"><p>
+					<# if ( ! data.theme.compatibleWP && ! data.theme.compatiblePHP ) { #>
+						<?php
+						_e( 'This theme does not work with your versions of WordPress and PHP.' );
+						if ( current_user_can( 'update_core' ) && current_user_can( 'update_php' ) ) {
+							printf(
+								/* translators: 1: URL to WordPress Updates screen, 2: URL to Update PHP page. */
+								' ' . __( '<a href="%1$s">Please update WordPress</a>, and then <a href="%2$s">learn more about updating PHP</a>.' ),
+								self_admin_url( 'update-core.php' ),
+								esc_url( wp_get_update_php_url() )
+							);
+							wp_update_php_annotation( '</p><p><em>', '</em>' );
+						} elseif ( current_user_can( 'update_core' ) ) {
+							printf(
+								/* translators: %s: URL to WordPress Updates screen. */
+								' ' . __( '<a href="%s">Please update WordPress</a>.' ),
+								self_admin_url( 'update-core.php' )
+							);
+						} elseif ( current_user_can( 'update_php' ) ) {
+							printf(
+								/* translators: %s: URL to Update PHP page. */
+								' ' . __( '<a href="%s">Learn more about updating PHP</a>.' ),
+								esc_url( wp_get_update_php_url() )
+							);
+							wp_update_php_annotation( '</p><p><em>', '</em>' );
+						}
+						?>
+					<# } else if ( ! data.theme.compatibleWP ) { #>
+						<?php
+						_e( 'This theme does not work with your version of WordPress.' );
+						if ( current_user_can( 'update_core' ) ) {
+							printf(
+								/* translators: %s: URL to WordPress Updates screen. */
+								' ' . __( '<a href="%s">Please update WordPress</a>.' ),
+								self_admin_url( 'update-core.php' )
+							);
+						}
+						?>
+					<# } else if ( ! data.theme.compatiblePHP ) { #>
+						<?php
+						_e( 'This theme does not work with your version of PHP.' );
+						if ( current_user_can( 'update_php' ) ) {
+							printf(
+								/* translators: %s: URL to Update PHP page. */
+								' ' . __( '<a href="%s">Learn more about updating PHP</a>.' ),
+								esc_url( wp_get_update_php_url() )
+							);
+							wp_update_php_annotation( '</p><p><em>', '</em>' );
+						}
+						?>
+					<# } #>
+				</p></div>
+			<# } #>
+
+			<# if ( data.theme.active ) { #>
+				<div class="theme-id-container">
+					<h3 class="theme-name" id="{{ data.section }}-{{ data.theme.id }}-name">
+						<span><?php _ex( 'Previewing:', 'theme' ); ?></span> {{ data.theme.name }}
+					</h3>
+					<div class="theme-actions">
+						<button type="button" class="button button-primary customize-theme" aria-label="<?php echo esc_attr( $customize_label ); ?>"><?php _e( 'Customize' ); ?></button>
+					</div>
+				</div>
+				<?php
+				wp_admin_notice(
+					_x( 'Installed', 'theme' ),
+					array(
+						'type'               => 'success',
+						'additional_classes' => array( 'notice-alt' ),
+					)
+				);
+				?>
+			<# } else if ( 'installed' === data.theme.type ) { #>
+				<# if ( data.theme.blockTheme ) { #>
+					<div class="theme-id-container">
+						<h3 class="theme-name" id="{{ data.section }}-{{ data.theme.id }}-name">{{ data.theme.name }}</h3>
+						<div class="theme-actions">
+							<# if ( data.theme.actions.activate ) { #>
+								<?php
+									/* translators: %s: Theme name. */
+									$aria_label = sprintf( _x( 'Activate %s', 'theme' ), '{{ data.name }}' );
+								?>
