docs: def get_content_descendants_by_type(self, content_id, child_type, expand=None, start=None, limit=None,
                                          callback=None):
          """
          Returns the direct descendants of a piece of Content, limited to a single descendant type.
  
          The {@link ContentType}(s) of the descendants returned is specified by the "type" path parameter in the request.
  
          Currently the only supported descendants are comment descendants of non-comment Content.
          :param content_id (string): A string containing the id of the content to retrieve descendants for
          :param child_type (string): A {@link ContentType} to filter descendants on.
          :param expand (string): OPTIONAL: A comma separated list of properties to expand on the descendants.
                                  Default: Empty
          :param start (int): OPTIONAL: The index of the first item within the result set that should be returned.
                              Default: 0.
          :param limit (int): OPTIONAL: How many items should be returned after the start index.
                              Default: 25 or site limit.
          :param callback: OPTIONAL: The callback to execute on the resulting data, before the method returns.
                           Default: None (no callback, raw data returned).
          :return: The JSON data returned from the content/{id}/descendant/{type} endpoint, or the results of the
                   callback. Will raise requests.HTTPError on bad input, potentially.
          """
          params = {}
          if expand:
              params["expand"] = expand
          if start is not None:
              params["start"] = int(start)
          if limit is not None:
              params["limit"] = int(limit)
          return self._service_get_request("rest/api/content/{id}/descendant/{type}"
                                           "".format(id=content_id, type=child_type), params=params, callback=callback)