// must be considered UTF-8 encoding (i.e., not compatible with CP-437, ASCII,
// or any other common encoding).
func detectUTF8(s string) (valid, require bool) {
	for i := 0; i < len(s); {
		r, size := utf8.DecodeRuneInString(s[i:])
		i += size
		// Officially, ZIP uses CP-437, but many readers use the system's
		// local character encoding. Most encoding are compatible with a large
		// subset of CP-437, which itself is ASCII-like.

	case scanner.Int:
		return p.atoi(tok.String())
	case scanner.Char:
		str, err := strconv.Unquote(tok.String())
		if err != nil {
			p.errorf("%s", err)
		}
		r, w := utf8.DecodeRuneInString(str)
		if w == 1 && r == utf8.RuneError {
			p.errorf("illegal UTF-8 encoding for character constant")
		}
		return uint64(r)
	case '+':
		return +p.factor()
	case '-':
		return -p.factor()

pkg unicode/utf8, func DecodeLastRune([]uint8) (int32, int)
pkg unicode/utf8, func DecodeLastRuneInString(string) (int32, int)
pkg unicode/utf8, func DecodeRune([]uint8) (int32, int)
pkg unicode/utf8, func DecodeRuneInString(string) (int32, int)
pkg unicode/utf8, func EncodeRune([]uint8, int32) int
pkg unicode/utf8, func FullRune([]uint8) bool
pkg unicode/utf8, func FullRuneInString(string) bool