code: function _parseXml( xmlStr ) {
      let doc;
  
      return new Promise( ( resolve, reject ) => {
          try {
              doc = libxmljs.parseXml( xmlStr );
              resolve( doc );
          } catch ( e ) {
              reject( e );
          }
      } );
  }
docs: Parses and XML string into a libxmljs object
  
  @param  {string} xmlStr XML string
  @return {Promise}       libxmljs result document object