code: func printCharCode(code rune) string {
  	// print as ASCII for printable range
  	if code >= 0x0020 {
  		return fmt.Sprintf(`%c`, code)
  	}
  	// Otherwise print the escaped form. e.g. `"\\u0007"`
  	return fmt.Sprintf(`\u%04X`, code)
  }
docs: // printCharCode here is slightly different from lexer.printCharCode()