Nette\Forms\Rules::validateRule PHP Method

    public static function validateRule(Rule $rule)
    {
        $args = is_array($rule->arg) ? $rule->arg : [$rule->arg];
        foreach ($args as &$val) {
            $val = $val instanceof IControl ? $val->getValue() : $val;
        }
        return $rule->isNegative xor call_user_func(self::getCallback($rule), $rule->control, is_array($rule->arg) ? $args : $args[0]);
    }