docs: def setHorizontalAxis(self, axis):
          """
          Sets the horizontal axis for this chart.
          
          :param      axis | <XChartAxis>
          """
          self._horizontalAxis = axis
          if axis:
              axis.setOrientation(Qt.Horizontal)
              self.uiXAxisVIEW.setFixedHeight(axis.minimumLabelHeight() + 5)
          
          self.uiXAxisVIEW.setVisible(axis is not None)