Adding upstream version 1.22.1.upstream/1.22.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

29 files changed, 16981 insertions, 0 deletions

diff --git a/src/regexp/all_test.go b/src/regexp/all_test.go
new file mode 100644
index 0000000..124313d
--- /dev/null
+++ b/src/regexp/all_test.go
@@ -0,0 +1,975 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package regexp
+
+import (
+	"reflect"
+	"regexp/syntax"
+	"strings"
+	"testing"
+	"unicode/utf8"
+)
+
+var goodRe = []string{
+	``,
+	`.`,
+	`^.$`,
+	`a`,
+	`a*`,
+	`a+`,
+	`a?`,
+	`a|b`,
+	`a*|b*`,
+	`(a*|b)(c*|d)`,
+	`[a-z]`,
+	`[a-abc-c\-\]\[]`,
+	`[a-z]+`,
+	`[abc]`,
+	`[^1234]`,
+	`[^\n]`,
+	`\!\\`,
+}
+
+type stringError struct {
+	re  string
+	err string
+}
+
+var badRe = []stringError{
+	{`*`, "missing argument to repetition operator: `*`"},
+	{`+`, "missing argument to repetition operator: `+`"},
+	{`?`, "missing argument to repetition operator: `?`"},
+	{`(abc`, "missing closing ): `(abc`"},
+	{`abc)`, "unexpected ): `abc)`"},
+	{`x[a-z`, "missing closing ]: `[a-z`"},
+	{`[z-a]`, "invalid character class range: `z-a`"},
+	{`abc\`, "trailing backslash at end of expression"},
+	{`a**`, "invalid nested repetition operator: `**`"},
+	{`a*+`, "invalid nested repetition operator: `*+`"},
+	{`\x`, "invalid escape sequence: `\\x`"},
+	{strings.Repeat(`\pL`, 27000), "expression too large"},
+}
+
+func compileTest(t *testing.T, expr string, error string) *Regexp {
+	re, err := Compile(expr)
+	if error == "" && err != nil {
+		t.Error("compiling `", expr, "`; unexpected error: ", err.Error())
+	}
+	if error != "" && err == nil {
+		t.Error("compiling `", expr, "`; missing error")
+	} else if error != "" && !strings.Contains(err.Error(), error) {
+		t.Error("compiling `", expr, "`; wrong error: ", err.Error(), "; want ", error)
+	}
+	return re
+}
+
+func TestGoodCompile(t *testing.T) {
+	for i := 0; i < len(goodRe); i++ {
+		compileTest(t, goodRe[i], "")
+	}
+}
+
+func TestBadCompile(t *testing.T) {
+	for i := 0; i < len(badRe); i++ {
+		compileTest(t, badRe[i].re, badRe[i].err)
+	}
+}
+
+func matchTest(t *testing.T, test *FindTest) {
+	re := compileTest(t, test.pat, "")
+	if re == nil {
+		return
+	}
+	m := re.MatchString(test.text)
+	if m != (len(test.matches) > 0) {
+		t.Errorf("MatchString failure on %s: %t should be %t", test, m, len(test.matches) > 0)
+	}
+	// now try bytes
+	m = re.Match([]byte(test.text))
+	if m != (len(test.matches) > 0) {
+		t.Errorf("Match failure on %s: %t should be %t", test, m, len(test.matches) > 0)
+	}
+}
+
+func TestMatch(t *testing.T) {
+	for _, test := range findTests {
+		matchTest(t, &test)
+	}
+}
+
+func matchFunctionTest(t *testing.T, test *FindTest) {
+	m, err := MatchString(test.pat, test.text)
+	if err == nil {
+		return
+	}
+	if m != (len(test.matches) > 0) {
+		t.Errorf("Match failure on %s: %t should be %t", test, m, len(test.matches) > 0)
+	}
+}
+
+func TestMatchFunction(t *testing.T) {
+	for _, test := range findTests {
+		matchFunctionTest(t, &test)
+	}
+}
+
+func copyMatchTest(t *testing.T, test *FindTest) {
+	re := compileTest(t, test.pat, "")
+	if re == nil {
+		return
+	}
+	m1 := re.MatchString(test.text)
+	m2 := re.Copy().MatchString(test.text)
+	if m1 != m2 {
+		t.Errorf("Copied Regexp match failure on %s: original gave %t; copy gave %t; should be %t",
+			test, m1, m2, len(test.matches) > 0)
+	}
+}
+
+func TestCopyMatch(t *testing.T) {
+	for _, test := range findTests {
+		copyMatchTest(t, &test)
+	}
+}
+
+type ReplaceTest struct {
+	pattern, replacement, input, output string
+}
+
+var replaceTests = []ReplaceTest{
+	// Test empty input and/or replacement, with pattern that matches the empty string.
+	{"", "", "", ""},
+	{"", "x", "", "x"},
+	{"", "", "abc", "abc"},
+	{"", "x", "abc", "xaxbxcx"},
+
+	// Test empty input and/or replacement, with pattern that does not match the empty string.
+	{"b", "", "", ""},
+	{"b", "x", "", ""},
+	{"b", "", "abc", "ac"},
+	{"b", "x", "abc", "axc"},
+	{"y", "", "", ""},
+	{"y", "x", "", ""},
+	{"y", "", "abc", "abc"},
+	{"y", "x", "abc", "abc"},
+
+	// Multibyte characters -- verify that we don't try to match in the middle
+	// of a character.
+	{"[a-c]*", "x", "\u65e5", "x\u65e5x"},
+	{"[^\u65e5]", "x", "abc\u65e5def", "xxx\u65e5xxx"},
+
+	// Start and end of a string.
+	{"^[a-c]*", "x", "abcdabc", "xdabc"},
+	{"[a-c]*$", "x", "abcdabc", "abcdx"},
+	{"^[a-c]*$", "x", "abcdabc", "abcdabc"},
+	{"^[a-c]*", "x", "abc", "x"},
+	{"[a-c]*$", "x", "abc", "x"},
+	{"^[a-c]*$", "x", "abc", "x"},
+	{"^[a-c]*", "x", "dabce", "xdabce"},
+	{"[a-c]*$", "x", "dabce", "dabcex"},
+	{"^[a-c]*$", "x", "dabce", "dabce"},
+	{"^[a-c]*", "x", "", "x"},
+	{"[a-c]*$", "x", "", "x"},
+	{"^[a-c]*$", "x", "", "x"},
+
+	{"^[a-c]+", "x", "abcdabc", "xdabc"},
+	{"[a-c]+$", "x", "abcdabc", "abcdx"},
+	{"^[a-c]+$", "x", "abcdabc", "abcdabc"},
+	{"^[a-c]+", "x", "abc", "x"},
+	{"[a-c]+$", "x", "abc", "x"},
+	{"^[a-c]+$", "x", "abc", "x"},
+	{"^[a-c]+", "x", "dabce", "dabce"},
+	{"[a-c]+$", "x", "dabce", "dabce"},
+	{"^[a-c]+$", "x", "dabce", "dabce"},
+	{"^[a-c]+", "x", "", ""},
+	{"[a-c]+$", "x", "", ""},
+	{"^[a-c]+$", "x", "", ""},
+
+	// Other cases.
+	{"abc", "def", "abcdefg", "defdefg"},
+	{"bc", "BC", "abcbcdcdedef", "aBCBCdcdedef"},
+	{"abc", "", "abcdabc", "d"},
+	{"x", "xXx", "xxxXxxx", "xXxxXxxXxXxXxxXxxXx"},
+	{"abc", "d", "", ""},
+	{"abc", "d", "abc", "d"},
+	{".+", "x", "abc", "x"},
+	{"[a-c]*", "x", "def", "xdxexfx"},
+	{"[a-c]+", "x", "abcbcdcdedef", "xdxdedef"},
+	{"[a-c]*", "x", "abcbcdcdedef", "xdxdxexdxexfx"},
+
+	// Substitutions
+	{"a+", "($0)", "banana", "b(a)n(a)n(a)"},
+	{"a+", "(${0})", "banana", "b(a)n(a)n(a)"},
+	{"a+", "(${0})$0", "banana", "b(a)an(a)an(a)a"},
+	{"a+", "(${0})$0", "banana", "b(a)an(a)an(a)a"},
+	{"hello, (.+)", "goodbye, ${1}", "hello, world", "goodbye, world"},
+	{"hello, (.+)", "goodbye, $1x", "hello, world", "goodbye, "},
+	{"hello, (.+)", "goodbye, ${1}x", "hello, world", "goodbye, worldx"},
+	{"hello, (.+)", "<$0><$1><$2><$3>", "hello, world", "<hello, world><world><><>"},
+	{"hello, (?P<noun>.+)", "goodbye, $noun!", "hello, world", "goodbye, world!"},
+	{"hello, (?P<noun>.+)", "goodbye, ${noun}", "hello, world", "goodbye, world"},
+	{"(?P<x>hi)|(?P<x>bye)", "$x$x$x", "hi", "hihihi"},
+	{"(?P<x>hi)|(?P<x>bye)", "$x$x$x", "bye", "byebyebye"},
+	{"(?P<x>hi)|(?P<x>bye)", "$xyz", "hi", ""},
+	{"(?P<x>hi)|(?P<x>bye)", "${x}yz", "hi", "hiyz"},
+	{"(?P<x>hi)|(?P<x>bye)", "hello $$x", "hi", "hello $x"},
+	{"a+", "${oops", "aaa", "${oops"},
+	{"a+", "$$", "aaa", "$"},
+	{"a+", "$", "aaa", "$"},
+
+	// Substitution when subexpression isn't found
+	{"(x)?", "$1", "123", "123"},
+	{"abc", "$1", "123", "123"},
+
+	// Substitutions involving a (x){0}
+	{"(a)(b){0}(c)", ".$1|$3.", "xacxacx", "x.a|c.x.a|c.x"},
+	{"(a)(((b))){0}c", ".$1.", "xacxacx", "x.a.x.a.x"},
+	{"((a(b){0}){3}){5}(h)", "y caramb$2", "say aaaaaaaaaaaaaaaah", "say ay caramba"},
+	{"((a(b){0}){3}){5}h", "y caramb$2", "say aaaaaaaaaaaaaaaah", "say ay caramba"},
+}
+
+var replaceLiteralTests = []ReplaceTest{
+	// Substitutions
+	{"a+", "($0)", "banana", "b($0)n($0)n($0)"},
+	{"a+", "(${0})", "banana", "b(${0})n(${0})n(${0})"},
+	{"a+", "(${0})$0", "banana", "b(${0})$0n(${0})$0n(${0})$0"},
+	{"a+", "(${0})$0", "banana", "b(${0})$0n(${0})$0n(${0})$0"},
+	{"hello, (.+)", "goodbye, ${1}", "hello, world", "goodbye, ${1}"},
+	{"hello, (?P<noun>.+)", "goodbye, $noun!", "hello, world", "goodbye, $noun!"},
+	{"hello, (?P<noun>.+)", "goodbye, ${noun}", "hello, world", "goodbye, ${noun}"},
+	{"(?P<x>hi)|(?P<x>bye)", "$x$x$x", "hi", "$x$x$x"},
+	{"(?P<x>hi)|(?P<x>bye)", "$x$x$x", "bye", "$x$x$x"},
+	{"(?P<x>hi)|(?P<x>bye)", "$xyz", "hi", "$xyz"},
+	{"(?P<x>hi)|(?P<x>bye)", "${x}yz", "hi", "${x}yz"},
+	{"(?P<x>hi)|(?P<x>bye)", "hello $$x", "hi", "hello $$x"},
+	{"a+", "${oops", "aaa", "${oops"},
+	{"a+", "$$", "aaa", "$$"},
+	{"a+", "$", "aaa", "$"},
+}
+
+type ReplaceFuncTest struct {
+	pattern       string
+	replacement   func(string) string
+	input, output string
+}
+
+var replaceFuncTests = []ReplaceFuncTest{
+	{"[a-c]", func(s string) string { return "x" + s + "y" }, "defabcdef", "defxayxbyxcydef"},
+	{"[a-c]+", func(s string) string { return "x" + s + "y" }, "defabcdef", "defxabcydef"},
+	{"[a-c]*", func(s string) string { return "x" + s + "y" }, "defabcdef", "xydxyexyfxabcydxyexyfxy"},
+}
+
+func TestReplaceAll(t *testing.T) {
+	for _, tc := range replaceTests {
+		re, err := Compile(tc.pattern)
+		if err != nil {
+			t.Errorf("Unexpected error compiling %q: %v", tc.pattern, err)
+			continue
+		}
+		actual := re.ReplaceAllString(tc.input, tc.replacement)
+		if actual != tc.output {
+			t.Errorf("%q.ReplaceAllString(%q,%q) = %q; want %q",
+				tc.pattern, tc.input, tc.replacement, actual, tc.output)
+		}
+		// now try bytes
+		actual = string(re.ReplaceAll([]byte(tc.input), []byte(tc.replacement)))
+		if actual != tc.output {
+			t.Errorf("%q.ReplaceAll(%q,%q) = %q; want %q",
+				tc.pattern, tc.input, tc.replacement, actual, tc.output)
+		}
+	}
+}
+
+func TestReplaceAllLiteral(t *testing.T) {
+	// Run ReplaceAll tests that do not have $ expansions.
+	for _, tc := range replaceTests {
+		if strings.Contains(tc.replacement, "$") {
+			continue
+		}
+		re, err := Compile(tc.pattern)
+		if err != nil {
+			t.Errorf("Unexpected error compiling %q: %v", tc.pattern, err)
+			continue
+		}
+		actual := re.ReplaceAllLiteralString(tc.input, tc.replacement)
+		if actual != tc.output {
+			t.Errorf("%q.ReplaceAllLiteralString(%q,%q) = %q; want %q",
+				tc.pattern, tc.input, tc.replacement, actual, tc.output)
+		}
+		// now try bytes
+		actual = string(re.ReplaceAllLiteral([]byte(tc.input), []byte(tc.replacement)))
+		if actual != tc.output {
+			t.Errorf("%q.ReplaceAllLiteral(%q,%q) = %q; want %q",
+				tc.pattern, tc.input, tc.replacement, actual, tc.output)
+		}
+	}
+
+	// Run literal-specific tests.
