If set to True, then all non-water 'HETATM' records are read from PDB, mmCIF or BinaryCIF files. (By default, only 'ATOM' records are read. To read waters, use IOData.water.) Note that you will usually need to turn this on when using BLK residues, or if you want to use a PDB, mmCIF, or BinaryCIF file containing ligands.