code: def add_parameters(self, **params):
          
          self.url_params = None
          # we want JSON by default
          if not params.get("format"):
              params["format"] = "json"
          # non-standard content must be retrieved as Atom
          if params.get("content"):
              params["format"] = "atom"
          # TODO: rewrite format=atom, content=json request
          if "limit" not in params or params.get("limit") == 0:
              params["limit"] = 100
          # Need ability to request arbitrary number of results for version
          # response
          # -1 value is hack that works with current version
          elif params["limit"] == -1 or params["limit"] is None:
              del params["limit"]
          # bib format can't have a limit
          if params.get("format") == "bib":
              del params["limit"]
          self.url_params = urlencode(params, doseq=True)
docs: Add URL parameters
          Also ensure that only valid format/content combinations are requested