code: func getParentIDs(root, id string) ([]string, error) {
  	f, err := os.Open(path.Join(root, "layers", id))
  	if err != nil {
  		return nil, err
  	}
  	defer f.Close()
  
  	var out []string
  	s := bufio.NewScanner(f)
  
  	for s.Scan() {
  		if t := s.Text(); t != "" {
  			out = append(out, s.Text())
  		}
  	}
  	return out, s.Err()
  }
docs: // Read the layers file for the current id and return all the
  // layers represented by new lines in the file
  //
  // If there are no lines in the file then the id has no parent
  // and an empty slice is returned.