              Data items in the STRUCT_REF category allow the author of a\
               data block to relate the entities or biological units\
               described in that data block to information archived in external\
               databases.\
\
               For references to the sequence of a polymer, the value of\
               the data item _struct_ref.seq_align is used to indicate\
               whether the correspondence between the sequence of the entity\
               or biological unit in the data block and the sequence in the\
               referenced database entry is 'complete' or 'partial'. If\
               this value is 'partial', the region (or regions) of the\
               alignment may be delimited using data items in the\
               STRUCT_REF_SEQ category.\
\
               Also for references to the sequence of a polymer, the value of\
               _struct_ref.seq_dif is used to indicate whether or not the\
               two sequences contain point differences. If the value is yes,\
               the differences may be identified and annotated using data\
               items in the STRUCT_REF_SEQ_DIF category.