case 1:
			if i > 0 && x[i-1] == 'x' {
				copy(x[i-1:], "χ")
				break
			}
			fallthrough
		default:
			x[i] = 'x'
		}
	}
	return x
}

var makeFieldsInputASCII = func() []byte {
	x := make([]byte, 1<<20)
	// Input is ~10% space, rest ASCII non-space.
	r := rand.New(rand.NewSource(99))
	for i := range x {
		if r.Intn(10) == 0 {
			x[i] = ' '
		} else {