+								<a href="{{{ data.theme.actions.activate }}}" class="button button-primary activate" aria-label="<?php echo esc_attr( $aria_label ); ?>"><?php _e( 'Activate' ); ?></a>
+							<# } #>
+						</div>
+					</div>
+					<?php $customizer_not_supported_message = __( 'This theme doesn\'t support Customizer.' ); ?>
+					<# if ( data.theme.actions.activate ) { #>
+						<?php
+							$customizer_not_supported_message .= ' ' . sprintf(
+								/* translators: %s: URL to the themes page (also it activates the theme). */
+								__( 'However, you can still <a href="%s">activate this theme</a>, and use the Site Editor to customize it.' ),
+								'{{{ data.theme.actions.activate }}}'
+							);
+						?>
+					<# } #>
+
+					<?php
+					wp_admin_notice(
+						$customizer_not_supported_message,
+						array(
+							'type'               => 'error',
+							'additional_classes' => array( 'notice-alt' ),
+						)
+					);
+					?>
+				<# } else { #>
+					<div class="theme-id-container">
+						<h3 class="theme-name" id="{{ data.section }}-{{ data.theme.id }}-name">{{ data.theme.name }}</h3>
+						<div class="theme-actions">
+							<# if ( data.theme.compatibleWP && data.theme.compatiblePHP ) { #>
+								<button type="button" class="button button-primary preview-theme" aria-label="<?php echo esc_attr( $preview_label ); ?>" data-slug="{{ data.theme.id }}"><?php _e( 'Live Preview' ); ?></button>
+							<# } else { #>
+								<button type="button" class="button button-primary disabled" aria-label="<?php echo esc_attr( $preview_label ); ?>"><?php _e( 'Live Preview' ); ?></button>
+							<# } #>
+						</div>
+					</div>
+					<?php
+					wp_admin_notice(
+						_x( 'Installed', 'theme' ),
+						array(
+							'type'               => 'success',
+							'additional_classes' => array( 'notice-alt' ),
+						)
+					);
+					?>
+				<# } #>
+			<# } else { #>
+				<div class="theme-id-container">
+					<h3 class="theme-name" id="{{ data.section }}-{{ data.theme.id }}-name">{{ data.theme.name }}</h3>
+					<div class="theme-actions">
+						<# if ( data.theme.compatibleWP && data.theme.compatiblePHP ) { #>
+							<button type="button" class="button button-primary theme-install preview" aria-label="<?php echo esc_attr( $install_label ); ?>" data-slug="{{ data.theme.id }}" data-name="{{ data.theme.name }}"><?php _e( 'Install &amp; Preview' ); ?></button>
+						<# } else { #>
+							<button type="button" class="button button-primary disabled" aria-label="<?php echo esc_attr( $install_label ); ?>" disabled><?php _e( 'Install &amp; Preview' ); ?></button>
+						<# } #>
+					</div>
+				</div>
+			<# } #>
+		</div>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-themes-panel.php b/wp-includes/customize/class-wp-customize-themes-panel.php
new file mode 100644
index 0000000..42d475a
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-themes-panel.php
@@ -0,0 +1,114 @@
+<?php
+/**
+ * Customize API: WP_Customize_Themes_Panel class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.9.0
+ */
+
+/**
+ * Customize Themes Panel Class
+ *
+ * @since 4.9.0
+ *
+ * @see WP_Customize_Panel
+ */
+class WP_Customize_Themes_Panel extends WP_Customize_Panel {
+
+	/**
+	 * Panel type.
+	 *
+	 * @since 4.9.0
+	 * @var string
+	 */
+	public $type = 'themes';
+
+	/**
+	 * An Underscore (JS) template for rendering this panel's container.
+	 *
+	 * The themes panel renders a custom panel heading with the active theme and a switch themes button.
