              The descriptor that categorizes type of the conformation of the\
               backbone of the polymer (whether protein or nucleic acid).\
               Explicit values for the torsions angles that define each\
               conformation are not given here, but it is expected that the\
               author would provide such information in either the\
               _struct_conf_type.criteria or _struct_conf_type.reference data\
               items, or both.