code: func (t *markedTag) genID() {
  	h := sha256.New()
  	fmt.Fprintf(h, "%d\n%s", t.Job, t.Key.Encode())
  	t.ID = base64.RawURLEncoding.EncodeToString(h.Sum(nil))
  }
docs: // genID derives an ID for this markedTag entity.
  //
  // Called internally by visitAndMarkTags().
  //
  // Each unique tag marked by some particular job gets its own key, i.e. each
  // job has its own namespace for marked tags.