Load a :code:`##sequence-region` directive into memory.

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()