code: func (fs *FlagSet) ReportError(str string, withHelp bool) {
  	if withHelp {
  		if os.Args[0] == fs.Name() {
  			str += ".\nSee '" + os.Args[0] + " --help'"
  		} else {
  			str += ".\nSee '" + os.Args[0] + " " + fs.Name() + " --help'"
  		}
  	}
  	fmt.Fprintf(fs.Out(), "%s: %s.\n", os.Args[0], str)
  }
docs: // ReportError is a utility method that prints a user-friendly message
  // containing the error that occurred during parsing and a suggestion to get help