docs: def load_transaction_config(self, file_id):
          """
          Loads the configuration fields file for the id.
  
          :param file_id: the id for the field
          :return: the fields configuration
          """
          if file_id not in self._transaction_configs:
              self._transaction_configs[file_id] = self._reader.read_config_file(
                  'transaction_config_%s.cml' % file_id)
  
          return self._transaction_configs[file_id]