if rune == utf8.RuneError && size == 1 {
			return &Error{Code: ErrInvalidUTF8, Expr: s}
		}
		s = s[size:]
	}
	return nil
}

func nextRune(s string) (c rune, t string, err error) {
	c, size := utf8.DecodeRuneInString(s)
	if c == utf8.RuneError && size == 1 {
		return 0, "", &Error{Code: ErrInvalidUTF8, Expr: s}
	}
	return c, s[size:], nil
}

func isalnum(c rune) bool {

		{"ErrInvalidEscape", Const, 0},
		{"ErrInvalidNamedCapture", Const, 0},
		{"ErrInvalidPerlOp", Const, 0},
		{"ErrInvalidRepeatOp", Const, 0},
		{"ErrInvalidRepeatSize", Const, 0},
		{"ErrInvalidUTF8", Const, 0},
		{"ErrLarge", Const, 20},
		{"ErrMissingBracket", Const, 0},
		{"ErrMissingParen", Const, 0},
		{"ErrMissingRepeatArgument", Const, 0},
		{"ErrNestingDepth", Const, 19},

pkg regexp/syntax, const ErrInvalidPerlOp ErrorCode
pkg regexp/syntax, const ErrInvalidRepeatOp ErrorCode
pkg regexp/syntax, const ErrInvalidRepeatSize ErrorCode
pkg regexp/syntax, const ErrInvalidUTF8 ErrorCode
pkg regexp/syntax, const ErrMissingBracket ErrorCode
pkg regexp/syntax, const ErrMissingParen ErrorCode
pkg regexp/syntax, const ErrMissingRepeatArgument ErrorCode

pkg regexp/syntax, const ErrInvalidRepeatOp = "invalid nested repetition operator"
pkg regexp/syntax, const ErrInvalidRepeatSize = "invalid repeat count"
pkg regexp/syntax, const ErrInvalidUTF8 = "invalid UTF-8"
pkg regexp/syntax, const ErrMissingBracket = "missing closing ]"
pkg regexp/syntax, const ErrMissingParen = "missing closing )"