docs: def _create_request_schema(self, params, required):
          """Create a JSON schema for a request.
  
          :param list params: A list of keys specifying which definitions from
              the base schema should be allowed in the request.
          :param list required: A subset of the params that the requester must
              specify in the request.
          :returns: a JSON schema dict
          """
          # We allow additional properties because the data this will validate
          # may also include kwargs passed by decorators on the handler method.
          schema = {'additionalProperties': True,
                    'definitions': self.resolve('#/definitions'),
                    'properties': {},
                    'required': required or (),
                    'type': 'object'}
          for param in params:
              schema['properties'][param] = {
                  '$ref': '#/definitions/{}'.format(param)}
          return schema