+	 *
+	 * @see WP_Customize_Panel::print_template()
+	 *
+	 * @since 4.9.0
+	 */
+	protected function render_template() {
+		?>
+		<li id="accordion-section-{{ data.id }}" class="accordion-section control-panel-themes">
+			<h3 class="accordion-section-title">
+				<?php
+				if ( $this->manager->is_theme_active() ) {
+					echo '<span class="customize-action">' . __( 'Active theme' ) . '</span> {{ data.title }}';
+				} else {
+					echo '<span class="customize-action">' . __( 'Previewing theme' ) . '</span> {{ data.title }}';
+				}
+				?>
+
+				<?php if ( current_user_can( 'switch_themes' ) ) : ?>
+					<button type="button" class="button change-theme" aria-label="<?php esc_attr_e( 'Change theme' ); ?>"><?php _ex( 'Change', 'theme' ); ?></button>
+				<?php endif; ?>
+			</h3>
+			<ul class="accordion-sub-container control-panel-content"></ul>
+		</li>
+		<?php
+	}
+
+	/**
+	 * An Underscore (JS) template for this panel's content (but not its container).
+	 *
+	 * Class variables for this panel class are available in the `data` JS object;
+	 * export custom variables by overriding WP_Customize_Panel::json().
+	 *
+	 * @since 4.9.0
+	 *
+	 * @see WP_Customize_Panel::print_template()
+	 */
+	protected function content_template() {
+		?>
+		<li class="panel-meta customize-info accordion-section <# if ( ! data.description ) { #> cannot-expand<# } #>">
+			<button class="customize-panel-back" tabindex="-1" type="button"><span class="screen-reader-text">
+				<?php
+				/* translators: Hidden accessibility text. */
+				_e( 'Back' );
+				?>
+			</span></button>
+			<div class="accordion-section-title">
+				<span class="preview-notice">
+					<?php
+					printf(
+						/* translators: %s: Themes panel title in the Customizer. */
+						__( 'You are browsing %s' ),
+						'<strong class="panel-title">' . __( 'Themes' ) . '</strong>'
+					); // Separate strings for consistency with other panels.
+					?>
+				</span>
+				<?php if ( current_user_can( 'install_themes' ) && ! is_multisite() ) : ?>
+					<# if ( data.description ) { #>
+						<button class="customize-help-toggle dashicons dashicons-editor-help" type="button" aria-expanded="false"><span class="screen-reader-text">
+							<?php
+							/* translators: Hidden accessibility text. */
+							_e( 'Help' );
+							?>
+						</span></button>
+					<# } #>
+				<?php endif; ?>
+			</div>
+			<?php if ( current_user_can( 'install_themes' ) && ! is_multisite() ) : ?>
+				<# if ( data.description ) { #>
+					<div class="description customize-panel-description">
+						{{{ data.description }}}
+					</div>
+				<# } #>
+			<?php endif; ?>
+
+			<div class="customize-control-notifications-container"></div>
+		</li>
+		<li class="customize-themes-full-container-container">
+			<div class="customize-themes-full-container">
+				<div class="customize-themes-notifications"></div>
+			</div>
+		</li>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-themes-section.php b/wp-includes/customize/class-wp-customize-themes-section.php
new file mode 100644
index 0000000..9d33a68
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-themes-section.php
@@ -0,0 +1,210 @@
+<?php
+/**
+ * Customize API: WP_Customize_Themes_Section class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Themes Section class.
+ *
+ * A UI container for theme controls, which are displayed within sections.
+ *
+ * @since 4.2.0
+ *
+ * @see WP_Customize_Section
+ */
+class WP_Customize_Themes_Section extends WP_Customize_Section {
+
+	/**
+	 * Section type.
+	 *
+	 * @since 4.2.0
+	 * @var string
+	 */
+	public $type = 'themes';
+
+	/**
+	 * Theme section action.
+	 *
+	 * Defines the type of themes to load (installed, wporg, etc.).
+	 *
+	 * @since 4.9.0
+	 * @var string
+	 */
+	public $action = '';
+
+	/**
+	 * Theme section filter type.
+	 *
+	 * Determines whether filters are applied to loaded (local) themes or by initiating a new remote query (remote).
+	 * When filtering is local, the initial themes query is not paginated by default.
