docs: def format(self, status, headers, environ, bucket, delay):
          """
          Formats a response entity.  Returns a tuple of the desired
          status code and the formatted entity.  The default status code
          is passed in, as is a dictionary of headers.
  
          :param status: The default status code.  Should be returned to
                         the caller, or an alternate selected.  The
                         status code should include both the number and
                         the message, separated by a single space.
          :param headers: A dictionary of headers for the response.
                          Should update the 'Content-Type' header at a
                          minimum.
          :param environ: The WSGI environment for the request.
          :param bucket: The bucket containing the data which caused the
                         delay decision to be made.  This can be used to
                         obtain such information as the next time the
                         request can be made.
          :param delay: The number of seconds by which the request
                        should be delayed.
          """
  
          # This is a default response entity, which can be overridden
          # by limit subclasses.
          entity = ("This request was rate-limited.  "
                    "Please retry your request after %s." %
                    time.strftime("%Y-%m-%dT%H:%M:%SZ",
                                  time.gmtime(bucket.next)))
          headers['Content-Type'] = 'text/plain'
  
          return status, entity