code: func parsePermanodeContinueToken(v string) (t time.Time, br blob.Ref, ok bool) {
  	if !strings.HasPrefix(v, "pn:") {
  		return
  	}
  	v = v[len("pn:"):]
  	col := strings.Index(v, ":")
  	if col < 0 {
  		return
  	}
  	nano, err := strconv.ParseUint(v[:col], 10, 64)
  	if err != nil {
  		return
  	}
  	t = time.Unix(0, int64(nano))
  	br, ok = blob.Parse(v[col+1:])
  	return
  }
docs: // For permanodes, the continue token is (currently!)
  // of form "pn:nnnnnnn:sha1-xxxxx" where "pn" is a
  // literal, "nnnnnn" is the UnixNano of the time
  // (modified or created) and "sha1-xxxxx" was the item
  // seen in the final result set, used as a tie breaker
  // if multiple permanodes had the same mod/created
  // time. This format is NOT an API promise or standard and
  // clients should not rely on it. It may change without notice