f.walk(&n.X, context, visit)
	case *ast.UnaryExpr:
		f.walk(&n.X, ctxExpr, visit)
	case *ast.BinaryExpr:
		f.walk(&n.X, ctxExpr, visit)
		f.walk(&n.Y, ctxExpr, visit)
	case *ast.KeyValueExpr:
		f.walk(&n.Key, ctxExpr, visit)
		f.walk(&n.Value, ctxExpr, visit)

	case *ast.ArrayType:
		f.walk(&n.Len, ctxExpr, visit)
		f.walk(&n.Elt, ctxType, visit)
	case *ast.StructType:
		f.walk(n.Fields, ctxField, visit)

	{"X14", "X14"},
	{"X15", "X15"},
	{"X2", "X2"},
	{"X3", "X3"},
	{"X4", "X4"},
	{"X5", "X5"},
	{"X6", "X6"},
	{"X7", "X7"},
	{"X8", "X8"},
	{"X9", "X9"},
	{"_expand_key_128<>(SB)", "_expand_key_128<>(SB)"},
	{"_seek<>(SB)", "_seek<>(SB)"},
	{"a2+16(FP)", "a2+16(FP)"},
	{"addr2+24(FP)", "addr2+24(FP)"},
	{"asmcgocall<>(SB)", "asmcgocall<>(SB)"},
	{"b+24(FP)", "b+24(FP)"},

because it documents the full list of known GODEBUG settings,
which are tied to a specific release.
-->

## Introduction {#intro}

Go's emphasis on backwards compatibility is one of its key strengths.
There are, however, times when we cannot maintain complete compatibility.
If code depends on buggy (including insecure) behavior,
then fixing the bug will break that code.
New features can also have similar impacts:

	TypeFifo    = '6' // FIFO node

	// Type '7' is reserved.
	TypeCont = '7'

	// Type 'x' is used by the PAX format to store key-value records that
	// are only relevant to the next file.
	// This package transparently handles these types.
	TypeXHeader = 'x'

	// Type 'g' is used by the PAX format to store key-value records that
	// are relevant to all subsequent files.
	// This package only supports parsing and composing such headers,

// len(src) and len(dst).
func copy(dst, src []Type) int

// The delete built-in function deletes the element with the specified key
// (m[key]) from the map. If m is nil or there is no such element, delete
// is a no-op.
func delete(m map[Type]Type1, key Type)

// The len built-in function returns the length of v, according to its type:
//
//	Array: the number of elements in v.

	FormatUSTAR

	// FormatPAX represents the PAX header format defined in POSIX.1-2001.
	//
	// PAX extends USTAR by writing a special file with Typeflag TypeXHeader
	// preceding the original header. This file contains a set of key-value
	// records, which are used to overcome USTAR's shortcomings, in addition to
	// providing the ability to have sub-second resolution for timestamps.
	//
	// Some newer formats add their own extensions to PAX by defining their

<code>MOVQ</code> <code>$0,</code> <code>CX</code> clears <code>CX</code>.
This rule applies even on architectures where the conventional notation uses the opposite direction.
</p>

<p>
Here follow some descriptions of key Go-specific details for the supported architectures.
</p>

<h3 id="x86">32-bit Intel 386</h3>

<p>
The runtime pointer to the <code>g</code> structure is maintained

	}

	// Look in cache.
	// If we've already done an import with the same set
	// of relevant tags, reuse the result.
	var key string
	if usePkgCache {
		if tags, ok := pkgTags[dir]; ok {
			key = tagKey(dir, context, tags)
			if pkg := pkgCache[key]; pkg != nil {
				w.imported[name] = pkg
				return pkg, nil
			}
		}
	}

	info, err := context.ImportDir(dir, 0)
	if err != nil {

	for len(sbuf) > 0 {
		key, value, residual, err := parsePAXRecord(sbuf)
		if err != nil {
			return nil, ErrHeader
		}
		sbuf = residual

		switch key {
		case paxGNUSparseOffset, paxGNUSparseNumBytes:
			// Validate sparse header order and value.
			if (len(sparseMap)%2 == 0 && key != paxGNUSparseOffset) ||
				(len(sparseMap)%2 == 1 && key != paxGNUSparseNumBytes) ||

				break
			}
		}
		if !ok {
			t.Errorf("%s: have encoding %s, want %s", p, codeHex, hexes)
		}
	}

	if len(hexByLine) > 0 {
		var missing []string
		for key := range hexByLine {
			missing = append(missing, key)
		}
		sort.Strings(missing)
		for _, line := range missing {
			t.Errorf("%s: did not find instruction encoding", line)
		}
	}

}

func isHexes(s string) bool {