+	for _, tc := range replaceLiteralTests {
+		re, err := Compile(tc.pattern)
+		if err != nil {
+			t.Errorf("Unexpected error compiling %q: %v", tc.pattern, err)
+			continue
+		}
+		actual := re.ReplaceAllLiteralString(tc.input, tc.replacement)
+		if actual != tc.output {
+			t.Errorf("%q.ReplaceAllLiteralString(%q,%q) = %q; want %q",
+				tc.pattern, tc.input, tc.replacement, actual, tc.output)
+		}
+		// now try bytes
+		actual = string(re.ReplaceAllLiteral([]byte(tc.input), []byte(tc.replacement)))
+		if actual != tc.output {
+			t.Errorf("%q.ReplaceAllLiteral(%q,%q) = %q; want %q",
+				tc.pattern, tc.input, tc.replacement, actual, tc.output)
+		}
+	}
+}
+
+func TestReplaceAllFunc(t *testing.T) {
+	for _, tc := range replaceFuncTests {
+		re, err := Compile(tc.pattern)
+		if err != nil {
+			t.Errorf("Unexpected error compiling %q: %v", tc.pattern, err)
+			continue
+		}
+		actual := re.ReplaceAllStringFunc(tc.input, tc.replacement)
+		if actual != tc.output {
+			t.Errorf("%q.ReplaceFunc(%q,fn) = %q; want %q",
+				tc.pattern, tc.input, actual, tc.output)
+		}
+		// now try bytes
+		actual = string(re.ReplaceAllFunc([]byte(tc.input), func(s []byte) []byte { return []byte(tc.replacement(string(s))) }))
+		if actual != tc.output {
+			t.Errorf("%q.ReplaceFunc(%q,fn) = %q; want %q",
+				tc.pattern, tc.input, actual, tc.output)
+		}
+	}
+}
+
+type MetaTest struct {
+	pattern, output, literal string
+	isLiteral                bool
+}
+
+var metaTests = []MetaTest{
+	{``, ``, ``, true},
+	{`foo`, `foo`, `foo`, true},
+	{`日本語+`, `日本語\+`, `日本語`, false},
+	{`foo\.\$`, `foo\\\.\\\$`, `foo.$`, true}, // has meta but no operator
+	{`foo.\$`, `foo\.\\\$`, `foo`, false},     // has escaped operators and real operators
+	{`!@#$%^&*()_+-=[{]}\|,<.>/?~`, `!@#\$%\^&\*\(\)_\+-=\[\{\]\}\\\|,<\.>/\?~`, `!@#`, false},
+}
+
+var literalPrefixTests = []MetaTest{
+	// See golang.org/issue/11175.
+	// output is unused.
+	{`^0^0$`, ``, `0`, false},
+	{`^0^`, ``, ``, false},
+	{`^0$`, ``, `0`, true},
+	{`$0^`, ``, ``, false},
+	{`$0$`, ``, ``, false},
+	{`^^0$$`, ``, ``, false},
+	{`^$^$`, ``, ``, false},
+	{`$$0^^`, ``, ``, false},
+	{`a\x{fffd}b`, ``, `a`, false},
+	{`\x{fffd}b`, ``, ``, false},
+	{"\ufffd", ``, ``, false},
+}
+
+func TestQuoteMeta(t *testing.T) {
+	for _, tc := range metaTests {
+		// Verify that QuoteMeta returns the expected string.
+		quoted := QuoteMeta(tc.pattern)
+		if quoted != tc.output {
+			t.Errorf("QuoteMeta(`%s`) = `%s`; want `%s`",
+				tc.pattern, quoted, tc.output)
+			continue
+		}
+
+		// Verify that the quoted string is in fact treated as expected
+		// by Compile -- i.e. that it matches the original, unquoted string.
+		if tc.pattern != "" {
+			re, err := Compile(quoted)
+			if err != nil {
+				t.Errorf("Unexpected error compiling QuoteMeta(`%s`): %v", tc.pattern, err)
+				continue
+			}
+			src := "abc" + tc.pattern + "def"
+			repl := "xyz"
+			replaced := re.ReplaceAllString(src, repl)
+			expected := "abcxyzdef"
+			if replaced != expected {
+				t.Errorf("QuoteMeta(`%s`).Replace(`%s`,`%s`) = `%s`; want `%s`",
+					tc.pattern, src, repl, replaced, expected)
+			}
+		}
+	}
+}
+
+func TestLiteralPrefix(t *testing.T) {
+	for _, tc := range append(metaTests, literalPrefixTests...) {
+		// Literal method needs to scan the pattern.
+		re := MustCompile(tc.pattern)
+		str, complete := re.LiteralPrefix()
+		if complete != tc.isLiteral {
+			t.Errorf("LiteralPrefix(`%s`) = %t; want %t", tc.pattern, complete, tc.isLiteral)
+		}
+		if str != tc.literal {
+			t.Errorf("LiteralPrefix(`%s`) = `%s`; want `%s`", tc.pattern, str, tc.literal)
+		}
+	}
+}
+
+type subexpIndex struct {
+	name  string
+	index int
+}
+
+type subexpCase struct {
+	input   string
+	num     int
+	names   []string
+	indices []subexpIndex
+}
+
+var emptySubexpIndices = []subexpIndex{{"", -1}, {"missing", -1}}
+
+var subexpCases = []subexpCase{
+	{``, 0, nil, emptySubexpIndices},
+	{`.*`, 0, nil, emptySubexpIndices},
+	{`abba`, 0, nil, emptySubexpIndices},
+	{`ab(b)a`, 1, []string{"", ""}, emptySubexpIndices},
+	{`ab(.*)a`, 1, []string{"", ""}, emptySubexpIndices},
+	{`(.*)ab(.*)a`, 2, []string{"", "", ""}, emptySubexpIndices},
+	{`(.*)(ab)(.*)a`, 3, []string{"", "", "", ""}, emptySubexpIndices},
+	{`(.*)((a)b)(.*)a`, 4, []string{"", "", "", "", ""}, emptySubexpIndices},
+	{`(.*)(\(ab)(.*)a`, 3, []string{"", "", "", ""}, emptySubexpIndices},
+	{`(.*)(\(a\)b)(.*)a`, 3, []string{"", "", "", ""}, emptySubexpIndices},
+	{`(?P<foo>.*)(?P<bar>(a)b)(?P<foo>.*)a`, 4, []string{"", "foo", "bar", "", "foo"}, []subexpIndex{{"", -1}, {"missing", -1}, {"foo", 1}, {"bar", 2}}},
+}
+
+func TestSubexp(t *testing.T) {
+	for _, c := range subexpCases {
+		re := MustCompile(c.input)
+		n := re.NumSubexp()
+		if n != c.num {
+			t.Errorf("%q: NumSubexp = %d, want %d", c.input, n, c.num)
+			continue
+		}
+		names := re.SubexpNames()
+		if len(names) != 1+n {
+			t.Errorf("%q: len(SubexpNames) = %d, want %d", c.input, len(names), n)
+			continue
+		}
+		if c.names != nil {
+			for i := 0; i < 1+n; i++ {
+				if names[i] != c.names[i] {
+					t.Errorf("%q: SubexpNames[%d] = %q, want %q", c.input, i, names[i], c.names[i])
+				}
+			}
+		}
+		for _, subexp := range c.indices {
+			index := re.SubexpIndex(subexp.name)
+			if index != subexp.index {
+				t.Errorf("%q: SubexpIndex(%q) = %d, want %d", c.input, subexp.name, index, subexp.index)
+			}
+		}
+	}
+}
+
+var splitTests = []struct {
+	s   string
+	r   string
+	n   int
+	out []string
+}{
+	{"foo:and:bar", ":", -1, []string{"foo", "and", "bar"}},
+	{"foo:and:bar", ":", 1, []string{"foo:and:bar"}},
+	{"foo:and:bar", ":", 2, []string{"foo", "and:bar"}},
+	{"foo:and:bar", "foo", -1, []string{"", ":and:bar"}},
+	{"foo:and:bar", "bar", -1, []string{"foo:and:", ""}},
+	{"foo:and:bar", "baz", -1, []string{"foo:and:bar"}},
+	{"baabaab", "a", -1, []string{"b", "", "b", "", "b"}},
+	{"baabaab", "a*", -1, []string{"b", "b", "b"}},
+	{"baabaab", "ba*", -1, []string{"", "", "", ""}},
+	{"foobar", "f*b*", -1, []string{"", "o", "o", "a", "r"}},
+	{"foobar", "f+.*b+", -1, []string{"", "ar"}},
+	{"foobooboar", "o{2}", -1, []string{"f", "b", "boar"}},
+	{"a,b,c,d,e,f", ",", 3, []string{"a", "b", "c,d,e,f"}},
+	{"a,b,c,d,e,f", ",", 0, nil},
+	{",", ",", -1, []string{"", ""}},
+	{",,,", ",", -1, []string{"", "", "", ""}},
+	{"", ",", -1, []string{""}},
+	{"", ".*", -1, []string{""}},
+	{"", ".+", -1, []string{""}},
+	{"", "", -1, []string{}},
+	{"foobar", "", -1, []string{"f", "o", "o", "b", "a", "r"}},
+	{"abaabaccadaaae", "a*", 5, []string{"", "b", "b", "c", "cadaaae"}},
+	{":x:y:z:", ":", -1, []string{"", "x", "y", "z", ""}},
+}
+
+func TestSplit(t *testing.T) {
+	for i, test := range splitTests {
+		re, err := Compile(test.r)
+		if err != nil {
+			t.Errorf("#%d: %q: compile error: %s", i, test.r, err.Error())
+			continue
+		}
+
+		split := re.Split(test.s, test.n)
+		if !reflect.DeepEqual(split, test.out) {
+			t.Errorf("#%d: %q: got %q; want %q", i, test.r, split, test.out)
+		}
+
+		if QuoteMeta(test.r) == test.r {
+			strsplit := strings.SplitN(test.s, test.r, test.n)
+			if !reflect.DeepEqual(split, strsplit) {
+				t.Errorf("#%d: Split(%q, %q, %d): regexp vs strings mismatch\nregexp=%q\nstrings=%q", i, test.s, test.r, test.n, split, strsplit)
+			}
+		}
+	}
+}
+
+// The following sequence of Match calls used to panic. See issue #12980.
+func TestParseAndCompile(t *testing.T) {
+	expr := "a$"
+	s := "a\nb"
+
+	for i, tc := range []struct {
+		reFlags  syntax.Flags
+		expMatch bool
+	}{
+		{syntax.Perl | syntax.OneLine, false},
+		{syntax.Perl &^ syntax.OneLine, true},
+	} {
+		parsed, err := syntax.Parse(expr, tc.reFlags)
+		if err != nil {
+			t.Fatalf("%d: parse: %v", i, err)
+		}
+		re, err := Compile(parsed.String())
+		if err != nil {
+			t.Fatalf("%d: compile: %v", i, err)
+		}
+		if match := re.MatchString(s); match != tc.expMatch {
+			t.Errorf("%d: %q.MatchString(%q)=%t; expected=%t", i, re, s, match, tc.expMatch)
+		}
+	}
+}
+
+// Check that one-pass cutoff does trigger.
+func TestOnePassCutoff(t *testing.T) {
+	re, err := syntax.Parse(`^x{1,1000}y{1,1000}$`, syntax.Perl)
+	if err != nil {
+		t.Fatalf("parse: %v", err)
+	}
+	p, err := syntax.Compile(re.Simplify())
+	if err != nil {
+		t.Fatalf("compile: %v", err)
+	}
+	if compileOnePass(p) != nil {
+		t.Fatalf("makeOnePass succeeded; wanted nil")
+	}
+}
+
+// Check that the same machine can be used with the standard matcher
+// and then the backtracker when there are no captures.
+func TestSwitchBacktrack(t *testing.T) {
+	re := MustCompile(`a|b`)
+	long := make([]byte, maxBacktrackVector+1)
+
+	// The following sequence of Match calls used to panic. See issue #10319.
+	re.Match(long)     // triggers standard matcher
+	re.Match(long[:1]) // triggers backtracker
+}
+
+func BenchmarkFind(b *testing.B) {
+	b.StopTimer()
+	re := MustCompile("a+b+")
+	wantSubs := "aaabb"
+	s := []byte("acbb" + wantSubs + "dd")
+	b.StartTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		subs := re.Find(s)
+		if string(subs) != wantSubs {
+			b.Fatalf("Find(%q) = %q; want %q", s, subs, wantSubs)
+		}
+	}
+}
+
+func BenchmarkFindAllNoMatches(b *testing.B) {
+	re := MustCompile("a+b+")
+	s := []byte("acddee")
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		all := re.FindAll(s, -1)
+		if all != nil {
+			b.Fatalf("FindAll(%q) = %q; want nil", s, all)
+		}
+	}
+}
+
+func BenchmarkFindString(b *testing.B) {
+	b.StopTimer()
+	re := MustCompile("a+b+")
+	wantSubs := "aaabb"
+	s := "acbb" + wantSubs + "dd"
+	b.StartTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		subs := re.FindString(s)
+		if subs != wantSubs {
+			b.Fatalf("FindString(%q) = %q; want %q", s, subs, wantSubs)
+		}
+	}
+}
+
+func BenchmarkFindSubmatch(b *testing.B) {
+	b.StopTimer()
+	re := MustCompile("a(a+b+)b")
+	wantSubs := "aaabb"
+	s := []byte("acbb" + wantSubs + "dd")
+	b.StartTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		subs := re.FindSubmatch(s)
+		if string(subs[0]) != wantSubs {
+			b.Fatalf("FindSubmatch(%q)[0] = %q; want %q", s, subs[0], wantSubs)
+		}
+		if string(subs[1]) != "aab" {
+			b.Fatalf("FindSubmatch(%q)[1] = %q; want %q", s, subs[1], "aab")
+		}
+	}
+}
+
+func BenchmarkFindStringSubmatch(b *testing.B) {
+	b.StopTimer()
+	re := MustCompile("a(a+b+)b")
+	wantSubs := "aaabb"
+	s := "acbb" + wantSubs + "dd"
+	b.StartTimer()
+	b.ReportAllocs()
+	for i := 0; i < b.N; i++ {
+		subs := re.FindStringSubmatch(s)
+		if subs[0] != wantSubs {
+			b.Fatalf("FindStringSubmatch(%q)[0] = %q; want %q", s, subs[0], wantSubs)
+		}
+		if subs[1] != "aab" {
+			b.Fatalf("FindStringSubmatch(%q)[1] = %q; want %q", s, subs[1], "aab")
+		}
+	}
+}
+
+func BenchmarkLiteral(b *testing.B) {
+	x := strings.Repeat("x", 50) + "y"
+	b.StopTimer()
+	re := MustCompile("y")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		if !re.MatchString(x) {
+			b.Fatalf("no match!")
+		}
+	}
+}
+
+func BenchmarkNotLiteral(b *testing.B) {
+	x := strings.Repeat("x", 50) + "y"
+	b.StopTimer()
+	re := MustCompile(".y")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		if !re.MatchString(x) {
+			b.Fatalf("no match!")
+		}
+	}
+}
+
+func BenchmarkMatchClass(b *testing.B) {
+	b.StopTimer()
+	x := strings.Repeat("xxxx", 20) + "w"
+	re := MustCompile("[abcdw]")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		if !re.MatchString(x) {
+			b.Fatalf("no match!")
+		}
+	}
+}
+
+func BenchmarkMatchClass_InRange(b *testing.B) {
+	b.StopTimer()
+	// 'b' is between 'a' and 'c', so the charclass
+	// range checking is no help here.
