Op   InstOp
	Out  uint32 // all but InstMatch, InstFail
	Arg  uint32 // InstAlt, InstAltMatch, InstCapture, InstEmptyWidth
	Rune []rune
}

func (p *Prog) String() string {
	var b strings.Builder
	dumpProg(&b, p)
	return b.String()
}

// skipNop follows any no-op or capturing instructions.
func (p *Prog) skipNop(pc uint32) *Inst {
	i := &p.Inst[pc]
	for i.Op == InstNop || i.Op == InstCapture {