code: func groupOptions(vars variables) map[string][]string {
  	groups := make(map[string][]string)
  	for name, option := range vars {
  		group := option.group
  		if group != "" {
  			groups[group] = append(groups[group], name)
  		}
  	}
  	for _, names := range groups {
  		sort.Strings(names)
  	}
  	return groups
  }
docs: // groupOptions returns a map containing all non-empty groups
  // mapped to an array of the option names in that group in
  // sorted order.