docs: def rate_limit_ensembl_requests(self):
          """ limit ensembl requests to one per 0.067 s
          """
          
          current_time = time.time()
          diff_time = current_time - self.prior_time
          
          # sleep until the current rate limit period is finished
          if diff_time < self.rate_limit:
              time.sleep(self.rate_limit - diff_time)
          
          # set the access time to now, for later checks
          self.prior_time = time.time()