Contains all the data items that refer to the space group as a
               whole, such as its name or crystal system. They may be looped,
               for example, in a list of space groups and their properties.

               Only a subset of the SPACE_GROUP category items appear in
               this dictionary.  The remainder are found in the symmetry CIF
               dictionary.

               Space-group types are identified by their number as given in
               International Tables for Crystallography Vol. A. Specific
               settings of the space groups can be identified either by their
               Hall symbol or by specifying their symmetry operations.

               The commonly used Hermann-Mauguin symbol determines the
               space-group type uniquely but several different Hermann-Mauguin
               symbols may refer to the same space-group type. A Hermann-Mauguin
               symbol contains information on the choice of the basis, but not
               on the choice of origin.  Different formats for the
               Hermann-Mauguin symbol are found in the symmetry CIF dictionary.