docs: function (axisDimName, axisIndex) {
          if (axisDimName == null && axisIndex == null) {
              var axisProxy = this.findRepresentativeAxisProxy();
              if (axisProxy) {
                  return axisProxy.getDataValueWindow();
              }
          }
          else {
              return this.getAxisProxy(axisDimName, axisIndex).getDataValueWindow();
          }
      }