docs: def region(self, start=0, end=None):
          '''
          Returns a region of ``Sequence.sequence``, in FASTA format.
  
          If called without kwargs, the entire sequence will be returned.
  
          Args:
  
              start (int): Start position of the region to be returned. Default
                  is 0.
  
              end (int): End position of the region to be returned. Negative values
                  will function as they do when slicing strings.
  
          Returns:
  
              str: A region of ``Sequence.sequence``, in FASTA format
          '''
          if end is None:
              end = len(self.sequence)
          return '>{}\n{}'.format(self.id, self.sequence[start:end])