code: def is_deletion(self):
          
          # A deletion would appear in a VCF like CT>C, so that the
          # reference allele starts with the alternate nucleotides.
          # This is true even in the normalized case, where the alternate
          # nucleotides are an empty string.
          return (len(self.ref) > len(self.alt)) and self.ref.startswith(self.alt)
docs: Does this variant represent the deletion of nucleotides from the
          reference genome?