// If the first byte is hex and the second is not, processing stops.
func (s *ss) hexByte() (b byte, ok bool) {
	rune1 := s.getRune()
	if rune1 == eof {
		return
	}
	value1, ok := hexDigit(rune1)
	if !ok {
		s.UnreadRune()
		return
	}
	value2, ok := hexDigit(s.mustReadRune())
	if !ok {
		s.errorString("illegal hex digit")
		return
	}

	bn := rb.rune[pos].pos
	sz := utf8.EncodeRune(rb.byte[bn:], rune(r))
	rb.rune[pos] = Properties{pos: bn, size: uint8(sz)}
}

// runeAt returns the rune at position n. It is used for Hangul and recomposition.
func (rb *reorderBuffer) runeAt(n int) rune {
	inf := rb.rune[n]
	r, _ := utf8.DecodeRune(rb.byte[inf.pos : inf.pos+inf.size])
	return r
}

	bn := rb.rune[pos].pos
	sz := utf8.EncodeRune(rb.byte[bn:], rune(r))
	rb.rune[pos] = Properties{pos: bn, size: uint8(sz)}
}

// runeAt returns the rune at position n. It is used for Hangul and recomposition.
func (rb *reorderBuffer) runeAt(n int) rune {
	inf := rb.rune[n]
	r, _ := utf8.DecodeRune(rb.byte[inf.pos : inf.pos+inf.size])
	return r
}

			if syntax.Flags(inst.Arg)&syntax.FoldCase != 0 {
				r0 := inst.Rune[0]
				runes = append(runes, r0, r0)
				for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
					runes = append(runes, r1, r1)
				}
				slices.Sort(runes)
			} else {
				runes = append(runes, inst.Rune[0], inst.Rune[0])
			}
			onePassRunes[pc] = runes
			inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
			for i := range inst.Next {

	case OpLiteral:
		for _, r := range re.Rune {
			escape(b, r, false)
		}
	case OpCharClass:
		if len(re.Rune)%2 != 0 {
			b.WriteString(`[invalid char class]`)
			break
		}
		b.WriteRune('[')
		if len(re.Rune) == 0 {
			b.WriteString(`^\x00-\x{10FFFF}`)
		} else if re.Rune[0] == 0 && re.Rune[len(re.Rune)-1] == unicode.MaxRune && len(re.Rune) > 2 {
			// Contains 0 and MaxRune. Probably a negated class.

		} else {
			curDir = RightToLeft
		}
		if curDir != prevDir {
			if i > 0 {
				o.runes = append(o.runes, runes[prevI:i])
				o.directions = append(o.directions, prevDir)
				o.startpos = append(o.startpos, prevI)
			}
			prevI = i
			prevDir = curDir
		}
	}
	o.runes = append(o.runes, runes[prevI:])
	o.directions = append(o.directions, prevDir)
	o.startpos = append(o.startpos, prevI)
	return o

		partLen = c.Rand.Intn(63) + 1 // len is [1, 63]
	}

	runes := make([]rune, partLen)
	if partLen == 0 {
		return string(runes)
	}

	runes[0] = validStartEnd[c.Rand.Intn(len(validStartEnd))].choose(c.Rand)
	for i := range runes[1:] {
		runes[i+1] = validMiddle[c.Rand.Intn(len(validMiddle))].choose(c.Rand)
	}
	runes[len(runes)-1] = validStartEnd[c.Rand.Intn(len(validStartEnd))].choose(c.Rand)

				// is odd so we take the low bit from _case.
				return rune(cr.Lo) + ((r-rune(cr.Lo))&^1 | rune(_case&1)), true
			}
			return r + delta, true
		}
		if r < rune(cr.Lo) {
			hi = m
		} else {
			lo = m + 1
		}
	}
	return r, false
}

// To maps the rune to the specified case: [UpperCase], [LowerCase], or [TitleCase].
func To(_case int, r rune) rune {
	r, _ = to(_case, r, CaseRanges)
	return r
}

		return rune(p0&mask2)<<6 | rune(b1&maskx), 2
	}
	b2 := p[2]
	if b2 < locb || hicb < b2 {
		return RuneError, 1
	}
	if sz <= 3 {
		return rune(p0&mask3)<<12 | rune(b1&maskx)<<6 | rune(b2&maskx), 3
	}
	b3 := p[3]
	if b3 < locb || hicb < b3 {
		return RuneError, 1
	}
	return rune(p0&mask4)<<18 | rune(b1&maskx)<<12 | rune(b2&maskx)<<6 | rune(b3&maskx), 4
}

		}
		t.historyIndex++
		runes := []rune(entry)
		t.setLine(runes, len(runes))
	case keyDown:
		switch t.historyIndex {
		case -1:
			return
		case 0:
			runes := []rune(t.historyPending)
			t.setLine(runes, len(runes))
			t.historyIndex--
		default:
			entry, ok := t.history.NthPreviousEntry(t.historyIndex - 1)
			if ok {
				t.historyIndex--
				runes := []rune(entry)