// own keys and assigning certain semantic meaning to the associated values.
	// For example, sparse file support in PAX is implemented using keys
	// defined by the GNU manual (e.g., "GNU.sparse.map").
	//
	// Reference:
	//	http://pubs.opengroup.org/onlinepubs/009695399/utilities/pax.html
	FormatPAX

	// FormatGNU represents the GNU header format.
	//

	// 1.  Grow. This triggers two reallocations in Map.
	maxRune := func(r rune) rune { return unicode.MaxRune }
	m := Map(maxRune, []byte(a))
	expect := tenRunes(unicode.MaxRune)
	if string(m) != expect {
		t.Errorf("growing: expected %q got %q", expect, m)
	}

	// 2. Shrink
	minRune := func(r rune) rune { return 'a' }
	m = Map(minRune, []byte(tenRunes(unicode.MaxRune)))
	expect = a

	rot13 := func(r rune) rune {
		switch {
		case r >= 'A' && r <= 'Z':
			return 'A' + (r-'A'+13)%26
		case r >= 'a' && r <= 'z':
			return 'a' + (r-'a'+13)%26
		}
		return r
	}
	fmt.Printf("%s\n", bytes.Map(rot13, []byte("'Twas brillig and the slithy gopher...")))
	// Output:
	// 'Gjnf oevyyvt naq gur fyvgul tbcure...
}

func ExampleReader_Len() {
	fmt.Println(bytes.NewReader([]byte("Hi!")).Len())

</p>

<p>
The most important thing to know about Go's assembler is that it is not a direct representation of the underlying machine.
Some of the details map precisely to the machine, but some do not.
This is because the compiler suite (see
<a href="https://9p.io/sys/doc/compiler.html">this description</a>)
needs no assembler pass in the usual pipeline.

// (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.
//	Pointer to array: the number of elements in *v (even if v is nil).
//	Slice, or map: the number of elements in v; if v is nil, len(v) is zero.

func (tw *Writer) writePAXHeader(hdr *Header, paxHdrs map[string]string) error {
	realName, realSize := hdr.Name, hdr.Size

	// TODO(dsnet): Re-enable this when adding sparse support.
	// See https://golang.org/issue/22735
	/*
		// Handle sparse files.
		var spd sparseDatas
		var spb []byte
		if len(hdr.SparseHoles) > 0 {
			sph := append([]sparseEntry{}, hdr.SparseHoles...) // Copy sparse map
			sph = alignSparseEntries(sph, hdr.Size)

		beginningOfLine: true,
		macros:          predefine(flags.D),
	}
}

// predefine installs the macros set by the -D flag on the command line.
func predefine(defines flags.MultiFlag) map[string]*Macro {
	macros := make(map[string]*Macro)
	for _, name := range defines {
		value := "1"
		i := strings.IndexRune(name, '=')
		if i > 0 {
			name, value = name[:i], name[i+1:]
		}
		tokens := Tokenize(name)

implements the interface.
</p>

<h3 id="Map_types">Map types</h3>

<p>
A map is an unordered group of elements of one type, called the
element type, indexed by a set of unique <i>keys</i> of another type,
called the key type.
The value of an uninitialized map is <code>nil</code>.
</p>

<pre class="ebnf">
MapType     = "map" "[" KeyType "]" ElementType .
KeyType     = Type .
</pre>

}

// Map returns a copy of the byte slice s with all its characters modified
// according to the mapping function. If mapping returns a negative value, the character is
// dropped from the byte slice with no replacement. The characters in s and the
// output are interpreted as UTF-8-encoded code points.
func Map(mapping func(r rune) rune, s []byte) []byte {

pkg syscall (darwin-386), const MAP_ANON = 4096
pkg syscall (darwin-386), const MAP_COPY = 2
pkg syscall (darwin-386), const MAP_FILE = 0
pkg syscall (darwin-386), const MAP_FIXED = 16
pkg syscall (darwin-386), const MAP_HASSEMAPHORE = 512
pkg syscall (darwin-386), const MAP_JIT = 2048
pkg syscall (darwin-386), const MAP_NOCACHE = 1024
pkg syscall (darwin-386), const MAP_NOEXTEND = 256