Nette\Forms\Controls\BaseControl::isRequired PHP Метод

    public function isRequired()
    {
        return $this->rules->isRequired();
    }

 public static function label(Html $label, BaseControl $control, $isPart)
 {
     if ($label->getName() === 'label') {
         $label->addClass('control-label');
     }
     if ($control->isRequired()) {
         $label->addClass('required');
     }
     return $label;
 }