docs: def _add_data_attribute(self, data_attr):
          """Add a data attribute to the datastream structure.
  
          Data attributes require processing before they can be interpreted as
          datastream. This function grants that it is adding the attribute to
          the correct datastream or creating a new datastream if necessary.
          """
          attr_name = data_attr.header.attr_name
  
          stream = self._find_datastream(attr_name)
          if stream is None:
              stream = Datastream(attr_name)
              self.data_streams.append(stream)
          stream.add_data_attribute(data_attr)