+	 *
+	 * @since 4.9.0
+	 * @var string
+	 */
+	public $filter_type = 'local';
+
+	/**
+	 * Gets section parameters for JS.
+	 *
+	 * @since 4.9.0
+	 * @return array Exported parameters.
+	 */
+	public function json() {
+		$exported                = parent::json();
+		$exported['action']      = $this->action;
+		$exported['filter_type'] = $this->filter_type;
+
+		return $exported;
+	}
+
+	/**
+	 * Renders a themes section as a JS template.
+	 *
+	 * The template is only rendered by PHP once, so all actions are prepared at once on the server side.
+	 *
+	 * @since 4.9.0
+	 */
+	protected function render_template() {
+		?>
+		<li id="accordion-section-{{ data.id }}" class="theme-section">
+			<button type="button" class="customize-themes-section-title themes-section-{{ data.id }}">{{ data.title }}</button>
+			<?php if ( current_user_can( 'install_themes' ) || is_multisite() ) : // @todo Upload support. ?>
+			<?php endif; ?>
+			<div class="customize-themes-section themes-section-{{ data.id }} control-section-content themes-php">
+				<div class="theme-overlay" tabindex="0" role="dialog" aria-label="<?php esc_attr_e( 'Theme Details' ); ?>"></div>
+				<div class="theme-browser rendered">
+					<div class="customize-preview-header themes-filter-bar">
+						<?php $this->filter_bar_content_template(); ?>
+					</div>
+					<?php $this->filter_drawer_content_template(); ?>
+					<div class="error unexpected-error" style="display: none; ">
+						<p>
+							<?php
+							printf(
+								/* translators: %s: Support forums URL. */
+								__( 'An unexpected error occurred. Something may be wrong with WordPress.org or this server&#8217;s configuration. If you continue to have problems, please try the <a href="%s">support forums</a>.' ),
+								__( 'https://wordpress.org/support/forums/' )
+							);
+							?>
+						</p>
+					</div>
+					<ul class="themes">
+					</ul>
+					<p class="no-themes"><?php _e( 'No themes found. Try a different search.' ); ?></p>
+					<p class="no-themes-local">
+						<?php
+						printf(
+							/* translators: %s: "Search WordPress.org themes" button text. */
+							__( 'No themes found. Try a different search, or %s.' ),
+							sprintf( '<button type="button" class="button-link search-dotorg-themes">%s</button>', __( 'Search WordPress.org themes' ) )
+						);
+						?>
+					</p>
+					<p class="spinner"></p>
+				</div>
+			</div>
+		</li>
+		<?php
+	}
+
+	/**
+	 * Renders the filter bar portion of a themes section as a JS template.
+	 *
+	 * The template is only rendered by PHP once, so all actions are prepared at once on the server side.
+	 * The filter bar container is rendered by {@see render_template()}.
+	 *
+	 * @since 4.9.0
+	 */
+	protected function filter_bar_content_template() {
+		?>
+		<button type="button" class="button button-primary customize-section-back customize-themes-mobile-back"><?php _e( 'Go to theme sources' ); ?></button>
+		<# if ( 'wporg' === data.action ) { #>
+			<div class="search-form">
+				<label for="wp-filter-search-input-{{ data.id }}" class="screen-reader-text">
+					<?php
+					/* translators: Hidden accessibility text. */
+					_e( 'Search themes&hellip;' );
+					?>
+				</label>
+				<input type="search" id="wp-filter-search-input-{{ data.id }}" placeholder="<?php esc_attr_e( 'Search themes&hellip;' ); ?>" aria-describedby="{{ data.id }}-live-search-desc" class="wp-filter-search">
+				<div class="search-icon" aria-hidden="true"></div>
+				<span id="{{ data.id }}-live-search-desc" class="screen-reader-text">
+					<?php
+					/* translators: Hidden accessibility text. */
+					_e( 'The search results will be updated as you type.' );
