It would be useful to add the data item _entity_poly_seq_dif.db_seq_num to ENTITY_POLY_SEQ_DIF with the description "The sequence number for this position as given in the database entry indicated by _entity_poly_seq_dif.db_code and _entity_poly_seq_dif.db_name." This would make it simpler to unambiguously specify a sequence alignment (or misalignment). It would also be helpful to add _entity_poly_seq_dif.details to the category key to simplify specifying multiple interesting differences at the same point (e.g. both an alignment and a mutation).