public function clean_values()
 {
     parent::clean_values();
     if (!empty($this->final_elements)) {
         foreach ($this->final_elements as $final_element) {
             $final_element->clean_values();
         }
     }
     if (!empty($this->children)) {
         foreach ($this->children as $child) {
             $child->clean_values();
         }
     }
     if (!empty($this->optigroup)) {
         $this->optigroup->clean_values();
     }
 }