public function validate($val)
 {
     if ($this->required) {
         if (Useful::stripper($val) === false) {
             $this->error[] = 'is required';
         }
     }
     if (in_array($val, $this->false_values)) {
         $this->error[] = 'is not a valid selection';
     }
     return !empty($this->error) ? false : true;
 }