code: func replaceInvalidUTF8(input []byte) string {
  	var b strings.Builder
  
  	// Ranging over a string in Go produces runes. When the range keyword
  	// encounters an invalid UTF-8 encoding, it returns REPLACEMENT CHARACTER.
  	for _, v := range string(input) {
  		b.WriteRune(v)
  	}
  	return b.String()
  }
docs: // replaceInvalidUTF8 replaces all invalid UTF-8 encodings with
  // Unicode REPLACEMENT CHARACTER.