public function toXml()
    {
        $this->parse();
        $doc = new DomDocument('1.0', 'utf-8');
        $optionsNode = $doc->createElement('options');
        $doc->appendChild($optionsNode);
        foreach ($this->_options as $flag => $value) {
            $optionNode = $doc->createElement('option');
            $optionNode->setAttribute('flag', utf8_encode($flag));
            if ($value !== true) {
                $optionNode->setAttribute('parameter', utf8_encode($value));
            }
            $optionsNode->appendChild($optionNode);
        }
        $xml = $doc->saveXML();
        return $xml;
    }