+					?>
+				</span>
+			</div>
+			<button type="button" class="button feature-filter-toggle">
+				<span class="filter-count-0"><?php _e( 'Filter themes' ); ?></span><span class="filter-count-filters">
+					<?php
+					/* translators: %s: Number of filters selected. */
+					printf( __( 'Filter themes (%s)' ), '<span class="theme-filter-count">0</span>' );
+					?>
+				</span>
+			</button>
+		<# } else { #>
+			<div class="themes-filter-container">
+				<label for="{{ data.id }}-themes-filter" class="screen-reader-text">
+					<?php
+					/* translators: Hidden accessibility text. */
+					_e( 'Search themes&hellip;' );
+					?>
+				</label>
+				<input type="search" id="{{ data.id }}-themes-filter" placeholder="<?php esc_attr_e( 'Search themes&hellip;' ); ?>" aria-describedby="{{ data.id }}-live-search-desc" class="wp-filter-search wp-filter-search-themes" />
+				<div class="search-icon" aria-hidden="true"></div>
+				<span id="{{ data.id }}-live-search-desc" class="screen-reader-text">
+					<?php
+					/* translators: Hidden accessibility text. */
+					_e( 'The search results will be updated as you type.' );
+					?>
+				</span>
+			</div>
+		<# } #>
+		<div class="filter-themes-count">
+			<span class="themes-displayed">
+				<?php
+				/* translators: %s: Number of themes displayed. */
+				printf( __( '%s themes' ), '<span class="theme-count">0</span>' );
+				?>
+			</span>
+		</div>
+		<?php
+	}
+
+	/**
+	 * Renders the filter drawer portion of a themes section as a JS template.
+	 *
+	 * The filter bar container is rendered by {@see render_template()}.
+	 *
+	 * @since 4.9.0
+	 */
+	protected function filter_drawer_content_template() {
+		/*
+		 * @todo Use the .org API instead of the local core feature list.
+		 * The .org API is currently outdated and will be reconciled when the .org themes directory is next redesigned.
+		 */
+		$feature_list = get_theme_feature_list( false );
+		?>
+		<# if ( 'wporg' === data.action ) { #>
+			<div class="filter-drawer filter-details">
+				<?php foreach ( $feature_list as $feature_name => $features ) : ?>
+					<fieldset class="filter-group">
+						<legend><?php echo esc_html( $feature_name ); ?></legend>
+						<div class="filter-group-feature">
+							<?php foreach ( $features as $feature => $feature_name ) : ?>
+								<input type="checkbox" id="filter-id-<?php echo esc_attr( $feature ); ?>" value="<?php echo esc_attr( $feature ); ?>" />
+								<label for="filter-id-<?php echo esc_attr( $feature ); ?>"><?php echo esc_html( $feature_name ); ?></label>
+							<?php endforeach; ?>
+						</div>
+					</fieldset>
+				<?php endforeach; ?>
+			</div>
+		<# } #>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-customize-upload-control.php b/wp-includes/customize/class-wp-customize-upload-control.php
new file mode 100644
index 0000000..c992146
--- /dev/null
+++ b/wp-includes/customize/class-wp-customize-upload-control.php
@@ -0,0 +1,65 @@
+<?php
+/**
+ * Customize API: WP_Customize_Upload_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Customize Upload Control Class.
+ *
+ * @since 3.4.0
+ *
+ * @see WP_Customize_Media_Control
+ */
+class WP_Customize_Upload_Control extends WP_Customize_Media_Control {
+	/**
+	 * Control type.
+	 *
+	 * @since 3.4.0
+	 * @var string
+	 */
+	public $type = 'upload';
+
+	/**
+	 * Media control mime type.
+	 *
+	 * @since 4.1.0
+	 * @var string
+	 */
+	public $mime_type = '';
+
+	/**
+	 * Button labels.
+	 *
+	 * @since 4.1.0
+	 * @var array
+	 */
+	public $button_labels = array();
+
+	public $removed = '';         // Unused.
+	public $context;              // Unused.
+	public $extensions = array(); // Unused.
