code: def slug(self):
          
          return '{:s}@{:s}[{:d}, {:d}]'.format(self.type, self.seqid,
                                                self.start + 1, self.end)
docs: A concise slug for this feature.
  
          Unlike the internal representation, which is 0-based half-open, the
          slug is a 1-based closed interval (a la GFF3).