by construction. The escapes <code>\u</code> and <code>\U</code>
represent Unicode code points so within them some values are illegal,
in particular those above <code>0x10FFFF</code> and surrogate halves.
</p>

<p>
After a backslash, certain single-character escapes represent special values:
</p>

<pre class="grammar">
\a   U+0007 alert or bell
\b   U+0008 backspace
\f   U+000C form feed

		{"☻x\xe2\x98x", '�', len("☻x")},

		// Invalid rune values should never match.
		{"a☺b☻c☹d\xe2\x98�\xff�\xed\xa0\x80", -1, -1},
		{"a☺b☻c☹d\xe2\x98�\xff�\xed\xa0\x80", 0xD800, -1}, // Surrogate pair
		{"a☺b☻c☹d\xe2\x98�\xff�\xed\xa0\x80", utf8.MaxRune + 1, -1},
	}
	for _, tt := range tests {
		if got := IndexRune([]byte(tt.in), tt.rune); got != tt.want {

by construction. The escapes <code>\u</code> and <code>\U</code>
represent Unicode code points so within them some values are illegal,
in particular those above <code>0x10FFFF</code> and surrogate halves.
</p>

<p>
After a backslash, certain single-character escapes represent special values:
</p>

<pre class="grammar">
\a   U+0007 alert or bell
\b   U+0008 backspace
\f   U+000C form feed

pkg unicode/utf16, func DecodeRune(int32, int32) int32
pkg unicode/utf16, func Encode([]int32) []uint16
pkg unicode/utf16, func EncodeRune(int32) (int32, int32)
pkg unicode/utf16, func IsSurrogate(int32) bool
pkg unicode/utf8, const MaxRune ideal-char
pkg unicode/utf8, const RuneError ideal-char
pkg unicode/utf8, const RuneSelf ideal-int
pkg unicode/utf8, const UTFMax ideal-int