2	rune1 "a" -> 3
  3	alt -> 2, 4
  4	cap 3 -> 5
  5	cap 4 -> 6
  6	rune1 "b" -> 7
  7	alt -> 6, 8
  8	cap 5 -> 9
  9	match
`},
	{"a+|b+", `  0	fail
  1	rune1 "a" -> 2
  2	alt -> 1, 6
  3	rune1 "b" -> 4
  4	alt -> 3, 6
  5*	alt -> 1, 3
  6	match
`},
	{"A[Aa]", `  0	fail
  1*	rune1 "A" -> 2
  2	rune "A"/i -> 3
  3	match
`},
	{"(?:(?:^).)", `  0	fail
  1*	empty 4 -> 2
  2	anynotnl -> 3
  3	match

	case InstNop:
		bw(b, "nop -> ", u32(i.Out))
	case InstRune:
		if i.Rune == nil {
			// shouldn't happen
			bw(b, "rune <nil>")
		}
		bw(b, "rune ", strconv.QuoteToASCII(string(i.Rune)))
		if Flags(i.Arg)&FoldCase != 0 {
			bw(b, "/i")
		}
		bw(b, " -> ", u32(i.Out))
	case InstRune1:
		bw(b, "rune1 ", strconv.QuoteToASCII(string(i.Rune)), " -> ", u32(i.Out))
	case InstRuneAny:
		bw(b, "any -> ", u32(i.Out))

// 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
	}

// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Test rune constants, expressions and types.
// Compiles but does not run.

package rune

var (
	r0 = 'a'
	r1 = 'a'+1
	r2 = 1+'a'
	r3 = 'a'*2
	r4 = 'a'/2
	r5 = 'a'<<1
	r6 = 'b'<<2
	r7 int32

	r = []rune{r0, r1, r2, r3, r4, r5, r6, r7}
)

var (
	f0 = 1.2
	f1 = 1.2/'a'

	f = []float64{f0, f1}

	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
}

	p.numRunes += len(re.Rune)
	if re.Op == OpCharClass && len(re.Rune) == 2 && re.Rune[0] == re.Rune[1] {
		// Single rune.
		if p.maybeConcat(re.Rune[0], p.flags&^FoldCase) {
			return nil
		}
		re.Op = OpLiteral
		re.Rune = re.Rune[:1]
		re.Flags = p.flags &^ FoldCase
	} else if re.Op == OpCharClass && len(re.Rune) == 4 &&
		re.Rune[0] == re.Rune[1] && re.Rune[2] == re.Rune[3] &&

			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 {

	_ = myString([]myByte{'\xf0', '\x9f', '\x8c', '\x8d'}) // "🌍

	// 3
	_ = string([]rune{0x767d, 0x9d6c, 0x7fd4}) // "\u767d\u9d6c\u7fd4" == "白鵬翔"
	_ = string([]rune{})                       // ""
	_ = string([]rune(nil))                    // ""

	type runes []rune
	_ = string(runes{0x767d, 0x9d6c, 0x7fd4}) // "\u767d\u9d6c\u7fd4" == "白鵬翔"

	type myRune rune
	_ = string([]myRune{0x266b, 0x266c}) // "\u266b\u266c" == "♫♬"

	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.