+	x := strings.Repeat("bbbb", 20) + "c"
+	re := MustCompile("[ac]")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		if !re.MatchString(x) {
+			b.Fatalf("no match!")
+		}
+	}
+}
+
+func BenchmarkReplaceAll(b *testing.B) {
+	x := "abcdefghijklmnopqrstuvwxyz"
+	b.StopTimer()
+	re := MustCompile("[cjrw]")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.ReplaceAllString(x, "")
+	}
+}
+
+func BenchmarkAnchoredLiteralShortNonMatch(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcdefghijklmnopqrstuvwxyz")
+	re := MustCompile("^zbc(d|e)")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkAnchoredLiteralLongNonMatch(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcdefghijklmnopqrstuvwxyz")
+	for i := 0; i < 15; i++ {
+		x = append(x, x...)
+	}
+	re := MustCompile("^zbc(d|e)")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkAnchoredShortMatch(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcdefghijklmnopqrstuvwxyz")
+	re := MustCompile("^.bc(d|e)")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkAnchoredLongMatch(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcdefghijklmnopqrstuvwxyz")
+	for i := 0; i < 15; i++ {
+		x = append(x, x...)
+	}
+	re := MustCompile("^.bc(d|e)")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkOnePassShortA(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcddddddeeeededd")
+	re := MustCompile("^.bc(d|e)*$")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkNotOnePassShortA(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcddddddeeeededd")
+	re := MustCompile(".bc(d|e)*$")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkOnePassShortB(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcddddddeeeededd")
+	re := MustCompile("^.bc(?:d|e)*$")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkNotOnePassShortB(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcddddddeeeededd")
+	re := MustCompile(".bc(?:d|e)*$")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkOnePassLongPrefix(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcdefghijklmnopqrstuvwxyz")
+	re := MustCompile("^abcdefghijklmnopqrstuvwxyz.*$")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkOnePassLongNotPrefix(b *testing.B) {
+	b.StopTimer()
+	x := []byte("abcdefghijklmnopqrstuvwxyz")
+	re := MustCompile("^.bcdefghijklmnopqrstuvwxyz.*$")
+	b.StartTimer()
+	for i := 0; i < b.N; i++ {
+		re.Match(x)
+	}
+}
+
+func BenchmarkMatchParallelShared(b *testing.B) {
+	x := []byte("this is a long line that contains foo bar baz")
+	re := MustCompile("foo (ba+r)? baz")
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			re.Match(x)
+		}
+	})
+}
+
+func BenchmarkMatchParallelCopied(b *testing.B) {
+	x := []byte("this is a long line that contains foo bar baz")
+	re := MustCompile("foo (ba+r)? baz")
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		re := re.Copy()
+		for pb.Next() {
+			re.Match(x)
+		}
+	})
+}
+
+var sink string
+
+func BenchmarkQuoteMetaAll(b *testing.B) {
+	specials := make([]byte, 0)
+	for i := byte(0); i < utf8.RuneSelf; i++ {
+		if special(i) {
+			specials = append(specials, i)
+		}
+	}
+	s := string(specials)
+	b.SetBytes(int64(len(s)))
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		sink = QuoteMeta(s)
+	}
+}
+
+func BenchmarkQuoteMetaNone(b *testing.B) {
+	s := "abcdefghijklmnopqrstuvwxyz"
+	b.SetBytes(int64(len(s)))
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		sink = QuoteMeta(s)
+	}
+}
+
+var compileBenchData = []struct{ name, re string }{
+	{"Onepass", `^a.[l-nA-Cg-j]?e$`},
+	{"Medium", `^((a|b|[d-z0-9])*(日){4,5}.)+$`},
+	{"Hard", strings.Repeat(`((abc)*|`, 50) + strings.Repeat(`)`, 50)},
+}
+
+func BenchmarkCompile(b *testing.B) {
+	for _, data := range compileBenchData {
+		b.Run(data.name, func(b *testing.B) {
+			b.ReportAllocs()
+			for i := 0; i < b.N; i++ {
+				if _, err := Compile(data.re); err != nil {
+					b.Fatal(err)
+				}
+			}
+		})
+	}
+}
+
+func TestDeepEqual(t *testing.T) {
+	re1 := MustCompile("a.*b.*c.*d")
+	re2 := MustCompile("a.*b.*c.*d")
+	if !reflect.DeepEqual(re1, re2) { // has always been true, since Go 1.
+		t.Errorf("DeepEqual(re1, re2) = false, want true")
+	}
+
+	re1.MatchString("abcdefghijklmn")
+	if !reflect.DeepEqual(re1, re2) {
+		t.Errorf("DeepEqual(re1, re2) = false, want true")
+	}
+
+	re2.MatchString("abcdefghijklmn")
+	if !reflect.DeepEqual(re1, re2) {
+		t.Errorf("DeepEqual(re1, re2) = false, want true")
+	}
+
+	re2.MatchString(strings.Repeat("abcdefghijklmn", 100))
+	if !reflect.DeepEqual(re1, re2) {
+		t.Errorf("DeepEqual(re1, re2) = false, want true")
+	}
+}
+
+var minInputLenTests = []struct {
+	Regexp string
+	min    int
+}{
+	{``, 0},
+	{`a`, 1},
+	{`aa`, 2},
+	{`(aa)a`, 3},
+	{`(?:aa)a`, 3},
+	{`a?a`, 1},
+	{`(aaa)|(aa)`, 2},
+	{`(aa)+a`, 3},
+	{`(aa)*a`, 1},
+	{`(aa){3,5}`, 6},
+	{`[a-z]`, 1},
+	{`日`, 3},
+}
+
+func TestMinInputLen(t *testing.T) {
+	for _, tt := range minInputLenTests {
+		re, _ := syntax.Parse(tt.Regexp, syntax.Perl)
+		m := minInputLen(re)
+		if m != tt.min {
+			t.Errorf("regexp %#q has minInputLen %d, should be %d", tt.Regexp, m, tt.min)
+		}
+	}
+}
+
+func TestUnmarshalText(t *testing.T) {
+	unmarshaled := new(Regexp)
+	for i := range goodRe {
+		re := compileTest(t, goodRe[i], "")
+		marshaled, err := re.MarshalText()
+		if err != nil {
+			t.Errorf("regexp %#q failed to marshal: %s", re, err)
+			continue
+		}
+		if err := unmarshaled.UnmarshalText(marshaled); err != nil {
+			t.Errorf("regexp %#q failed to unmarshal: %s", re, err)
+			continue
+		}
+		if unmarshaled.String() != goodRe[i] {
+			t.Errorf("UnmarshalText returned unexpected value: %s", unmarshaled.String())
+		}
+	}
+	t.Run("invalid pattern", func(t *testing.T) {
+		re := new(Regexp)
+		err := re.UnmarshalText([]byte(`\`))
+		if err == nil {
+			t.Error("unexpected success")
+		}
+	})
+}
diff --git a/src/regexp/backtrack.go b/src/regexp/backtrack.go
new file mode 100644
index 0000000..7c37c66
--- /dev/null
+++ b/src/regexp/backtrack.go
@@ -0,0 +1,365 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// backtrack is a regular expression search with submatch
+// tracking for small regular expressions and texts. It allocates
+// a bit vector with (length of input) * (length of prog) bits,
+// to make sure it never explores the same (character position, instruction)
+// state multiple times. This limits the search to run in time linear in
+// the length of the test.
+//
+// backtrack is a fast replacement for the NFA code on small
+// regexps when onepass cannot be used.
+
+package regexp
+
+import (
+	"regexp/syntax"
+	"sync"
+)
+
+// A job is an entry on the backtracker's job stack. It holds
+// the instruction pc and the position in the input.
+type job struct {
+	pc  uint32
+	arg bool
+	pos int
+}
+
+const (
+	visitedBits        = 32
+	maxBacktrackProg   = 500        // len(prog.Inst) <= max
+	maxBacktrackVector = 256 * 1024 // bit vector size <= max (bits)
+)
+
+// bitState holds state for the backtracker.
+type bitState struct {
+	end      int
+	cap      []int
+	matchcap []int
+	jobs     []job
+	visited  []uint32
+
+	inputs inputs
+}
+
+var bitStatePool sync.Pool
+
+func newBitState() *bitState {
+	b, ok := bitStatePool.Get().(*bitState)
+	if !ok {
+		b = new(bitState)
+	}
+	return b
+}
+
+func freeBitState(b *bitState) {
+	b.inputs.clear()
+	bitStatePool.Put(b)
+}
+
+// maxBitStateLen returns the maximum length of a string to search with
+// the backtracker using prog.
+func maxBitStateLen(prog *syntax.Prog) int {
+	if !shouldBacktrack(prog) {
+		return 0
+	}
+	return maxBacktrackVector / len(prog.Inst)
+}
+
+// shouldBacktrack reports whether the program is too
+// long for the backtracker to run.
+func shouldBacktrack(prog *syntax.Prog) bool {
+	return len(prog.Inst) <= maxBacktrackProg
+}
+
+// reset resets the state of the backtracker.
+// end is the end position in the input.
+// ncap is the number of captures.
+func (b *bitState) reset(prog *syntax.Prog, end int, ncap int) {
+	b.end = end
+
+	if cap(b.jobs) == 0 {
+		b.jobs = make([]job, 0, 256)
+	} else {
+		b.jobs = b.jobs[:0]
+	}
+
+	visitedSize := (len(prog.Inst)*(end+1) + visitedBits - 1) / visitedBits
+	if cap(b.visited) < visitedSize {
+		b.visited = make([]uint32, visitedSize, maxBacktrackVector/visitedBits)
+	} else {
+		b.visited = b.visited[:visitedSize]
+		clear(b.visited) // set to 0
+	}
+
+	if cap(b.cap) < ncap {
+		b.cap = make([]int, ncap)
+	} else {
+		b.cap = b.cap[:ncap]
+	}
+	for i := range b.cap {
+		b.cap[i] = -1
+	}
+
+	if cap(b.matchcap) < ncap {
+		b.matchcap = make([]int, ncap)
+	} else {
+		b.matchcap = b.matchcap[:ncap]
+	}
+	for i := range b.matchcap {
+		b.matchcap[i] = -1
+	}
+}
+
+// shouldVisit reports whether the combination of (pc, pos) has not
+// been visited yet.
+func (b *bitState) shouldVisit(pc uint32, pos int) bool {
+	n := uint(int(pc)*(b.end+1) + pos)
+	if b.visited[n/visitedBits]&(1<<(n&(visitedBits-1))) != 0 {
+		return false
+	}
+	b.visited[n/visitedBits] |= 1 << (n & (visitedBits - 1))
+	return true
+}
+
+// push pushes (pc, pos, arg) onto the job stack if it should be
+// visited.
+func (b *bitState) push(re *Regexp, pc uint32, pos int, arg bool) {
+	// Only check shouldVisit when arg is false.
+	// When arg is true, we are continuing a previous visit.
+	if re.prog.Inst[pc].Op != syntax.InstFail && (arg || b.shouldVisit(pc, pos)) {
+		b.jobs = append(b.jobs, job{pc: pc, arg: arg, pos: pos})
+	}
+}
+
+// tryBacktrack runs a backtracking search starting at pos.
+func (re *Regexp) tryBacktrack(b *bitState, i input, pc uint32, pos int) bool {
+	longest := re.longest
+
+	b.push(re, pc, pos, false)
+	for len(b.jobs) > 0 {
+		l := len(b.jobs) - 1
+		// Pop job off the stack.
+		pc := b.jobs[l].pc
+		pos := b.jobs[l].pos
+		arg := b.jobs[l].arg
+		b.jobs = b.jobs[:l]
+
+		// Optimization: rather than push and pop,
+		// code that is going to Push and continue
+		// the loop simply updates ip, p, and arg
+		// and jumps to CheckAndLoop. We have to
+		// do the ShouldVisit check that Push
+		// would have, but we avoid the stack
+		// manipulation.
+		goto Skip
+	CheckAndLoop:
+		if !b.shouldVisit(pc, pos) {
+			continue
+		}
+	Skip:
+
+		inst := &re.prog.Inst[pc]
+
+		switch inst.Op {
+		default:
+			panic("bad inst")
+		case syntax.InstFail:
+			panic("unexpected InstFail")
+		case syntax.InstAlt:
+			// Cannot just
+			//   b.push(inst.Out, pos, false)
+			//   b.push(inst.Arg, pos, false)
+			// If during the processing of inst.Out, we encounter
+			// inst.Arg via another path, we want to process it then.
+			// Pushing it here will inhibit that. Instead, re-push
+			// inst with arg==true as a reminder to push inst.Arg out
+			// later.
+			if arg {
+				// Finished inst.Out; try inst.Arg.
+				arg = false
+				pc = inst.Arg
+				goto CheckAndLoop
+			} else {
+				b.push(re, pc, pos, true)
+				pc = inst.Out
+				goto CheckAndLoop
+			}
+
+		case syntax.InstAltMatch:
+			// One opcode consumes runes; the other leads to match.
+			switch re.prog.Inst[inst.Out].Op {
+			case syntax.InstRune, syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
+				// inst.Arg is the match.
+				b.push(re, inst.Arg, pos, false)
+				pc = inst.Arg
+				pos = b.end
+				goto CheckAndLoop
+			}
+			// inst.Out is the match - non-greedy
+			b.push(re, inst.Out, b.end, false)
+			pc = inst.Out
+			goto CheckAndLoop
+
+		case syntax.InstRune:
+			r, width := i.step(pos)
+			if !inst.MatchRune(r) {
+				continue
+			}
+			pos += width
+			pc = inst.Out
+			goto CheckAndLoop
+
+		case syntax.InstRune1:
+			r, width := i.step(pos)
+			if r != inst.Rune[0] {
+				continue
+			}
+			pos += width
+			pc = inst.Out
+			goto CheckAndLoop
+
+		case syntax.InstRuneAnyNotNL:
+			r, width := i.step(pos)
+			if r == '\n' || r == endOfText {
+				continue
+			}
+			pos += width
+			pc = inst.Out
+			goto CheckAndLoop
+
+		case syntax.InstRuneAny:
+			r, width := i.step(pos)
+			if r == endOfText {
+				continue
+			}
+			pos += width
+			pc = inst.Out
+			goto CheckAndLoop
+
+		case syntax.InstCapture:
+			if arg {
+				// Finished inst.Out; restore the old value.
+				b.cap[inst.Arg] = pos
+				continue
+			} else {
+				if inst.Arg < uint32(len(b.cap)) {
+					// Capture pos to register, but save old value.
+					b.push(re, pc, b.cap[inst.Arg], true) // come back when we're done.