+
+	/**
+	 * Refresh the parameters passed to the JavaScript via JSON.
+	 *
+	 * @since 3.4.0
+	 *
+	 * @uses WP_Customize_Media_Control::to_json()
+	 */
+	public function to_json() {
+		parent::to_json();
+
+		$value = $this->value();
+		if ( $value ) {
+			// Get the attachment model for the existing file.
+			$attachment_id = attachment_url_to_postid( $value );
+			if ( $attachment_id ) {
+				$this->json['attachment'] = wp_prepare_attachment_for_js( $attachment_id );
+			}
+		}
+	}
+}
diff --git a/wp-includes/customize/class-wp-sidebar-block-editor-control.php b/wp-includes/customize/class-wp-sidebar-block-editor-control.php
new file mode 100644
index 0000000..a2d1e4b
--- /dev/null
+++ b/wp-includes/customize/class-wp-sidebar-block-editor-control.php
@@ -0,0 +1,37 @@
+<?php
+/**
+ * Customize API: WP_Sidebar_Block_Editor_Control class.
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 5.8.0
+ */
+
+/**
+ * Core class used to implement the widgets block editor control in the
+ * customizer.
+ *
+ * @since 5.8.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Sidebar_Block_Editor_Control extends WP_Customize_Control {
+	/**
+	 * The control type.
+	 *
+	 * @since 5.8.0
+	 *
+	 * @var string
+	 */
+	public $type = 'sidebar_block_editor';
+
+	/**
+	 * Render the widgets block editor container.
+	 *
+	 * @since 5.8.0
+	 */
+	public function render_content() {
+		// Render an empty control. The JavaScript in
+		// @wordpress/customize-widgets will do the rest.
+	}
+}
diff --git a/wp-includes/customize/class-wp-widget-area-customize-control.php b/wp-includes/customize/class-wp-widget-area-customize-control.php
new file mode 100644
index 0000000..6616282
--- /dev/null
+++ b/wp-includes/customize/class-wp-widget-area-customize-control.php
@@ -0,0 +1,71 @@
+<?php
+/**
+ * Customize API: WP_Widget_Area_Customize_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Widget Area Customize Control class.
+ *
+ * @since 3.9.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Widget_Area_Customize_Control extends WP_Customize_Control {
+
+	/**
+	 * Customize control type.
+	 *
+	 * @since 3.9.0
+	 * @var string
+	 */
+	public $type = 'sidebar_widgets';
+
+	/**
+	 * Sidebar ID.
+	 *
+	 * @since 3.9.0
+	 * @var int|string
+	 */
+	public $sidebar_id;
+
+	/**
+	 * Refreshes the parameters passed to the JavaScript via JSON.
+	 *
+	 * @since 3.9.0
+	 */
+	public function to_json() {
+		parent::to_json();
+		$exported_properties = array( 'sidebar_id' );
+		foreach ( $exported_properties as $key ) {
+			$this->json[ $key ] = $this->$key;
+		}
+	}
+
+	/**
+	 * Renders the control's content.
+	 *
+	 * @since 3.9.0
+	 */
+	public function render_content() {
+		$id = 'reorder-widgets-desc-' . str_replace( array( '[', ']' ), array( '-', '' ), $this->id );
+		?>
+		<button type="button" class="button add-new-widget" aria-expanded="false" aria-controls="available-widgets">
+			<?php _e( 'Add a Widget' ); ?>
+		</button>
+		<button type="button" class="button-link reorder-toggle" aria-label="<?php esc_attr_e( 'Reorder widgets' ); ?>" aria-describedby="<?php echo esc_attr( $id ); ?>">
+			<span class="reorder"><?php _e( 'Reorder' ); ?></span>
+			<span class="reorder-done"><?php _e( 'Done' ); ?></span>
+		</button>
+		<p class="screen-reader-text" id="<?php echo esc_attr( $id ); ?>">
+			<?php
+			/* translators: Hidden accessibility text. */
+			_e( 'When in reorder mode, additional controls to reorder widgets will be available in the widgets list above.' );
+			?>
+		</p>
+		<?php
+	}
+}
diff --git a/wp-includes/customize/class-wp-widget-form-customize-control.php b/wp-includes/customize/class-wp-widget-form-customize-control.php
new file mode 100644
index 0000000..cfab188
--- /dev/null
+++ b/wp-includes/customize/class-wp-widget-form-customize-control.php
@@ -0,0 +1,140 @@
+<?php
+/**
+ * Customize API: WP_Widget_Form_Customize_Control class
+ *
+ * @package WordPress
+ * @subpackage Customize
+ * @since 4.4.0
+ */
+
+/**
+ * Widget Form Customize Control class.
