code: func ParseLiteralSource(source string) (keyName, value string, err error) {
  	// leading equal is invalid
  	if strings.Index(source, "=") == 0 {
  		return "", "", fmt.Errorf("invalid literal source %v, expected key=value", source)
  	}
  	// split after the first equal (so values can have the = character)
  	items := strings.SplitN(source, "=", 2)
  	if len(items) != 2 {
  		return "", "", fmt.Errorf("invalid literal source %v, expected key=value", source)
  	}
  
  	return items[0], items[1], nil
  }
docs: // ParseLiteralSource parses the source key=val pair into its component pieces.
  // This functionality is distinguished from strings.SplitN(source, "=", 2) since
  // it returns an error in the case of empty keys, values, or a missing equals sign.