+					b.cap[inst.Arg] = pos
+				}
+				pc = inst.Out
+				goto CheckAndLoop
+			}
+
+		case syntax.InstEmptyWidth:
+			flag := i.context(pos)
+			if !flag.match(syntax.EmptyOp(inst.Arg)) {
+				continue
+			}
+			pc = inst.Out
+			goto CheckAndLoop
+
+		case syntax.InstNop:
+			pc = inst.Out
+			goto CheckAndLoop
+
+		case syntax.InstMatch:
+			// We found a match. If the caller doesn't care
+			// where the match is, no point going further.
+			if len(b.cap) == 0 {
+				return true
+			}
+
+			// Record best match so far.
+			// Only need to check end point, because this entire
+			// call is only considering one start position.
+			if len(b.cap) > 1 {
+				b.cap[1] = pos
+			}
+			if old := b.matchcap[1]; old == -1 || (longest && pos > 0 && pos > old) {
+				copy(b.matchcap, b.cap)
+			}
+
+			// If going for first match, we're done.
+			if !longest {
+				return true
+			}
+
+			// If we used the entire text, no longer match is possible.
+			if pos == b.end {
+				return true
+			}
+
+			// Otherwise, continue on in hope of a longer match.
+			continue
+		}
+	}
+
+	return longest && len(b.matchcap) > 1 && b.matchcap[1] >= 0
+}
+
+// backtrack runs a backtracking search of prog on the input starting at pos.
+func (re *Regexp) backtrack(ib []byte, is string, pos int, ncap int, dstCap []int) []int {
+	startCond := re.cond
+	if startCond == ^syntax.EmptyOp(0) { // impossible
+		return nil
+	}
+	if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
+		// Anchored match, past beginning of text.
+		return nil
+	}
+
+	b := newBitState()
+	i, end := b.inputs.init(nil, ib, is)
+	b.reset(re.prog, end, ncap)
+
+	// Anchored search must start at the beginning of the input
+	if startCond&syntax.EmptyBeginText != 0 {
+		if len(b.cap) > 0 {
+			b.cap[0] = pos
+		}
+		if !re.tryBacktrack(b, i, uint32(re.prog.Start), pos) {
+			freeBitState(b)
+			return nil
+		}
+	} else {
+
+		// Unanchored search, starting from each possible text position.
+		// Notice that we have to try the empty string at the end of
+		// the text, so the loop condition is pos <= end, not pos < end.
+		// This looks like it's quadratic in the size of the text,
+		// but we are not clearing visited between calls to TrySearch,
+		// so no work is duplicated and it ends up still being linear.
+		width := -1
+		for ; pos <= end && width != 0; pos += width {
+			if len(re.prefix) > 0 {
+				// Match requires literal prefix; fast search for it.
+				advance := i.index(re, pos)
+				if advance < 0 {
+					freeBitState(b)
+					return nil
+				}
+				pos += advance
+			}
+
+			if len(b.cap) > 0 {
+				b.cap[0] = pos
+			}
+			if re.tryBacktrack(b, i, uint32(re.prog.Start), pos) {
+				// Match must be leftmost; done.
+				goto Match
+			}
+			_, width = i.step(pos)
+		}
+		freeBitState(b)
+		return nil
+	}
+
+Match:
+	dstCap = append(dstCap, b.matchcap...)
+	freeBitState(b)
+	return dstCap
+}
diff --git a/src/regexp/example_test.go b/src/regexp/example_test.go
new file mode 100644
index 0000000..707445f
--- /dev/null
+++ b/src/regexp/example_test.go
@@ -0,0 +1,447 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package regexp_test
+
+import (
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+func Example() {
+	// Compile the expression once, usually at init time.
+	// Use raw strings to avoid having to quote the backslashes.
+	var validID = regexp.MustCompile(`^[a-z]+\[[0-9]+\]$`)
+
+	fmt.Println(validID.MatchString("adam[23]"))
+	fmt.Println(validID.MatchString("eve[7]"))
+	fmt.Println(validID.MatchString("Job[48]"))
+	fmt.Println(validID.MatchString("snakey"))
+	// Output:
+	// true
+	// true
+	// false
+	// false
+}
+
+func ExampleMatch() {
+	matched, err := regexp.Match(`foo.*`, []byte(`seafood`))
+	fmt.Println(matched, err)
+	matched, err = regexp.Match(`bar.*`, []byte(`seafood`))
+	fmt.Println(matched, err)
+	matched, err = regexp.Match(`a(b`, []byte(`seafood`))
+	fmt.Println(matched, err)
+
+	// Output:
+	// true <nil>
+	// false <nil>
+	// false error parsing regexp: missing closing ): `a(b`
+}
+
+func ExampleMatchString() {
+	matched, err := regexp.MatchString(`foo.*`, "seafood")
+	fmt.Println(matched, err)
+	matched, err = regexp.MatchString(`bar.*`, "seafood")
+	fmt.Println(matched, err)
+	matched, err = regexp.MatchString(`a(b`, "seafood")
+	fmt.Println(matched, err)
+	// Output:
+	// true <nil>
+	// false <nil>
+	// false error parsing regexp: missing closing ): `a(b`
+}
+
+func ExampleQuoteMeta() {
+	fmt.Println(regexp.QuoteMeta(`Escaping symbols like: .+*?()|[]{}^$`))
+	// Output:
+	// Escaping symbols like: \.\+\*\?\(\)\|\[\]\{\}\^\$
+}
+
+func ExampleRegexp_Find() {
+	re := regexp.MustCompile(`foo.?`)
+	fmt.Printf("%q\n", re.Find([]byte(`seafood fool`)))
+
+	// Output:
+	// "food"
+}
+
+func ExampleRegexp_FindAll() {
+	re := regexp.MustCompile(`foo.?`)
+	fmt.Printf("%q\n", re.FindAll([]byte(`seafood fool`), -1))
+
+	// Output:
+	// ["food" "fool"]
+}
+
+func ExampleRegexp_FindAllSubmatch() {
+	re := regexp.MustCompile(`foo(.?)`)
+	fmt.Printf("%q\n", re.FindAllSubmatch([]byte(`seafood fool`), -1))
+
+	// Output:
+	// [["food" "d"] ["fool" "l"]]
+}
+
+func ExampleRegexp_FindSubmatch() {
+	re := regexp.MustCompile(`foo(.?)`)
+	fmt.Printf("%q\n", re.FindSubmatch([]byte(`seafood fool`)))
+
+	// Output:
+	// ["food" "d"]
+}
+
+func ExampleRegexp_Match() {
+	re := regexp.MustCompile(`foo.?`)
+	fmt.Println(re.Match([]byte(`seafood fool`)))
+	fmt.Println(re.Match([]byte(`something else`)))
+
+	// Output:
+	// true
+	// false
+}
+
+func ExampleRegexp_FindString() {
+	re := regexp.MustCompile(`foo.?`)
+	fmt.Printf("%q\n", re.FindString("seafood fool"))
+	fmt.Printf("%q\n", re.FindString("meat"))
+	// Output:
+	// "food"
+	// ""
+}
+
+func ExampleRegexp_FindStringIndex() {
+	re := regexp.MustCompile(`ab?`)
+	fmt.Println(re.FindStringIndex("tablett"))
+	fmt.Println(re.FindStringIndex("foo") == nil)
+	// Output:
+	// [1 3]
+	// true
+}
+
+func ExampleRegexp_FindStringSubmatch() {
+	re := regexp.MustCompile(`a(x*)b(y|z)c`)
+	fmt.Printf("%q\n", re.FindStringSubmatch("-axxxbyc-"))
+	fmt.Printf("%q\n", re.FindStringSubmatch("-abzc-"))
+	// Output:
+	// ["axxxbyc" "xxx" "y"]
+	// ["abzc" "" "z"]
+}
+
+func ExampleRegexp_FindAllString() {
+	re := regexp.MustCompile(`a.`)
+	fmt.Println(re.FindAllString("paranormal", -1))
+	fmt.Println(re.FindAllString("paranormal", 2))
+	fmt.Println(re.FindAllString("graal", -1))
+	fmt.Println(re.FindAllString("none", -1))
+	// Output:
+	// [ar an al]
+	// [ar an]
+	// [aa]
+	// []
+}
+
+func ExampleRegexp_FindAllStringSubmatch() {
+	re := regexp.MustCompile(`a(x*)b`)
+	fmt.Printf("%q\n", re.FindAllStringSubmatch("-ab-", -1))
+	fmt.Printf("%q\n", re.FindAllStringSubmatch("-axxb-", -1))
+	fmt.Printf("%q\n", re.FindAllStringSubmatch("-ab-axb-", -1))
+	fmt.Printf("%q\n", re.FindAllStringSubmatch("-axxb-ab-", -1))
+	// Output:
+	// [["ab" ""]]
+	// [["axxb" "xx"]]
+	// [["ab" ""] ["axb" "x"]]
+	// [["axxb" "xx"] ["ab" ""]]
+}
+
+func ExampleRegexp_FindAllStringSubmatchIndex() {
+	re := regexp.MustCompile(`a(x*)b`)
+	// Indices:
+	//    01234567   012345678
+	//    -ab-axb-   -axxb-ab-
+	fmt.Println(re.FindAllStringSubmatchIndex("-ab-", -1))
+	fmt.Println(re.FindAllStringSubmatchIndex("-axxb-", -1))
+	fmt.Println(re.FindAllStringSubmatchIndex("-ab-axb-", -1))
+	fmt.Println(re.FindAllStringSubmatchIndex("-axxb-ab-", -1))
+	fmt.Println(re.FindAllStringSubmatchIndex("-foo-", -1))
+	// Output:
+	// [[1 3 2 2]]
+	// [[1 5 2 4]]
+	// [[1 3 2 2] [4 7 5 6]]
+	// [[1 5 2 4] [6 8 7 7]]
+	// []
+}
+
+func ExampleRegexp_FindSubmatchIndex() {
+	re := regexp.MustCompile(`a(x*)b`)
+	// Indices:
+	//    01234567   012345678
+	//    -ab-axb-   -axxb-ab-
+	fmt.Println(re.FindSubmatchIndex([]byte("-ab-")))
+	fmt.Println(re.FindSubmatchIndex([]byte("-axxb-")))
+	fmt.Println(re.FindSubmatchIndex([]byte("-ab-axb-")))
+	fmt.Println(re.FindSubmatchIndex([]byte("-axxb-ab-")))
+	fmt.Println(re.FindSubmatchIndex([]byte("-foo-")))
+	// Output:
+	// [1 3 2 2]
+	// [1 5 2 4]
+	// [1 3 2 2]
+	// [1 5 2 4]
+	// []
+}
+
+func ExampleRegexp_Longest() {
+	re := regexp.MustCompile(`a(|b)`)
+	fmt.Println(re.FindString("ab"))
+	re.Longest()
+	fmt.Println(re.FindString("ab"))
+	// Output:
+	// a
+	// ab
+}
+
+func ExampleRegexp_MatchString() {
+	re := regexp.MustCompile(`(gopher){2}`)
+	fmt.Println(re.MatchString("gopher"))
+	fmt.Println(re.MatchString("gophergopher"))
+	fmt.Println(re.MatchString("gophergophergopher"))
+	// Output:
+	// false
+	// true
+	// true
+}
+
+func ExampleRegexp_NumSubexp() {
+	re0 := regexp.MustCompile(`a.`)
+	fmt.Printf("%d\n", re0.NumSubexp())
+
+	re := regexp.MustCompile(`(.*)((a)b)(.*)a`)
+	fmt.Println(re.NumSubexp())
+	// Output:
+	// 0
+	// 4
+}
+
+func ExampleRegexp_ReplaceAll() {
+	re := regexp.MustCompile(`a(x*)b`)
+	fmt.Printf("%s\n", re.ReplaceAll([]byte("-ab-axxb-"), []byte("T")))
+	fmt.Printf("%s\n", re.ReplaceAll([]byte("-ab-axxb-"), []byte("$1")))
+	fmt.Printf("%s\n", re.ReplaceAll([]byte("-ab-axxb-"), []byte("$1W")))
+	fmt.Printf("%s\n", re.ReplaceAll([]byte("-ab-axxb-"), []byte("${1}W")))
+
+	re2 := regexp.MustCompile(`a(?P<1W>x*)b`)
+	fmt.Printf("%s\n", re2.ReplaceAll([]byte("-ab-axxb-"), []byte("$1W")))
+	fmt.Printf("%s\n", re2.ReplaceAll([]byte("-ab-axxb-"), []byte("${1}W")))
+
+	// Output:
+	// -T-T-
+	// --xx-
+	// ---
+	// -W-xxW-
+	// --xx-
+	// -W-xxW-
+}
+
+func ExampleRegexp_ReplaceAllLiteralString() {
+	re := regexp.MustCompile(`a(x*)b`)
+	fmt.Println(re.ReplaceAllLiteralString("-ab-axxb-", "T"))
+	fmt.Println(re.ReplaceAllLiteralString("-ab-axxb-", "$1"))
+	fmt.Println(re.ReplaceAllLiteralString("-ab-axxb-", "${1}"))
+	// Output:
+	// -T-T-
+	// -$1-$1-
+	// -${1}-${1}-
+}
+
+func ExampleRegexp_ReplaceAllString() {
+	re := regexp.MustCompile(`a(x*)b`)
+	fmt.Println(re.ReplaceAllString("-ab-axxb-", "T"))
+	fmt.Println(re.ReplaceAllString("-ab-axxb-", "$1"))
+	fmt.Println(re.ReplaceAllString("-ab-axxb-", "$1W"))
+	fmt.Println(re.ReplaceAllString("-ab-axxb-", "${1}W"))
+
+	re2 := regexp.MustCompile(`a(?P<1W>x*)b`)
+	fmt.Printf("%s\n", re2.ReplaceAllString("-ab-axxb-", "$1W"))
+	fmt.Println(re.ReplaceAllString("-ab-axxb-", "${1}W"))
+
+	// Output:
+	// -T-T-
+	// --xx-
+	// ---
+	// -W-xxW-
+	// --xx-
+	// -W-xxW-
+}
+
+func ExampleRegexp_ReplaceAllStringFunc() {
+	re := regexp.MustCompile(`[^aeiou]`)
+	fmt.Println(re.ReplaceAllStringFunc("seafood fool", strings.ToUpper))
+	// Output:
+	// SeaFooD FooL
+}
+
+func ExampleRegexp_SubexpNames() {
+	re := regexp.MustCompile(`(?P<first>[a-zA-Z]+) (?P<last>[a-zA-Z]+)`)
+	fmt.Println(re.MatchString("Alan Turing"))
+	fmt.Printf("%q\n", re.SubexpNames())
+	reversed := fmt.Sprintf("${%s} ${%s}", re.SubexpNames()[2], re.SubexpNames()[1])
+	fmt.Println(reversed)
+	fmt.Println(re.ReplaceAllString("Alan Turing", reversed))
+	// Output:
+	// true
+	// ["" "first" "last"]
+	// ${last} ${first}
+	// Turing Alan
+}
+
+func ExampleRegexp_SubexpIndex() {
+	re := regexp.MustCompile(`(?P<first>[a-zA-Z]+) (?P<last>[a-zA-Z]+)`)
+	fmt.Println(re.MatchString("Alan Turing"))
+	matches := re.FindStringSubmatch("Alan Turing")
+	lastIndex := re.SubexpIndex("last")
+	fmt.Printf("last => %d\n", lastIndex)
+	fmt.Println(matches[lastIndex])
+	// Output:
+	// true
+	// last => 2
+	// Turing
+}
+
+func ExampleRegexp_Split() {
+	a := regexp.MustCompile(`a`)
+	fmt.Println(a.Split("banana", -1))
+	fmt.Println(a.Split("banana", 0))
+	fmt.Println(a.Split("banana", 1))
+	fmt.Println(a.Split("banana", 2))
+	zp := regexp.MustCompile(`z+`)
+	fmt.Println(zp.Split("pizza", -1))
+	fmt.Println(zp.Split("pizza", 0))
+	fmt.Println(zp.Split("pizza", 1))
+	fmt.Println(zp.Split("pizza", 2))
+	// Output:
+	// [b n n ]
+	// []
+	// [banana]
+	// [b nana]
+	// [pi a]
+	// []
+	// [pizza]
+	// [pi a]
+}
+
+func ExampleRegexp_Expand() {
+	content := []byte(`
+	# comment line
+	option1: value1
+	option2: value2
+
+	# another comment line
+	option3: value3
+`)
+
+	// Regex pattern captures "key: value" pair from the content.
