function is_set_to_default($index = NULL)
 {
     // special case, compare value arrays against blank default
     if (is_array($this->value) && $this->default == '') {
         foreach ($this->value as $value) {
             if ($value != '') {
                 return FALSE;
             }
         }
         return TRUE;
     }
     return parent::is_set_to_default($index);
 }