code: def _get_plane_axes_index(self, axis):
          
          axis_name = self._get_axis_name(axis)
  
          if axis_name == 'major_axis':
              index = 'minor_axis'
              columns = 'items'
          if axis_name == 'minor_axis':
              index = 'major_axis'
              columns = 'items'
          elif axis_name == 'items':
              index = 'major_axis'
              columns = 'minor_axis'
  
          return index, columns
docs: Get my plane axes indexes: these are already
          (as compared with higher level planes),
          as we are returning a DataFrame axes indexes.