+	pattern := regexp.MustCompile(`(?m)(?P<key>\w+):\s+(?P<value>\w+)$`)
+
+	// Template to convert "key: value" to "key=value" by
+	// referencing the values captured by the regex pattern.
+	template := []byte("$key=$value\n")
+
+	result := []byte{}
+
+	// For each match of the regex in the content.
+	for _, submatches := range pattern.FindAllSubmatchIndex(content, -1) {
+		// Apply the captured submatches to the template and append the output
+		// to the result.
+		result = pattern.Expand(result, template, content, submatches)
+	}
+	fmt.Println(string(result))
+	// Output:
+	// option1=value1
+	// option2=value2
+	// option3=value3
+}
+
+func ExampleRegexp_ExpandString() {
+	content := `
+	# comment line
+	option1: value1
+	option2: value2
+
+	# another comment line
+	option3: value3
+`
+
+	// Regex pattern captures "key: value" pair from the content.
+	pattern := regexp.MustCompile(`(?m)(?P<key>\w+):\s+(?P<value>\w+)$`)
+
+	// Template to convert "key: value" to "key=value" by
+	// referencing the values captured by the regex pattern.
+	template := "$key=$value\n"
+
+	result := []byte{}
+
+	// For each match of the regex in the content.
+	for _, submatches := range pattern.FindAllStringSubmatchIndex(content, -1) {
+		// Apply the captured submatches to the template and append the output
+		// to the result.
+		result = pattern.ExpandString(result, template, content, submatches)
+	}
+	fmt.Println(string(result))
+	// Output:
+	// option1=value1
+	// option2=value2
+	// option3=value3
+}
+
+func ExampleRegexp_FindIndex() {
+	content := []byte(`
+	# comment line
+	option1: value1
+	option2: value2
+`)
+	// Regex pattern captures "key: value" pair from the content.
+	pattern := regexp.MustCompile(`(?m)(?P<key>\w+):\s+(?P<value>\w+)$`)
+
+	loc := pattern.FindIndex(content)
+	fmt.Println(loc)
+	fmt.Println(string(content[loc[0]:loc[1]]))
+	// Output:
+	// [18 33]
+	// option1: value1
+}
+
+func ExampleRegexp_FindAllSubmatchIndex() {
+	content := []byte(`
+	# comment line
+	option1: value1
+	option2: value2
+`)
+	// Regex pattern captures "key: value" pair from the content.
+	pattern := regexp.MustCompile(`(?m)(?P<key>\w+):\s+(?P<value>\w+)$`)
+	allIndexes := pattern.FindAllSubmatchIndex(content, -1)
+	for _, loc := range allIndexes {
+		fmt.Println(loc)
+		fmt.Println(string(content[loc[0]:loc[1]]))
+		fmt.Println(string(content[loc[2]:loc[3]]))
+		fmt.Println(string(content[loc[4]:loc[5]]))
+	}
+	// Output:
+	// [18 33 18 25 27 33]
+	// option1: value1
+	// option1
+	// value1
+	// [35 50 35 42 44 50]
+	// option2: value2
+	// option2
+	// value2
+}
+
+func ExampleRegexp_FindAllIndex() {
+	content := []byte("London")
+	re := regexp.MustCompile(`o.`)
+	fmt.Println(re.FindAllIndex(content, 1))
+	fmt.Println(re.FindAllIndex(content, -1))
+	// Output:
+	// [[1 3]]
+	// [[1 3] [4 6]]
+}
diff --git a/src/regexp/exec.go b/src/regexp/exec.go
new file mode 100644
index 0000000..3fc4b68
--- /dev/null
+++ b/src/regexp/exec.go
@@ -0,0 +1,554 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package regexp
+
+import (
+	"io"
+	"regexp/syntax"
+	"sync"
+)
+
+// A queue is a 'sparse array' holding pending threads of execution.
+// See https://research.swtch.com/2008/03/using-uninitialized-memory-for-fun-and.html
+type queue struct {
+	sparse []uint32
+	dense  []entry
+}
+
+// An entry is an entry on a queue.
+// It holds both the instruction pc and the actual thread.
+// Some queue entries are just place holders so that the machine
+// knows it has considered that pc. Such entries have t == nil.
+type entry struct {
+	pc uint32
+	t  *thread
+}
+
+// A thread is the state of a single path through the machine:
+// an instruction and a corresponding capture array.
+// See https://swtch.com/~rsc/regexp/regexp2.html
+type thread struct {
+	inst *syntax.Inst
+	cap  []int
+}
+
+// A machine holds all the state during an NFA simulation for p.
+type machine struct {
+	re       *Regexp      // corresponding Regexp
+	p        *syntax.Prog // compiled program
+	q0, q1   queue        // two queues for runq, nextq
+	pool     []*thread    // pool of available threads
+	matched  bool         // whether a match was found
+	matchcap []int        // capture information for the match
+
+	inputs inputs
+}
+
+type inputs struct {
+	// cached inputs, to avoid allocation
+	bytes  inputBytes
+	string inputString
+	reader inputReader
+}
+
+func (i *inputs) newBytes(b []byte) input {
+	i.bytes.str = b
+	return &i.bytes
+}
+
+func (i *inputs) newString(s string) input {
+	i.string.str = s
+	return &i.string
+}
+
+func (i *inputs) newReader(r io.RuneReader) input {
+	i.reader.r = r
+	i.reader.atEOT = false
+	i.reader.pos = 0
+	return &i.reader
+}
+
+func (i *inputs) clear() {
+	// We need to clear 1 of these.
+	// Avoid the expense of clearing the others (pointer write barrier).
+	if i.bytes.str != nil {
+		i.bytes.str = nil
+	} else if i.reader.r != nil {
+		i.reader.r = nil
+	} else {
+		i.string.str = ""
+	}
+}
+
+func (i *inputs) init(r io.RuneReader, b []byte, s string) (input, int) {
+	if r != nil {
+		return i.newReader(r), 0
+	}
+	if b != nil {
+		return i.newBytes(b), len(b)
+	}
+	return i.newString(s), len(s)
+}
+
+func (m *machine) init(ncap int) {
+	for _, t := range m.pool {
+		t.cap = t.cap[:ncap]
+	}
+	m.matchcap = m.matchcap[:ncap]
+}
+
+// alloc allocates a new thread with the given instruction.
+// It uses the free pool if possible.
+func (m *machine) alloc(i *syntax.Inst) *thread {
+	var t *thread
+	if n := len(m.pool); n > 0 {
+		t = m.pool[n-1]
+		m.pool = m.pool[:n-1]
+	} else {
+		t = new(thread)
+		t.cap = make([]int, len(m.matchcap), cap(m.matchcap))
+	}
+	t.inst = i
+	return t
+}
+
+// A lazyFlag is a lazily-evaluated syntax.EmptyOp,
+// for checking zero-width flags like ^ $ \A \z \B \b.
+// It records the pair of relevant runes and does not
+// determine the implied flags until absolutely necessary
+// (most of the time, that means never).
+type lazyFlag uint64
+
+func newLazyFlag(r1, r2 rune) lazyFlag {
+	return lazyFlag(uint64(r1)<<32 | uint64(uint32(r2)))
+}
+
+func (f lazyFlag) match(op syntax.EmptyOp) bool {
+	if op == 0 {
+		return true
+	}
+	r1 := rune(f >> 32)
+	if op&syntax.EmptyBeginLine != 0 {
+		if r1 != '\n' && r1 >= 0 {
+			return false
+		}
+		op &^= syntax.EmptyBeginLine
+	}
+	if op&syntax.EmptyBeginText != 0 {
+		if r1 >= 0 {
+			return false
+		}
+		op &^= syntax.EmptyBeginText
+	}
+	if op == 0 {
+		return true
+	}
+	r2 := rune(f)
+	if op&syntax.EmptyEndLine != 0 {
+		if r2 != '\n' && r2 >= 0 {
+			return false
+		}
+		op &^= syntax.EmptyEndLine
+	}
+	if op&syntax.EmptyEndText != 0 {
+		if r2 >= 0 {
+			return false
+		}
+		op &^= syntax.EmptyEndText
+	}
+	if op == 0 {
+		return true
+	}
+	if syntax.IsWordChar(r1) != syntax.IsWordChar(r2) {
+		op &^= syntax.EmptyWordBoundary
+	} else {
+		op &^= syntax.EmptyNoWordBoundary
+	}
+	return op == 0
+}
+
+// match runs the machine over the input starting at pos.
+// It reports whether a match was found.
+// If so, m.matchcap holds the submatch information.
+func (m *machine) match(i input, pos int) bool {
+	startCond := m.re.cond
+	if startCond == ^syntax.EmptyOp(0) { // impossible
+		return false
+	}
+	m.matched = false
+	for i := range m.matchcap {
+		m.matchcap[i] = -1
+	}
+	runq, nextq := &m.q0, &m.q1
+	r, r1 := endOfText, endOfText
+	width, width1 := 0, 0
+	r, width = i.step(pos)
+	if r != endOfText {
+		r1, width1 = i.step(pos + width)
+	}
+	var flag lazyFlag
+	if pos == 0 {
+		flag = newLazyFlag(-1, r)
+	} else {
+		flag = i.context(pos)
+	}
+	for {
+		if len(runq.dense) == 0 {
+			if startCond&syntax.EmptyBeginText != 0 && pos != 0 {
+				// Anchored match, past beginning of text.
+				break
+			}
+			if m.matched {
+				// Have match; finished exploring alternatives.
+				break
+			}
+			if len(m.re.prefix) > 0 && r1 != m.re.prefixRune && i.canCheckPrefix() {
+				// Match requires literal prefix; fast search for it.
+				advance := i.index(m.re, pos)
+				if advance < 0 {
+					break
+				}
+				pos += advance
+				r, width = i.step(pos)
+				r1, width1 = i.step(pos + width)
+			}
+		}
+		if !m.matched {
+			if len(m.matchcap) > 0 {
+				m.matchcap[0] = pos
+			}
+			m.add(runq, uint32(m.p.Start), pos, m.matchcap, &flag, nil)
+		}
+		flag = newLazyFlag(r, r1)
+		m.step(runq, nextq, pos, pos+width, r, &flag)
+		if width == 0 {
+			break
+		}
+		if len(m.matchcap) == 0 && m.matched {
+			// Found a match and not paying attention
+			// to where it is, so any match will do.
+			break
+		}
+		pos += width
+		r, width = r1, width1
+		if r != endOfText {
+			r1, width1 = i.step(pos + width)
+		}
+		runq, nextq = nextq, runq
+	}
+	m.clear(nextq)
+	return m.matched
+}
+
+// clear frees all threads on the thread queue.
+func (m *machine) clear(q *queue) {
+	for _, d := range q.dense {
+		if d.t != nil {
+			m.pool = append(m.pool, d.t)
+		}
+	}
+	q.dense = q.dense[:0]
+}
+
+// step executes one step of the machine, running each of the threads
+// on runq and appending new threads to nextq.
+// The step processes the rune c (which may be endOfText),
+// which starts at position pos and ends at nextPos.
+// nextCond gives the setting for the empty-width flags after c.
+func (m *machine) step(runq, nextq *queue, pos, nextPos int, c rune, nextCond *lazyFlag) {
+	longest := m.re.longest
+	for j := 0; j < len(runq.dense); j++ {
+		d := &runq.dense[j]
+		t := d.t
+		if t == nil {
+			continue
+		}
+		if longest && m.matched && len(t.cap) > 0 && m.matchcap[0] < t.cap[0] {
+			m.pool = append(m.pool, t)
+			continue
+		}
+		i := t.inst
+		add := false
+		switch i.Op {
+		default:
+			panic("bad inst")
+
+		case syntax.InstMatch:
+			if len(t.cap) > 0 && (!longest || !m.matched || m.matchcap[1] < pos) {
+				t.cap[1] = pos
+				copy(m.matchcap, t.cap)
+			}
+			if !longest {
+				// First-match mode: cut off all lower-priority threads.
+				for _, d := range runq.dense[j+1:] {
+					if d.t != nil {
+						m.pool = append(m.pool, d.t)
+					}
+				}
+				runq.dense = runq.dense[:0]
+			}
+			m.matched = true
+
+		case syntax.InstRune:
+			add = i.MatchRune(c)
+		case syntax.InstRune1:
+			add = c == i.Rune[0]
+		case syntax.InstRuneAny:
+			add = true
+		case syntax.InstRuneAnyNotNL:
+			add = c != '\n'
+		}
+		if add {
+			t = m.add(nextq, i.Out, nextPos, t.cap, nextCond, t)
+		}
+		if t != nil {
+			m.pool = append(m.pool, t)
+		}
+	}
+	runq.dense = runq.dense[:0]
+}
+
+// add adds an entry to q for pc, unless the q already has such an entry.
+// It also recursively adds an entry for all instructions reachable from pc by following
+// empty-width conditions satisfied by cond.  pos gives the current position
+// in the input.
