code: func (fs *FlagSet) Usage() string {
  	var flags []string
  
  	// If there is no "help" flag defined, we will use it to display help/usage
  	// (default FlagSet).
  	if fs.F.Lookup("help") == nil {
  		flags = append(flags, "help")
  	}
  
  	fs.F.VisitAll(func(f *flag.Flag) {
  		comma := ""
  		if len(flags) > 0 {
  			comma = ","
  		}
  		flags = append(flags, fmt.Sprintf("[%s%s]", comma, f.Name))
  	})
  	return strings.Join(flags, "")
  }
docs: // Usage constructs a one-line usage string for all of the options defined in
  // Flags.