protected function createTransactionNode()
    {
        $xml = new DOMDocument();
        $xml->formatOutput = true;

        $trxRef = $xml->appendChild($xml->createElement('TransactionReference'));

        if (null !== $this->context) {
            $trxRef->appendChild($xml->createElement('CustomerContext', $this->context));
        }

        return $trxRef->cloneNode(true);
    }