Nette\Forms\Rules::getCallback PHP Method

    private static function getCallback($rule)
    {
        $op = $rule->validator;
        if (is_string($op) && strncmp($op, ':', 1) === 0) {
            return 'Nette\\Forms\\Validator::validate' . ltrim($op, ':');
        } else {
            return $op;
        }
    }