docs: def contains(self, chrom, start, end, overlap=True):
          """This returns a list of VCFEntry objects which cover a specified location.
  
          :param chrom: 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 VCFEntry object
          spanning from (8,15). overlap=False will only return objects fully containing the range.
          :return: A list of VCFEntry objects
          """
          d = self.positions.get(chrom,[])
          if overlap:
              return [vcf_entry for vcf_start, vcf_end in d
                      for vcf_entry in d[(vcf_start, vcf_end)]
                      if not (end < vcf_start or start > vcf_end)]
          else:
              return [vcf_entry for vcf_start, vcf_end in d
                      for vcf_entry in d[(vcf_start, vcf_end)]
                      if (vcf_start <= start and vcf_end >= end)]