Problem with DOLFIN XML data

The format can be xml or xdmf. XDMF is preferrable, as it is more suitable for parallel computations.
See for instance: What is wrong with my mesh? - #8 by dokken
where you would have to change cell_data = mesh.get_cell_data("gmsh:physical", cell_type)
to get the tag from the file read in with meshio.