docs: function getIdxOfMatchingSelector(tNode, selector) {
      var localNames = tNode.localNames;
      if (localNames) {
          for (var i = 0; i < localNames.length; i += 2) {
              if (localNames[i] === selector) {
                  return localNames[i + 1];
              }
          }
      }
      return null;
  }