if err != nil {
		return batch{}, 0, err
	}
	if typ := event.Type(b); typ != go122.EvEventBatch && typ != go122.EvExperimentalBatch {
		return batch{}, 0, fmt.Errorf("expected batch event, got %s", go122.EventString(typ))
	}

	// Read the experiment of we have one.
	exp := event.NoExperiment
	if event.Type(b) == go122.EvExperimentalBatch {
		e, err := r.ReadByte()
		if err != nil {
			return batch{}, 0, err
		}