Builder: CIF partial occupancies are reported, and an ordered supercell can be chosen #595

NBOMAT, via Andy 10-26 (SOMS, Na3 at occupancy 0.5, ICSD 55415). With CIF import (#358): report sites with occupancy < 1 instead of silently placing every site as fully occupied; offer to build a supercell and pick one ordered arrangement (or refuse the import with the list of partial sites).