docs: def _check_triangular_bounds(self, var, coords=None, axis='x', nans=None):
          """
          Checks whether the bounds in the variable attribute are triangular
  
          Parameters
          ----------
          %(CFDecoder.get_cell_node_coord.parameters)s
  
          Returns
          -------
          bool or None
              True, if unstructered, None if it could not be determined
          xarray.Coordinate or None
              the bounds corrdinate (if existent)"""
          # !!! WILL BE REMOVED IN THE NEAR FUTURE! !!!
          bounds = self.get_cell_node_coord(var, coords, axis=axis,
                                                nans=nans)
          if bounds is not None:
              return bounds.shape[-1] == 3, bounds
          else:
              return None, None