static function add_subpage(
			$parent_slug,
			$page_title,
			$menu_title,
			$capability,
			$menu_slug,
			$function = ''
		) {
			$fn = 'add_submenu' . '_page';

			return $fn( $parent_slug,
				$page_title,
				$menu_title,
				$capability,
				$menu_slug,
				$function
			);
		}