code: def validated_formatter(self, url_format):
      
      # We try to create a string by substituting all known
      # parameters. If an unknown parameter is present, an error
      # will be thrown
      valid_parameters = {
          "${CLUSTER}": "cluster",
          "${ENVIRON}": "environ",
          "${TOPOLOGY}": "topology",
          "${ROLE}": "role",
          "${USER}": "user",
      }
      dummy_formatted_url = url_format
      for key, value in valid_parameters.items():
        dummy_formatted_url = dummy_formatted_url.replace(key, value)
  
      # All $ signs must have been replaced
      if '$' in dummy_formatted_url:
        raise Exception("Invalid viz.url.format: %s" % (url_format))
  
      # No error is thrown, so the format is valid.
      return url_format
docs: validate visualization url format