docs: def contains(self, seqid, start, end, overlap=True):
          """This returns a list of GFF objects which cover a specified location.
  
          :param seqid: The landmark identifier (usually a chromosome)
          :param start: The 1-based position of the start of the range we are querying
          :param end: The 1-based position of the end of the range we are querying
          :param overlap: A boolean value, if true we allow features to overlap the query range.
          For instance, overlap=True with the range (5,10), will return a GFF object
          spanning from (8,15). overlap=False will only return objects fully containing the range.
          :return: A list of GFF objects
          """
          d = self.positions.get(seqid,[])
          if overlap:
              return [gff_object for gff_start, gff_end in d
                      for gff_object in d[(gff_start, gff_end)]
                      if not (end <= gff_start or start >= gff_end)]
          else:
              return [gff_object for gff_start, gff_end in d
                      for gff_object in d[(gff_start, gff_end)]
                      if (gff_start <= start and gff_end >= end)]