docs: def encode(self, transmission):
          """
          Encodes the data, creating a CWR structure from an instance from the
          domain model.
  
          :param entity: the instance to encode
          :return: a cwr string structure created from the received data
          """
          data = ''
          data += self._record_encode(transmission.header)
          for group in transmission.groups:
              data += self._record_encode(group.group_header)
              for transaction in group.transactions:
                  for record in transaction:
                      data += self._record_encode(record)
              data += self._record_encode(group.group_trailer)
          data += self._record_encode(transmission.trailer)
          return data