public function isValid($value)
    {
        $emails = explode(((false !== strpos($value, ',')) ? ',' : ';'), $value);
        //iteracja po mailach
        foreach ($emails as $email) {
            //niepoprawny email
            if (!(new EmailAddress)->isValid($email)) {
                return $this->_error(self::INVALID);
            }
        }
        return true;
    }