+func (m *machine) add(q *queue, pc uint32, pos int, cap []int, cond *lazyFlag, t *thread) *thread {
+Again:
+	if pc == 0 {
+		return t
+	}
+	if j := q.sparse[pc]; j < uint32(len(q.dense)) && q.dense[j].pc == pc {
+		return t
+	}
+
+	j := len(q.dense)
+	q.dense = q.dense[:j+1]
+	d := &q.dense[j]
+	d.t = nil
+	d.pc = pc
+	q.sparse[pc] = uint32(j)
+
+	i := &m.p.Inst[pc]
+	switch i.Op {
+	default:
+		panic("unhandled")
+	case syntax.InstFail:
+		// nothing
+	case syntax.InstAlt, syntax.InstAltMatch:
+		t = m.add(q, i.Out, pos, cap, cond, t)
+		pc = i.Arg
+		goto Again
+	case syntax.InstEmptyWidth:
+		if cond.match(syntax.EmptyOp(i.Arg)) {
+			pc = i.Out
+			goto Again
+		}
+	case syntax.InstNop:
+		pc = i.Out
+		goto Again
+	case syntax.InstCapture:
+		if int(i.Arg) < len(cap) {
+			opos := cap[i.Arg]
+			cap[i.Arg] = pos
+			m.add(q, i.Out, pos, cap, cond, nil)
+			cap[i.Arg] = opos
+		} else {
+			pc = i.Out
+			goto Again
+		}
+	case syntax.InstMatch, syntax.InstRune, syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
+		if t == nil {
+			t = m.alloc(i)
+		} else {
+			t.inst = i
+		}
+		if len(cap) > 0 && &t.cap[0] != &cap[0] {
+			copy(t.cap, cap)
+		}
+		d.t = t
+		t = nil
+	}
+	return t
+}
+
+type onePassMachine struct {
+	inputs   inputs
+	matchcap []int
+}
+
+var onePassPool sync.Pool
+
+func newOnePassMachine() *onePassMachine {
+	m, ok := onePassPool.Get().(*onePassMachine)
+	if !ok {
+		m = new(onePassMachine)
+	}
+	return m
+}
+
+func freeOnePassMachine(m *onePassMachine) {
+	m.inputs.clear()
+	onePassPool.Put(m)
+}
+
+// doOnePass implements r.doExecute using the one-pass execution engine.
+func (re *Regexp) doOnePass(ir io.RuneReader, ib []byte, is string, pos, ncap int, dstCap []int) []int {
+	startCond := re.cond
+	if startCond == ^syntax.EmptyOp(0) { // impossible
+		return nil
+	}
+
+	m := newOnePassMachine()
+	if cap(m.matchcap) < ncap {
+		m.matchcap = make([]int, ncap)
+	} else {
+		m.matchcap = m.matchcap[:ncap]
+	}
+
+	matched := false
+	for i := range m.matchcap {
+		m.matchcap[i] = -1
+	}
+
+	i, _ := m.inputs.init(ir, ib, is)
+
+	r, r1 := endOfText, endOfText
+	width, width1 := 0, 0
+	r, width = i.step(pos)
+	if r != endOfText {
+		r1, width1 = i.step(pos + width)
+	}
+	var flag lazyFlag
+	if pos == 0 {
+		flag = newLazyFlag(-1, r)
+	} else {
+		flag = i.context(pos)
+	}
+	pc := re.onepass.Start
+	inst := &re.onepass.Inst[pc]
+	// If there is a simple literal prefix, skip over it.
+	if pos == 0 && flag.match(syntax.EmptyOp(inst.Arg)) &&
+		len(re.prefix) > 0 && i.canCheckPrefix() {
+		// Match requires literal prefix; fast search for it.
+		if !i.hasPrefix(re) {
+			goto Return
+		}
+		pos += len(re.prefix)
+		r, width = i.step(pos)
+		r1, width1 = i.step(pos + width)
+		flag = i.context(pos)
+		pc = int(re.prefixEnd)
+	}
+	for {
+		inst = &re.onepass.Inst[pc]
+		pc = int(inst.Out)
+		switch inst.Op {
+		default:
+			panic("bad inst")
+		case syntax.InstMatch:
+			matched = true
+			if len(m.matchcap) > 0 {
+				m.matchcap[0] = 0
+				m.matchcap[1] = pos
+			}
+			goto Return
+		case syntax.InstRune:
+			if !inst.MatchRune(r) {
+				goto Return
+			}
+		case syntax.InstRune1:
+			if r != inst.Rune[0] {
+				goto Return
+			}
+		case syntax.InstRuneAny:
+			// Nothing
+		case syntax.InstRuneAnyNotNL:
+			if r == '\n' {
+				goto Return
+			}
+		// peek at the input rune to see which branch of the Alt to take
+		case syntax.InstAlt, syntax.InstAltMatch:
+			pc = int(onePassNext(inst, r))
+			continue
+		case syntax.InstFail:
+			goto Return
+		case syntax.InstNop:
+			continue
+		case syntax.InstEmptyWidth:
+			if !flag.match(syntax.EmptyOp(inst.Arg)) {
+				goto Return
+			}
+			continue
+		case syntax.InstCapture:
+			if int(inst.Arg) < len(m.matchcap) {
+				m.matchcap[inst.Arg] = pos
+			}
+			continue
+		}
+		if width == 0 {
+			break
+		}
+		flag = newLazyFlag(r, r1)
+		pos += width
+		r, width = r1, width1
+		if r != endOfText {
+			r1, width1 = i.step(pos + width)
+		}
+	}
+
+Return:
+	if !matched {
+		freeOnePassMachine(m)
+		return nil
+	}
+
+	dstCap = append(dstCap, m.matchcap...)
+	freeOnePassMachine(m)
+	return dstCap
+}
+
+// doMatch reports whether either r, b or s match the regexp.
+func (re *Regexp) doMatch(r io.RuneReader, b []byte, s string) bool {
+	return re.doExecute(r, b, s, 0, 0, nil) != nil
+}
+
+// doExecute finds the leftmost match in the input, appends the position
+// of its subexpressions to dstCap and returns dstCap.
+//
+// nil is returned if no matches are found and non-nil if matches are found.
+func (re *Regexp) doExecute(r io.RuneReader, b []byte, s string, pos int, ncap int, dstCap []int) []int {
+	if dstCap == nil {
+		// Make sure 'return dstCap' is non-nil.
+		dstCap = arrayNoInts[:0:0]
+	}
+
+	if r == nil && len(b)+len(s) < re.minInputLen {
+		return nil
+	}
+
+	if re.onepass != nil {
+		return re.doOnePass(r, b, s, pos, ncap, dstCap)
+	}
+	if r == nil && len(b)+len(s) < re.maxBitStateLen {
+		return re.backtrack(b, s, pos, ncap, dstCap)
+	}
+
+	m := re.get()
+	i, _ := m.inputs.init(r, b, s)
+
+	m.init(ncap)
+	if !m.match(i, pos) {
+		re.put(m)
+		return nil
+	}
+
+	dstCap = append(dstCap, m.matchcap...)
+	re.put(m)
+	return dstCap
+}
+
+// arrayNoInts is returned by doExecute match if nil dstCap is passed
+// to it with ncap=0.
+var arrayNoInts [0]int
diff --git a/src/regexp/exec2_test.go b/src/regexp/exec2_test.go
new file mode 100644
index 0000000..b6dac4a
--- /dev/null
+++ b/src/regexp/exec2_test.go
@@ -0,0 +1,20 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !race
+
+package regexp
+
+import (
+	"testing"
+)
+
+// This test is excluded when running under the race detector because
+// it is a very expensive test and takes too long.
+func TestRE2Exhaustive(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping TestRE2Exhaustive during short test")
+	}
+	testRE2(t, "testdata/re2-exhaustive.txt.bz2")
+}
diff --git a/src/regexp/exec_test.go b/src/regexp/exec_test.go
new file mode 100644
index 0000000..1694230
--- /dev/null
+++ b/src/regexp/exec_test.go
@@ -0,0 +1,747 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package regexp
+
+import (
+	"bufio"
+	"compress/bzip2"
+	"fmt"
+	"internal/testenv"
+	"io"
+	"os"
+	"path/filepath"
+	"regexp/syntax"
+	"strconv"
+	"strings"
+	"testing"
+	"unicode/utf8"
+)
+
+// TestRE2 tests this package's regexp API against test cases
+// considered during RE2's exhaustive tests, which run all possible
+// regexps over a given set of atoms and operators, up to a given
+// complexity, over all possible strings over a given alphabet,
+// up to a given size. Rather than try to link with RE2, we read a
+// log file containing the test cases and the expected matches.
+// The log file, re2-exhaustive.txt, is generated by running 'make log'
+// in the open source RE2 distribution https://github.com/google/re2/.
+//
+// The test file format is a sequence of stanzas like:
+//
+//	strings
+//	"abc"
+//	"123x"
+//	regexps
+//	"[a-z]+"
+//	0-3;0-3
+//	-;-
+//	"([0-9])([0-9])([0-9])"
+//	-;-
+//	-;0-3 0-1 1-2 2-3
+//
+// The stanza begins by defining a set of strings, quoted
+// using Go double-quote syntax, one per line. Then the
+// regexps section gives a sequence of regexps to run on
+// the strings. In the block that follows a regexp, each line
+// gives the semicolon-separated match results of running
+// the regexp on the corresponding string.
+// Each match result is either a single -, meaning no match, or a
+// space-separated sequence of pairs giving the match and
+// submatch indices. An unmatched subexpression formats
+// its pair as a single - (not illustrated above).  For now
+// each regexp run produces two match results, one for a
+// “full match” that restricts the regexp to matching the entire
+// string or nothing, and one for a “partial match” that gives
+// the leftmost first match found in the string.
+//
+// Lines beginning with # are comments. Lines beginning with
+// a capital letter are test names printed during RE2's test suite
+// and are echoed into t but otherwise ignored.
+//
+// At time of writing, re2-exhaustive.txt is 59 MB but compresses to 385 kB,
+// so we store re2-exhaustive.txt.bz2 in the repository and decompress it on the fly.
+func TestRE2Search(t *testing.T) {
+	testRE2(t, "testdata/re2-search.txt")
+}
+
+func testRE2(t *testing.T, file string) {
+	f, err := os.Open(file)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer f.Close()
+	var txt io.Reader
+	if strings.HasSuffix(file, ".bz2") {
+		z := bzip2.NewReader(f)
+		txt = z
+		file = file[:len(file)-len(".bz2")] // for error messages
+	} else {
+		txt = f
+	}
+	lineno := 0
+	scanner := bufio.NewScanner(txt)
+	var (
+		str       []string
+		input     []string
+		inStrings bool
+		re        *Regexp
+		refull    *Regexp
+		nfail     int
+		ncase     int
+	)
+	for lineno := 1; scanner.Scan(); lineno++ {
+		line := scanner.Text()
+		switch {
+		case line == "":
+			t.Fatalf("%s:%d: unexpected blank line", file, lineno)
+		case line[0] == '#':
+			continue
+		case 'A' <= line[0] && line[0] <= 'Z':
+			// Test name.
+			t.Logf("%s\n", line)
+			continue
+		case line == "strings":
+			str = str[:0]
+			inStrings = true
+		case line == "regexps":
+			inStrings = false
+		case line[0] == '"':
+			q, err := strconv.Unquote(line)
+			if err != nil {
+				// Fatal because we'll get out of sync.
+				t.Fatalf("%s:%d: unquote %s: %v", file, lineno, line, err)
+			}
+			if inStrings {
+				str = append(str, q)
+				continue
+			}
+			// Is a regexp.
+			if len(input) != 0 {
+				t.Fatalf("%s:%d: out of sync: have %d strings left before %#q", file, lineno, len(input), q)
+			}
+			re, err = tryCompile(q)
+			if err != nil {
+				if err.Error() == "error parsing regexp: invalid escape sequence: `\\C`" {
+					// We don't and likely never will support \C; keep going.
+					continue
+				}
+				t.Errorf("%s:%d: compile %#q: %v", file, lineno, q, err)
+				if nfail++; nfail >= 100 {
+					t.Fatalf("stopping after %d errors", nfail)
+				}
+				continue
+			}
+			full := `\A(?:` + q + `)\z`
+			refull, err = tryCompile(full)
+			if err != nil {
+				// Fatal because q worked, so this should always work.
+				t.Fatalf("%s:%d: compile full %#q: %v", file, lineno, full, err)
+			}
+			input = str
+		case line[0] == '-' || '0' <= line[0] && line[0] <= '9':
+			// A sequence of match results.
+			ncase++
+			if re == nil {
+				// Failed to compile: skip results.
+				continue
+			}
+			if len(input) == 0 {
+				t.Fatalf("%s:%d: out of sync: no input remaining", file, lineno)
+			}
+			var text string
+			text, input = input[0], input[1:]
+			if !isSingleBytes(text) && strings.Contains(re.String(), `\B`) {
+				// RE2's \B considers every byte position,
+				// so it sees 'not word boundary' in the
+				// middle of UTF-8 sequences. This package
+				// only considers the positions between runes,
+				// so it disagrees. Skip those cases.
+				continue
+			}
+			res := strings.Split(line, ";")
+			if len(res) != len(run) {
+				t.Fatalf("%s:%d: have %d test results, want %d", file, lineno, len(res), len(run))
+			}
+			for i := range res {
+				have, suffix := run[i](re, refull, text)
+				want := parseResult(t, file, lineno, res[i])
+				if !same(have, want) {
+					t.Errorf("%s:%d: %#q%s.FindSubmatchIndex(%#q) = %v, want %v", file, lineno, re, suffix, text, have, want)
+					if nfail++; nfail >= 100 {
+						t.Fatalf("stopping after %d errors", nfail)
+					}
+					continue
+				}
+				b, suffix := match[i](re, refull, text)
+				if b != (want != nil) {
+					t.Errorf("%s:%d: %#q%s.MatchString(%#q) = %v, want %v", file, lineno, re, suffix, text, b, !b)
+					if nfail++; nfail >= 100 {
+						t.Fatalf("stopping after %d errors", nfail)
+					}
+					continue
+				}
+			}
+
+		default:
+			t.Fatalf("%s:%d: out of sync: %s\n", file, lineno, line)
+		}
+	}
+	if err := scanner.Err(); err != nil {
+		t.Fatalf("%s:%d: %v", file, lineno, err)
+	}
+	if len(input) != 0 {
+		t.Fatalf("%s:%d: out of sync: have %d strings left at EOF", file, lineno, len(input))
+	}
+	t.Logf("%d cases tested", ncase)
+}
+
+var run = []func(*Regexp, *Regexp, string) ([]int, string){
+	runFull,
+	runPartial,
+	runFullLongest,
+	runPartialLongest,
+}
+
+func runFull(re, refull *Regexp, text string) ([]int, string) {
+	refull.longest = false
+	return refull.FindStringSubmatchIndex(text), "[full]"
+}
+
+func runPartial(re, refull *Regexp, text string) ([]int, string) {
+	re.longest = false
+	return re.FindStringSubmatchIndex(text), ""
+}
+
+func runFullLongest(re, refull *Regexp, text string) ([]int, string) {
+	refull.longest = true
+	return refull.FindStringSubmatchIndex(text), "[full,longest]"
+}
+
+func runPartialLongest(re, refull *Regexp, text string) ([]int, string) {
+	re.longest = true
+	return re.FindStringSubmatchIndex(text), "[longest]"
+}
+
+var match = []func(*Regexp, *Regexp, string) (bool, string){
+	matchFull,
+	matchPartial,
+	matchFullLongest,
+	matchPartialLongest,
+}
+
+func matchFull(re, refull *Regexp, text string) (bool, string) {
+	refull.longest = false
+	return refull.MatchString(text), "[full]"
+}
+
+func matchPartial(re, refull *Regexp, text string) (bool, string) {
+	re.longest = false
+	return re.MatchString(text), ""
+}
+
+func matchFullLongest(re, refull *Regexp, text string) (bool, string) {
+	refull.longest = true
+	return refull.MatchString(text), "[full,longest]"
+}
+
+func matchPartialLongest(re, refull *Regexp, text string) (bool, string) {
+	re.longest = true
+	return re.MatchString(text), "[longest]"
+}
+
+func isSingleBytes(s string) bool {
+	for _, c := range s {
+		if c >= utf8.RuneSelf {
+			return false
+		}
+	}
+	return true
+}
+
+func tryCompile(s string) (re *Regexp, err error) {
+	// Protect against panic during Compile.
