apply_filters( 'nav_menu_submenu_css_class', string[] $classes, stdClass $args, int $depth )

86		 * @since 4.8.087		 *88		 * @param string[] $classes Array of the CSS classes that are applied to the menu `<ul>` element.89		 * @param stdClass $args    An object of `wp_nav_menu()` arguments.90		 * @param int      $depth   Depth of menu item. Used for padding.91		 */92		$class_names = implode( ' ', apply_filters( 'nav_menu_submenu_css_class', $classes, $args, $depth ) );93 94		$atts          = array();95		$atts['class'] = ! empty( $class_names ) ? $class_names : '';96 97		/**98		 * Filters the HTML attributes applied to a menu list element.