code: function (index) {
                      /// <signature helpKeyword="WinJS.Binding.ListBase.getAt">
                      /// <summary locid="WinJS.Binding.ListBase.getAt">
                      /// Gets the value at the specified index.
                      /// </summary>
                      /// <param name="index" type="Number" integer="true" locid="WinJS.Binding.ListBase.getAt_p:index">The index of the value to get.</param>
                      /// <returns type="Object" mayBeNull="true" locid="WinJS.Binding.ListBase.getAt_returnValue">The value at the specified index.</returns>
                      /// </signature>
                      index = asNumber(index);
                      var item = this.getItem(index);
                      return item && item.data;
                  }
docs: NOTE: performance can be improved in a number of the projections by overriding getAt/_getArray/_getFromKey/_getKey