+	defer func() {
+		if r := recover(); r != nil {
+			err = fmt.Errorf("panic: %v", r)
+		}
+	}()
+	return Compile(s)
+}
+
+func parseResult(t *testing.T, file string, lineno int, res string) []int {
+	// A single - indicates no match.
+	if res == "-" {
+		return nil
+	}
+	// Otherwise, a space-separated list of pairs.
+	n := 1
+	for j := 0; j < len(res); j++ {
+		if res[j] == ' ' {
+			n++
+		}
+	}
+	out := make([]int, 2*n)
+	i := 0
+	n = 0
+	for j := 0; j <= len(res); j++ {
+		if j == len(res) || res[j] == ' ' {
+			// Process a single pair.  - means no submatch.
+			pair := res[i:j]
+			if pair == "-" {
+				out[n] = -1
+				out[n+1] = -1
+			} else {
+				loStr, hiStr, _ := strings.Cut(pair, "-")
+				lo, err1 := strconv.Atoi(loStr)
+				hi, err2 := strconv.Atoi(hiStr)
+				if err1 != nil || err2 != nil || lo > hi {
+					t.Fatalf("%s:%d: invalid pair %s", file, lineno, pair)
+				}
+				out[n] = lo
+				out[n+1] = hi
+			}
+			n += 2
+			i = j + 1
+		}
+	}
+	return out
+}
+
+func same(x, y []int) bool {
+	if len(x) != len(y) {
+		return false
+	}
+	for i, xi := range x {
+		if xi != y[i] {
+			return false
+		}
+	}
+	return true
+}
+
+// TestFowler runs this package's regexp API against the
+// POSIX regular expression tests collected by Glenn Fowler
+// at http://www2.research.att.com/~astopen/testregex/testregex.html.
+func TestFowler(t *testing.T) {
+	files, err := filepath.Glob("testdata/*.dat")
+	if err != nil {
+		t.Fatal(err)
+	}
+	for _, file := range files {
+		t.Log(file)
+		testFowler(t, file)
+	}
+}
+
+var notab = MustCompilePOSIX(`[^\t]+`)
+
+func testFowler(t *testing.T, file string) {
+	f, err := os.Open(file)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	defer f.Close()
+	b := bufio.NewReader(f)
+	lineno := 0
+	lastRegexp := ""
+Reading:
+	for {
+		lineno++
+		line, err := b.ReadString('\n')
+		if err != nil {
+			if err != io.EOF {
+				t.Errorf("%s:%d: %v", file, lineno, err)
+			}
+			break Reading
+		}
+
+		// http://www2.research.att.com/~astopen/man/man1/testregex.html
+		//
+		// INPUT FORMAT
+		//   Input lines may be blank, a comment beginning with #, or a test
+		//   specification. A specification is five fields separated by one
+		//   or more tabs. NULL denotes the empty string and NIL denotes the
+		//   0 pointer.
+		if line[0] == '#' || line[0] == '\n' {
+			continue Reading
+		}
+		line = line[:len(line)-1]
+		field := notab.FindAllString(line, -1)
+		for i, f := range field {
+			if f == "NULL" {
+				field[i] = ""
+			}
+			if f == "NIL" {
+				t.Logf("%s:%d: skip: %s", file, lineno, line)
+				continue Reading
+			}
+		}
+		if len(field) == 0 {
+			continue Reading
+		}
+
+		//   Field 1: the regex(3) flags to apply, one character per REG_feature
+		//   flag. The test is skipped if REG_feature is not supported by the
+		//   implementation. If the first character is not [BEASKLP] then the
+		//   specification is a global control line. One or more of [BEASKLP] may be
+		//   specified; the test will be repeated for each mode.
+		//
+		//     B 	basic			BRE	(grep, ed, sed)
+		//     E 	REG_EXTENDED		ERE	(egrep)
+		//     A	REG_AUGMENTED		ARE	(egrep with negation)
+		//     S	REG_SHELL		SRE	(sh glob)
+		//     K	REG_SHELL|REG_AUGMENTED	KRE	(ksh glob)
+		//     L	REG_LITERAL		LRE	(fgrep)
+		//
+		//     a	REG_LEFT|REG_RIGHT	implicit ^...$
+		//     b	REG_NOTBOL		lhs does not match ^
+		//     c	REG_COMMENT		ignore space and #...\n
+		//     d	REG_SHELL_DOT		explicit leading . match
+		//     e	REG_NOTEOL		rhs does not match $
+		//     f	REG_MULTIPLE		multiple \n separated patterns
+		//     g	FNM_LEADING_DIR		testfnmatch only -- match until /
+		//     h	REG_MULTIREF		multiple digit backref
+		//     i	REG_ICASE		ignore case
+		//     j	REG_SPAN		. matches \n
+		//     k	REG_ESCAPE		\ to escape [...] delimiter
+		//     l	REG_LEFT		implicit ^...
+		//     m	REG_MINIMAL		minimal match
+		//     n	REG_NEWLINE		explicit \n match
+		//     o	REG_ENCLOSED		(|&) magic inside [@|&](...)
+		//     p	REG_SHELL_PATH		explicit / match
+		//     q	REG_DELIMITED		delimited pattern
+		//     r	REG_RIGHT		implicit ...$
+		//     s	REG_SHELL_ESCAPED	\ not special
+		//     t	REG_MUSTDELIM		all delimiters must be specified
+		//     u	standard unspecified behavior -- errors not counted
+		//     v	REG_CLASS_ESCAPE	\ special inside [...]
+		//     w	REG_NOSUB		no subexpression match array
+		//     x	REG_LENIENT		let some errors slide
+		//     y	REG_LEFT		regexec() implicit ^...
+		//     z	REG_NULL		NULL subexpressions ok
+		//     $	                        expand C \c escapes in fields 2 and 3
+		//     /	                        field 2 is a regsubcomp() expression
+		//     =	                        field 3 is a regdecomp() expression
+		//
+		//   Field 1 control lines:
+		//
+		//     C		set LC_COLLATE and LC_CTYPE to locale in field 2
+		//
+		//     ?test ...	output field 5 if passed and != EXPECTED, silent otherwise
+		//     &test ...	output field 5 if current and previous passed
+		//     |test ...	output field 5 if current passed and previous failed
+		//     ; ...	output field 2 if previous failed
+		//     {test ...	skip if failed until }
+		//     }		end of skip
+		//
+		//     : comment		comment copied as output NOTE
+		//     :comment:test	:comment: ignored
+		//     N[OTE] comment	comment copied as output NOTE
+		//     T[EST] comment	comment
+		//
+		//     number		use number for nmatch (20 by default)
+		flag := field[0]
+		switch flag[0] {
+		case '?', '&', '|', ';', '{', '}':
+			// Ignore all the control operators.
+			// Just run everything.
+			flag = flag[1:]
+			if flag == "" {
+				continue Reading
+			}
+		case ':':
+			var ok bool
+			if _, flag, ok = strings.Cut(flag[1:], ":"); !ok {
+				t.Logf("skip: %s", line)
+				continue Reading
+			}
+		case 'C', 'N', 'T', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+			t.Logf("skip: %s", line)
+			continue Reading
+		}
+
+		// Can check field count now that we've handled the myriad comment formats.
+		if len(field) < 4 {
+			t.Errorf("%s:%d: too few fields: %s", file, lineno, line)
+			continue Reading
+		}
+
+		// Expand C escapes (a.k.a. Go escapes).
+		if strings.Contains(flag, "$") {
+			f := `"` + field[1] + `"`
+			if field[1], err = strconv.Unquote(f); err != nil {
+				t.Errorf("%s:%d: cannot unquote %s", file, lineno, f)
+			}
+			f = `"` + field[2] + `"`
+			if field[2], err = strconv.Unquote(f); err != nil {
+				t.Errorf("%s:%d: cannot unquote %s", file, lineno, f)
+			}
+		}
+
+		//   Field 2: the regular expression pattern; SAME uses the pattern from
+		//     the previous specification.
+		//
+		if field[1] == "SAME" {
+			field[1] = lastRegexp
+		}
+		lastRegexp = field[1]
+
+		//   Field 3: the string to match.
+		text := field[2]
+
+		//   Field 4: the test outcome...
+		ok, shouldCompile, shouldMatch, pos := parseFowlerResult(field[3])
+		if !ok {
+			t.Errorf("%s:%d: cannot parse result %#q", file, lineno, field[3])
+			continue Reading
+		}
+
+		//   Field 5: optional comment appended to the report.
+
+	Testing:
+		// Run test once for each specified capital letter mode that we support.
+		for _, c := range flag {
+			pattern := field[1]
+			syn := syntax.POSIX | syntax.ClassNL
+			switch c {
+			default:
+				continue Testing
+			case 'E':
+				// extended regexp (what we support)
+			case 'L':
+				// literal
+				pattern = QuoteMeta(pattern)
+			}
+
+			for _, c := range flag {
+				switch c {
+				case 'i':
+					syn |= syntax.FoldCase
+				}
+			}
+
+			re, err := compile(pattern, syn, true)
+			if err != nil {
+				if shouldCompile {
+					t.Errorf("%s:%d: %#q did not compile", file, lineno, pattern)
+				}
+				continue Testing
+			}
+			if !shouldCompile {
+				t.Errorf("%s:%d: %#q should not compile", file, lineno, pattern)
+				continue Testing
+			}
+			match := re.MatchString(text)
+			if match != shouldMatch {
+				t.Errorf("%s:%d: %#q.Match(%#q) = %v, want %v", file, lineno, pattern, text, match, shouldMatch)
+				continue Testing
+			}
+			have := re.FindStringSubmatchIndex(text)
+			if (len(have) > 0) != match {
+				t.Errorf("%s:%d: %#q.Match(%#q) = %v, but %#q.FindSubmatchIndex(%#q) = %v", file, lineno, pattern, text, match, pattern, text, have)
+				continue Testing
+			}
+			if len(have) > len(pos) {
+				have = have[:len(pos)]
+			}
+			if !same(have, pos) {
+				t.Errorf("%s:%d: %#q.FindSubmatchIndex(%#q) = %v, want %v", file, lineno, pattern, text, have, pos)
+			}
+		}
+	}
+}
+
+func parseFowlerResult(s string) (ok, compiled, matched bool, pos []int) {
+	//   Field 4: the test outcome. This is either one of the posix error
+	//     codes (with REG_ omitted) or the match array, a list of (m,n)
+	//     entries with m and n being first and last+1 positions in the
+	//     field 3 string, or NULL if REG_NOSUB is in effect and success
+	//     is expected. BADPAT is acceptable in place of any regcomp(3)
+	//     error code. The match[] array is initialized to (-2,-2) before
+	//     each test. All array elements from 0 to nmatch-1 must be specified
+	//     in the outcome. Unspecified endpoints (offset -1) are denoted by ?.
+	//     Unset endpoints (offset -2) are denoted by X. {x}(o:n) denotes a
+	//     matched (?{...}) expression, where x is the text enclosed by {...},
+	//     o is the expression ordinal counting from 1, and n is the length of
+	//     the unmatched portion of the subject string. If x starts with a
+	//     number then that is the return value of re_execf(), otherwise 0 is
+	//     returned.
+	switch {
+	case s == "":
+		// Match with no position information.
+		ok = true
+		compiled = true
+		matched = true
+		return
+	case s == "NOMATCH":
+		// Match failure.
+		ok = true
+		compiled = true
+		matched = false
+		return
+	case 'A' <= s[0] && s[0] <= 'Z':
+		// All the other error codes are compile errors.
+		ok = true
+		compiled = false
+		return
+	}
+	compiled = true
+
+	var x []int
+	for s != "" {
+		var end byte = ')'
+		if len(x)%2 == 0 {
+			if s[0] != '(' {
+				ok = false
+				return
+			}
+			s = s[1:]
+			end = ','
+		}
+		i := 0
+		for i < len(s) && s[i] != end {
+			i++
+		}
+		if i == 0 || i == len(s) {
+			ok = false
+			return
+		}
+		var v = -1
+		var err error
+		if s[:i] != "?" {
+			v, err = strconv.Atoi(s[:i])
+			if err != nil {
+				ok = false
+				return
+			}
+		}
+		x = append(x, v)
+		s = s[i+1:]
+	}
+	if len(x)%2 != 0 {
+		ok = false
+		return
+	}
+	ok = true
+	matched = true
+	pos = x
+	return
+}
+
+var text []byte
+
+func makeText(n int) []byte {
+	if len(text) >= n {
+		return text[:n]
+	}
+	text = make([]byte, n)
+	x := ^uint32(0)
+	for i := range text {
+		x += x
+		x ^= 1
+		if int32(x) < 0 {
+			x ^= 0x88888eef
+		}
+		if x%31 == 0 {
+			text[i] = '\n'
+		} else {
+			text[i] = byte(x%(0x7E+1-0x20) + 0x20)
+		}
+	}
+	return text
+}
+
+func BenchmarkMatch(b *testing.B) {
+	isRaceBuilder := strings.HasSuffix(testenv.Builder(), "-race")
+
+	for _, data := range benchData {
+		r := MustCompile(data.re)
+		for _, size := range benchSizes {
+			if (isRaceBuilder || testing.Short()) && size.n > 1<<10 {
+				continue
+			}
+			t := makeText(size.n)
+			b.Run(data.name+"/"+size.name, func(b *testing.B) {
+				b.SetBytes(int64(size.n))
+				for i := 0; i < b.N; i++ {
+					if r.Match(t) {
+						b.Fatal("match!")