+ *
+ * @since 3.9.0
+ *
+ * @see WP_Customize_Control
+ */
+class WP_Widget_Form_Customize_Control extends WP_Customize_Control {
+	/**
+	 * Customize control type.
+	 *
+	 * @since 3.9.0
+	 * @var string
+	 */
+	public $type = 'widget_form';
+
+	/**
+	 * Widget ID.
+	 *
+	 * @since 3.9.0
+	 * @var string
+	 */
+	public $widget_id;
+
+	/**
+	 * Widget ID base.
+	 *
+	 * @since 3.9.0
+	 * @var string
+	 */
+	public $widget_id_base;
+
+	/**
+	 * Sidebar ID.
+	 *
+	 * @since 3.9.0
+	 * @var string
+	 */
+	public $sidebar_id;
+
+	/**
+	 * Widget status.
+	 *
+	 * @since 3.9.0
+	 * @var bool True if new, false otherwise. Default false.
+	 */
+	public $is_new = false;
+
+	/**
+	 * Widget width.
+	 *
+	 * @since 3.9.0
+	 * @var int
+	 */
+	public $width;
+
+	/**
+	 * Widget height.
+	 *
+	 * @since 3.9.0
+	 * @var int
+	 */
+	public $height;
+
+	/**
+	 * Widget mode.
+	 *
+	 * @since 3.9.0
+	 * @var bool True if wide, false otherwise. Default false.
+	 */
+	public $is_wide = false;
+
+	/**
+	 * Gather control params for exporting to JavaScript.
+	 *
+	 * @since 3.9.0
+	 *
+	 * @global array $wp_registered_widgets
+	 */
+	public function to_json() {
+		global $wp_registered_widgets;
+
+		parent::to_json();
+		$exported_properties = array( 'widget_id', 'widget_id_base', 'sidebar_id', 'width', 'height', 'is_wide' );
+		foreach ( $exported_properties as $key ) {
+			$this->json[ $key ] = $this->$key;
+		}
+
+		// Get the widget_control and widget_content.
+		require_once ABSPATH . 'wp-admin/includes/widgets.php';
+
+		$widget = $wp_registered_widgets[ $this->widget_id ];
+		if ( ! isset( $widget['params'][0] ) ) {
+			$widget['params'][0] = array();
+		}
+
+		$args = array(
+			'widget_id'   => $widget['id'],
+			'widget_name' => $widget['name'],
+		);
+
+		$args                 = wp_list_widget_controls_dynamic_sidebar(
+			array(
+				0 => $args,
+				1 => $widget['params'][0],
+			)
+		);
+		$widget_control_parts = $this->manager->widgets->get_widget_control_parts( $args );
+
+		$this->json['widget_control'] = $widget_control_parts['control'];
+		$this->json['widget_content'] = $widget_control_parts['content'];
+	}
+
+	/**
+	 * Override render_content to be no-op since content is exported via to_json for deferred embedding.
+	 *
+	 * @since 3.9.0
+	 */
+	public function render_content() {}
+
+	/**
+	 * Whether the current widget is rendered on the page.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @return bool Whether the widget is rendered.
+	 */
+	public function active_callback() {
+		return $this->manager->widgets->is_widget_rendered( $this->widget_id );
+	}
+}