*
* @param string $output Passed by reference. Used to append additional content.
* @param object $category Category data object.
* @param int $depth Depth of category. Used for padding.
* @param array $args Uses 'selected', 'show_count', and 'value_field' keys, if they exist.
*
* @param string $output Passed by reference. Used to append additional content.
* @param object $category Category data object.
* @param int $depth Depth of category. Used for padding.
* @param array $args Uses 'selected', 'show_count', and 'value_field' keys, if they exist.