wp_dropdown_categories and custom attribute
The only filter available is wp_dropdown_cats, which allows you to filter the entire HTML select string and that means trying to string-match markup. That is always a bit questionable. Still… function dropdown_data_attr_wpse_213033($output){ return str_replace(‘<select’,'<select data-live-search=”true”‘,$output); } add_filter(‘wp_dropdown_cats’,’dropdown_data_attr_wpse_213033′); wp_dropdown_categories(); // test