code: func (r *readlineUI) PrintErr(args ...interface{}) {
  	text := fmt.Sprint(args...)
  	if !strings.HasSuffix(text, "\n") {
  		text += "\n"
  	}
  	if readline.IsTerminal(int(syscall.Stderr)) {
  		text = colorize(text)
  	}
  	fmt.Fprint(r.rl.Stderr(), text)
  }
docs: // PrintErr shows a message to the user, colored in red for emphasis.
  // It is printed over stderr as stdout is reserved for regular output.