docs: def consume_seqreg(self, seqreg):
          """Load a :code:`##sequence-region` directive into memory."""
          if not isinstance(seqreg, tag.directive.Directive) or \
                  seqreg.type != 'sequence-region':
              raise ValueError('expected ##sequence-region directive')
          if seqreg.seqid in self.declared_regions:
              msg = 'duplicate sequence region "{}"'.format(seqreg.seqid)
              raise ValueError(msg)
          self.declared_regions[seqreg.seqid] = seqreg.range.copy()