public function appendList(array $data, $elementName, $nsPrefix = null, $nsUri = null)
    {
        if (null === $nsPrefix) {
            foreach ($data as $value) {
                $this->writeElement($elementName, $value);
            }
        } else {
            foreach ($data as $value) {
                $this->writeElementNS($nsPrefix, $elementName, $nsUri, $value);
            }
        }

        return true;
    }