code: function aboutSessionRestore_getElement(spec) {
      var elem = null;
  
      switch(spec.type) {
        case "button_restoreSession":
          elem = new elementslib.ID(this._controller.tabs.activeTab, "errorTryAgain");
          break;
        case "error_longDesc":
          elem = new elementslib.ID(this._controller.tabs.activeTab, "errorLongDesc");
          break;
        case "error_pageContainer":
          elem = new elementslib.ID(this._controller.tabs.activeTab, "errorPageContainer");
          break;
        case "error_shortDesc":
          elem = new elementslib.ID(this._controller.tabs.activeTab, "errorShortDescText");
          break;
        case "error_title":
          elem = new elementslib.ID(this._controller.tabs.activeTab, "errorTitleText");
          break;
        case "tabList":
          elem = new elementslib.ID(this._controller.window.document, "tabList");
          break;
        default:
          throw new Error(arguments.callee.name + ": Unknown element type - " + spec.type);
      }
  
      return elem;
    }
docs: Retrieve an UI element based on the given spec
  
  @param {object} spec
  Information of the UI element which should be retrieved
  type: General type information
  subtype: Specific element or property
  value: Value of the element or property
  @returns Element which has been created
  @type {ElemBase}