Please tell my what is 10, 2 in below mention code:
add_filter('nav_menu_css_class', 'add_active_class', 10, 2 );
function add_active_class($classes, $item) {
if($item->menu_item_parent == 0 && in_array('current-menu-item', $classes)) {
$classes[] = "active";
}
return $classes;
}