static parseXmlString(xmlString, expectedRootElemName,
      includeParent = false) {
    const result = shaka.util.TXml.parse(xmlString, includeParent);
    if (!expectedRootElemName && result.length) {
      return result[0];
    }
    const rootNode = result.find((n) =>
      expectedRootElemName.split(',').includes(n.tagName));
    if (rootNode) {
      return rootNode;
    }

    shaka.log.error('parseXml root element not found!');
    return null;
  }
Parse some data
@param {string} xmlString
@param {string=} expectedRootElemName
@param {boolean=} includeParent
@return {shaka.extern.xml.Node | null}