r := rune(s[0])
		if r >= utf8.RuneSelf {
			// search utf8.RuneError.
			for _, r = range chars {
				if r == utf8.RuneError {
					return 0
				}
			}
			return -1
		}
		if bytealg.IndexByteString(chars, s[0]) >= 0 {
			return 0
		}
		return -1
	}
	if len(chars) == 1 {
		r := rune(chars[0])
		if r >= utf8.RuneSelf {
			r = utf8.RuneError
		}
		return IndexRune(s, r)
	}