code: func extractSubTangleMilestoneIndex(data []byte) (uint64, error) {
  	lastColonIndex := bytes.LastIndex(data, colonSep[:])
  	if lastColonIndex == -1 {
  		return 0, errors.Wrap(ErrNoLatestSolidSubtangleInfo, "unable to find index")
  	}
  	index := data[lastColonIndex+1 : len(data)-1]
  	return strconv.ParseUint(string(index), 10, 64)
  }
docs: // extracts the latest solid subtangle milestone index of a reduced getNodeInfo response