code: func (t *tx) StartExternal(host, name string) error {
  	t.mtx.Lock()
  	defer t.mtx.Unlock()
  
  	id, err := t.Tracer.BeginExternalSegment(t.id, t.ss.Peek(), host, name)
  	if err != nil {
  		return err
  	}
  	t.ss.Push(id)
  	return nil
  }
docs: // StartExternal starts an external segment.