A code which identifies a group of positionally disordered atom sites that are locally simultaneously occupied. Atoms that are positionally disordered over two or more sites (e.g. the hydrogen atoms of a methyl group that exists in two orientations) can be assigned to two or more groups. Sites belonging to the same group are simultaneously occupied, but those belonging to different groups are not. A minus prefix (e.g. '-1') is used to indicate sites disordered about a special position. *** This data item would not in general be used in a macromolecular data block. ***