code: function DOMWalker_getNode(idSet) {
      var doc = this._controller.window.document;
  
      // QuerySelector seems to be unusuale for id's in this case:
      // https://developer.mozilla.org/En/Code_snippets/QuerySelector
      switch (idSet.getBy) {
        case DOMWalker.GET_BY_ID:
          return doc.getElementById(idSet[idSet.getBy]);
        case DOMWalker.GET_BY_SELECTOR:
          return doc.querySelector(idSet[idSet.getBy]);
        default:
          throw new Error("Not supported getBy-attribute: " + idSet.getBy);
      }
    }
docs: Retrieves and returns a wanted node based on the provided identification
  set.
  
  @param {array of objects} idSet
  Contains informations on the elements to open while
  Object-elements:  getBy         - attribute-name of the attribute
  containing the identification
  information for the opener-element
  subContent    - array of ids of the opener-elements
  in the window with the value of
  the above getBy-attribute
  target        - information, where the new
  elements will be opened
  [1|2|4]
  title         - title of the opened dialog/window
  waitFunction  - The function used as an argument
  for MozmillController.waitFor to
  wait before starting the walk.
  [optional - default: no waiting]
  windowHandler - Window instance
  [only needed for some tests]
  
  @returns Node
  @type {Node}