Walker_Nav_Menu::start_lvl()
Method: Starts the list before the elements are added.
Source: wp-includes/class-walker-nav-menu.php:70
nav_menu_submenu_css_class
Filter Hook: Filters the CSS class(es) applied to a menu list element.
Source: wp-includes/class-walker-nav-menu.php:92
Walker_Nav_Menu::end_lvl()
Method: Ends the list of after the elements are added.
Source: wp-includes/class-walker-nav-menu.php:109