code: def convert_contentbody_to_new_type(self, content_data, old_representation, new_representation, callback=None):
          
          assert {old_representation, new_representation} < {"storage", "editor", "view", "export_view"}
          # TODO: Enforce conversion rules better here.
          request_data = {"value": str(content_data), "representation": old_representation}
          return self._service_post_request("rest/api/contentbody/convert/{to}".format(to=new_representation),
                                            data=json.dumps(request_data),
                                            headers={"Content-Type": "application/json"}, callback=callback)
docs: Converts between content body representations.
  
          Not all representations can be converted to/from other formats. Supported conversions:
  
          Source Representation |   Destination Representation Supported
          --------------------------------------------------------------
          "storage"               |   "view","export_view","editor"
          "editor"                |   "storage"
          "view"                  |   None
          "export_view"           |   None
  
          :param content_data (string): The content data to transform.
          :param old_representation (string): The representation to convert from.
          :param new_representation (string): The representation to convert to.
          :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 contentbody/convert/{to} endpoint,
                   or the results of the callback. Will raise requests.HTTPError on bad input, potentially.