code: func parseGroup(row string) (*Group, error) {
  	fields := strings.Split(row, ":")
  	if len(fields) != 4 {
  		return nil, rowError{_GROUP_FILE, row}
  	}
  
  	gid, err := strconv.Atoi(fields[2])
  	if err != nil {
  		return nil, atoiError{_GROUP_FILE, row, "GID"}
  	}
  
  	return &Group{
  		Name:     fields[0],
  		password: fields[1],
  		GID:      gid,
  		UserList: strings.Split(fields[3], ","),
  	}, nil
  }
docs: // parseGroup parses the row of a group.