WP_Customize_Nav_Menu_Setting::preview(): bool

205	public function preview() {206		if ( $this->is_previewed ) {207			return false;208		}209 210		$undefined      = new stdClass();211		$is_placeholder = ( $this->term_id < 0 );212		$is_dirty       = ( $undefined !== $this->post_value( $undefined ) );213		if ( ! $is_placeholder && ! $is_dirty ) {214			return false;215		}216 217		$this->is_previewed       = true;218		$this->_original_value    = $this->value();219		$this->_previewed_blog_id = get_current_blog_id();220 221		add_filter( 'wp_get_nav_menus', array( $this, 'filter_wp_get_nav_menus' ), 10, 2 );222		add_filter( 'wp_get_nav_menu_object', array( $this, 'filter_wp_get_nav_menu_object' ), 10, 2 );223		add_filter( 'default_option_nav_menu_options', array( $this, 'filter_nav_menu_options' ) );224		add_filter( 'option_nav_menu_options', array( $this, 'filter_nav_menu_options' ) );225 226		return true;227	}