Nette\Forms\Controls\BaseControl::validate PHP Method

    public function validate()
    {
        if ($this->isDisabled()) {
            return;
        }
        $this->cleanErrors();
        $this->rules->validate();
    }

 /**
  * Performs the server side validation.
  * @return void
  */
 public function validate()
 {
     parent::validate();
     if (!$this->isDisabled() && $this->prompt === FALSE && $this->getValue() === NULL) {
         $this->addError(Nette\Forms\Validator::$messages[self::VALID]);
     }
 }