docs: def get_zname(self, var, coords=None):
          """Get the name of the z-dimension
  
          This method gives the name of the z-dimension (which is not necessarily
          the name of the coordinate if the variable has a coordinate attribute)
  
          Parameters
          ----------
          var: xarray.Variables
              The variable to get the dimension for
          coords: dict
              The coordinates to use for checking the axis attribute. If None,
              they are not used
  
          Returns
          -------
          str or None
              The coordinate name or None if no vertical coordinate could be
              found
  
          See Also
          --------
          get_z"""
          if coords is not None:
              coord = self.get_variable_by_axis(var, 'z', coords)
              if coord is not None and coord.name in var.dims:
                  return coord.name
          dimlist = list(self.z.intersection(var.dims))
          if dimlist:
              if len(dimlist) > 1:
                  warn("Found multiple matches for z coordinate in the variable:"
                       "%s. I use %s" % (', '.join(dimlist), dimlist[0]),
                       PsyPlotRuntimeWarning)
              return dimlist[0]
          # otherwise we return the coordinate in the third last position
          is_unstructured = self.is_unstructured(var)
          icheck = -2 if is_unstructured else -3
          min_dim = abs(icheck) if 'variable' not in var.dims else abs(icheck-1)
          if var.ndim >= min_dim and var.dims[icheck] != self.get_tname(
                  var, coords):
              return var.dims[icheck]
          return None