public function writeInnerXml(\XMLWriter $xmlWriter)
    {
        Validate::notNull($xmlWriter, 'xmlWriter');
        $this->writeOptionalAttribute(
            $xmlWriter,
            'term',
            $this->term
        );

        $this->writeOptionalAttribute(
            $xmlWriter,
            'scheme',
            $this->scheme
        );

        $this->writeOptionalAttribute(
            $xmlWriter,
            'label',
            $this->label
        );

        if (!empty($this->undefinedContent)) {
            $xmlWriter->writeRaw($this->undefinedContent);
        }
    }