+					}
+				}
+			})
+		}
+	}
+}
+
+func BenchmarkMatch_onepass_regex(b *testing.B) {
+	isRaceBuilder := strings.HasSuffix(testenv.Builder(), "-race")
+	r := MustCompile(`(?s)\A.*\z`)
+	if r.onepass == nil {
+		b.Fatalf("want onepass regex, but %q is not onepass", r)
+	}
+	for _, size := range benchSizes {
+		if (isRaceBuilder || testing.Short()) && size.n > 1<<10 {
+			continue
+		}
+		t := makeText(size.n)
+		b.Run(size.name, func(b *testing.B) {
+			b.SetBytes(int64(size.n))
+			b.ReportAllocs()
+			for i := 0; i < b.N; i++ {
+				if !r.Match(t) {
+					b.Fatal("not match!")
+				}
+			}
+		})
+	}
+}
+
+var benchData = []struct{ name, re string }{
+	{"Easy0", "ABCDEFGHIJKLMNOPQRSTUVWXYZ$"},
+	{"Easy0i", "(?i)ABCDEFGHIJklmnopqrstuvwxyz$"},
+	{"Easy1", "A[AB]B[BC]C[CD]D[DE]E[EF]F[FG]G[GH]H[HI]I[IJ]J$"},
+	{"Medium", "[XYZ]ABCDEFGHIJKLMNOPQRSTUVWXYZ$"},
+	{"Hard", "[ -~]*ABCDEFGHIJKLMNOPQRSTUVWXYZ$"},
+	{"Hard1", "ABCD|CDEF|EFGH|GHIJ|IJKL|KLMN|MNOP|OPQR|QRST|STUV|UVWX|WXYZ"},
+}
+
+var benchSizes = []struct {
+	name string
+	n    int
+}{
+	{"16", 16},
+	{"32", 32},
+	{"1K", 1 << 10},
+	{"32K", 32 << 10},
+	{"1M", 1 << 20},
+	{"32M", 32 << 20},
+}
+
+func TestLongest(t *testing.T) {
+	re, err := Compile(`a(|b)`)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if g, w := re.FindString("ab"), "a"; g != w {
+		t.Errorf("first match was %q, want %q", g, w)
+	}
+	re.Longest()
+	if g, w := re.FindString("ab"), "ab"; g != w {
+		t.Errorf("longest match was %q, want %q", g, w)
+	}
+}
+
+// TestProgramTooLongForBacktrack tests that a regex which is too long
+// for the backtracker still executes properly.
+func TestProgramTooLongForBacktrack(t *testing.T) {
+	longRegex := MustCompile(`(one|two|three|four|five|six|seven|eight|nine|ten|eleven|twelve|thirteen|fourteen|fifteen|sixteen|seventeen|eighteen|nineteen|twenty|twentyone|twentytwo|twentythree|twentyfour|twentyfive|twentysix|twentyseven|twentyeight|twentynine|thirty|thirtyone|thirtytwo|thirtythree|thirtyfour|thirtyfive|thirtysix|thirtyseven|thirtyeight|thirtynine|forty|fortyone|fortytwo|fortythree|fortyfour|fortyfive|fortysix|fortyseven|fortyeight|fortynine|fifty|fiftyone|fiftytwo|fiftythree|fiftyfour|fiftyfive|fiftysix|fiftyseven|fiftyeight|fiftynine|sixty|sixtyone|sixtytwo|sixtythree|sixtyfour|sixtyfive|sixtysix|sixtyseven|sixtyeight|sixtynine|seventy|seventyone|seventytwo|seventythree|seventyfour|seventyfive|seventysix|seventyseven|seventyeight|seventynine|eighty|eightyone|eightytwo|eightythree|eightyfour|eightyfive|eightysix|eightyseven|eightyeight|eightynine|ninety|ninetyone|ninetytwo|ninetythree|ninetyfour|ninetyfive|ninetysix|ninetyseven|ninetyeight|ninetynine|onehundred)`)
+	if !longRegex.MatchString("two") {
+		t.Errorf("longRegex.MatchString(\"two\") was false, want true")
+	}
+	if longRegex.MatchString("xxx") {
+		t.Errorf("longRegex.MatchString(\"xxx\") was true, want false")
+	}
+}
diff --git a/src/regexp/find_test.go b/src/regexp/find_test.go
new file mode 100644
index 0000000..2edbe9b
--- /dev/null
+++ b/src/regexp/find_test.go
@@ -0,0 +1,518 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package regexp
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+)
+
+// For each pattern/text pair, what is the expected output of each function?
+// We can derive the textual results from the indexed results, the non-submatch
+// results from the submatched results, the single results from the 'all' results,
+// and the byte results from the string results. Therefore the table includes
+// only the FindAllStringSubmatchIndex result.
+type FindTest struct {
+	pat     string
+	text    string
+	matches [][]int
+}
+
+func (t FindTest) String() string {
+	return fmt.Sprintf("pat: %#q text: %#q", t.pat, t.text)
+}
+
+var findTests = []FindTest{
+	{``, ``, build(1, 0, 0)},
+	{`^abcdefg`, "abcdefg", build(1, 0, 7)},
+	{`a+`, "baaab", build(1, 1, 4)},
+	{"abcd..", "abcdef", build(1, 0, 6)},
+	{`a`, "a", build(1, 0, 1)},
+	{`x`, "y", nil},
+	{`b`, "abc", build(1, 1, 2)},
+	{`.`, "a", build(1, 0, 1)},
+	{`.*`, "abcdef", build(1, 0, 6)},
+	{`^`, "abcde", build(1, 0, 0)},
+	{`$`, "abcde", build(1, 5, 5)},
+	{`^abcd$`, "abcd", build(1, 0, 4)},
+	{`^bcd'`, "abcdef", nil},
+	{`^abcd$`, "abcde", nil},
+	{`a+`, "baaab", build(1, 1, 4)},
+	{`a*`, "baaab", build(3, 0, 0, 1, 4, 5, 5)},
+	{`[a-z]+`, "abcd", build(1, 0, 4)},
+	{`[^a-z]+`, "ab1234cd", build(1, 2, 6)},
+	{`[a\-\]z]+`, "az]-bcz", build(2, 0, 4, 6, 7)},
+	{`[^\n]+`, "abcd\n", build(1, 0, 4)},
+	{`[日本語]+`, "日本語日本語", build(1, 0, 18)},
+	{`日本語+`, "日本語", build(1, 0, 9)},
+	{`日本語+`, "日本語語語語", build(1, 0, 18)},
+	{`()`, "", build(1, 0, 0, 0, 0)},
+	{`(a)`, "a", build(1, 0, 1, 0, 1)},
+	{`(.)(.)`, "日a", build(1, 0, 4, 0, 3, 3, 4)},
+	{`(.*)`, "", build(1, 0, 0, 0, 0)},
+	{`(.*)`, "abcd", build(1, 0, 4, 0, 4)},
+	{`(..)(..)`, "abcd", build(1, 0, 4, 0, 2, 2, 4)},
+	{`(([^xyz]*)(d))`, "abcd", build(1, 0, 4, 0, 4, 0, 3, 3, 4)},
+	{`((a|b|c)*(d))`, "abcd", build(1, 0, 4, 0, 4, 2, 3, 3, 4)},
+	{`(((a|b|c)*)(d))`, "abcd", build(1, 0, 4, 0, 4, 0, 3, 2, 3, 3, 4)},
+	{`\a\f\n\r\t\v`, "\a\f\n\r\t\v", build(1, 0, 6)},
+	{`[\a\f\n\r\t\v]+`, "\a\f\n\r\t\v", build(1, 0, 6)},
+
+	{`a*(|(b))c*`, "aacc", build(1, 0, 4, 2, 2, -1, -1)},
+	{`(.*).*`, "ab", build(1, 0, 2, 0, 2)},
+	{`[.]`, ".", build(1, 0, 1)},
+	{`/$`, "/abc/", build(1, 4, 5)},
+	{`/$`, "/abc", nil},
+
+	// multiple matches
+	{`.`, "abc", build(3, 0, 1, 1, 2, 2, 3)},
+	{`(.)`, "abc", build(3, 0, 1, 0, 1, 1, 2, 1, 2, 2, 3, 2, 3)},
+	{`.(.)`, "abcd", build(2, 0, 2, 1, 2, 2, 4, 3, 4)},
+	{`ab*`, "abbaab", build(3, 0, 3, 3, 4, 4, 6)},
+	{`a(b*)`, "abbaab", build(3, 0, 3, 1, 3, 3, 4, 4, 4, 4, 6, 5, 6)},
+
+	// fixed bugs
+	{`ab$`, "cab", build(1, 1, 3)},
+	{`axxb$`, "axxcb", nil},
+	{`data`, "daXY data", build(1, 5, 9)},
+	{`da(.)a$`, "daXY data", build(1, 5, 9, 7, 8)},
+	{`zx+`, "zzx", build(1, 1, 3)},
+	{`ab$`, "abcab", build(1, 3, 5)},
+	{`(aa)*$`, "a", build(1, 1, 1, -1, -1)},
+	{`(?:.|(?:.a))`, "", nil},
+	{`(?:A(?:A|a))`, "Aa", build(1, 0, 2)},
+	{`(?:A|(?:A|a))`, "a", build(1, 0, 1)},
+	{`(a){0}`, "", build(1, 0, 0, -1, -1)},
+	{`(?-s)(?:(?:^).)`, "\n", nil},
+	{`(?s)(?:(?:^).)`, "\n", build(1, 0, 1)},
+	{`(?:(?:^).)`, "\n", nil},
+	{`\b`, "x", build(2, 0, 0, 1, 1)},
+	{`\b`, "xx", build(2, 0, 0, 2, 2)},
+	{`\b`, "x y", build(4, 0, 0, 1, 1, 2, 2, 3, 3)},
+	{`\b`, "xx yy", build(4, 0, 0, 2, 2, 3, 3, 5, 5)},
+	{`\B`, "x", nil},
+	{`\B`, "xx", build(1, 1, 1)},
+	{`\B`, "x y", nil},
+	{`\B`, "xx yy", build(2, 1, 1, 4, 4)},
+	{`(|a)*`, "aa", build(3, 0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2)},
+
+	// RE2 tests
+	{`[^\S\s]`, "abcd", nil},
+	{`[^\S[:space:]]`, "abcd", nil},
+	{`[^\D\d]`, "abcd", nil},
+	{`[^\D[:digit:]]`, "abcd", nil},
+	{`(?i)\W`, "x", nil},
+	{`(?i)\W`, "k", nil},
+	{`(?i)\W`, "s", nil},
+
+	// can backslash-escape any punctuation
+	{`\!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\{\|\}\~`,
+		`!"#$%&'()*+,-./:;<=>?@[\]^_{|}~`, build(1, 0, 31)},
+	{`[\!\"\#\$\%\&\'\(\)\*\+\,\-\.\/\:\;\<\=\>\?\@\[\\\]\^\_\{\|\}\~]+`,
+		`!"#$%&'()*+,-./:;<=>?@[\]^_{|}~`, build(1, 0, 31)},
+	{"\\`", "`", build(1, 0, 1)},
+	{"[\\`]+", "`", build(1, 0, 1)},
+
+	{"\ufffd", "\xff", build(1, 0, 1)},
+	{"\ufffd", "hello\xffworld", build(1, 5, 6)},
+	{`.*`, "hello\xffworld", build(1, 0, 11)},
+	{`\x{fffd}`, "\xc2\x00", build(1, 0, 1)},
+	{"[\ufffd]", "\xff", build(1, 0, 1)},
+	{`[\x{fffd}]`, "\xc2\x00", build(1, 0, 1)},
+
+	// long set of matches (longer than startSize)
+	{
+		".",
+		"qwertyuiopasdfghjklzxcvbnm1234567890",
+		build(36, 0, 1, 1, 2, 2, 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 8, 8, 9, 9, 10,
+			10, 11, 11, 12, 12, 13, 13, 14, 14, 15, 15, 16, 16, 17, 17, 18, 18, 19, 19, 20,
+			20, 21, 21, 22, 22, 23, 23, 24, 24, 25, 25, 26, 26, 27, 27, 28, 28, 29, 29, 30,
+			30, 31, 31, 32, 32, 33, 33, 34, 34, 35, 35, 36),
+	},
+}
+
+// build is a helper to construct a [][]int by extracting n sequences from x.
+// This represents n matches with len(x)/n submatches each.
+func build(n int, x ...int) [][]int {
+	ret := make([][]int, n)
+	runLength := len(x) / n
+	j := 0
+	for i := range ret {
+		ret[i] = make([]int, runLength)
+		copy(ret[i], x[j:])
+		j += runLength
+		if j > len(x) {
+			panic("invalid build entry")
+		}
+	}
+	return ret
+}
+
+// First the simple cases.
+
+func TestFind(t *testing.T) {
+	for _, test := range findTests {
+		re := MustCompile(test.pat)
+		if re.String() != test.pat {
+			t.Errorf("String() = `%s`; should be `%s`", re.String(), test.pat)
+		}
+		result := re.Find([]byte(test.text))
+		switch {
+		case len(test.matches) == 0 && len(result) == 0:
+			// ok
+		case test.matches == nil && result != nil:
+			t.Errorf("expected no match; got one: %s", test)
+		case test.matches != nil && result == nil:
+			t.Errorf("expected match; got none: %s", test)
+		case test.matches != nil && result != nil:
+			expect := test.text[test.matches[0][0]:test.matches[0][1]]
+			if len(result) != cap(result) {
+				t.Errorf("expected capacity %d got %d: %s", len(result), cap(result), test)
+			}
+			if expect != string(result) {
+				t.Errorf("expected %q got %q: %s", expect, result, test)
+			}
+		}
+	}
+}
+
+func TestFindString(t *testing.T) {
+	for _, test := range findTests {
+		result := MustCompile(test.pat).FindString(test.text)
+		switch {
+		case len(test.matches) == 0 && len(result) == 0:
+			// ok
+		case test.matches == nil && result != "":
+			t.Errorf("expected no match; got one: %s", test)
+		case test.matches != nil && result == "":
+			// Tricky because an empty result has two meanings: no match or empty match.
+			if test.matches[0][0] != test.matches[0][1] {
+				t.Errorf("expected match; got none: %s", test)
+			}
+		case test.matches != nil && result != "":
+			expect := test.text[test.matches[0][0]:test.matches[0][1]]
+			if expect != result {
+				t.Errorf("expected %q got %q: %s", expect, result, test)
+			}
+		}
+	}
+}
+
+func testFindIndex(test *FindTest, result []int, t *testing.T) {
+	switch {
+	case len(test.matches) == 0 && len(result) == 0:
+		// ok
+	case test.matches == nil && result != nil:
+		t.Errorf("expected no match; got one: %s", test)
+	case test.matches != nil && result == nil:
+		t.Errorf("expected match; got none: %s", test)
+	case test.matches != nil && result != nil:
+		expect := test.matches[0]
+		if expect[0] != result[0] || expect[1] != result[1] {
+			t.Errorf("expected %v got %v: %s", expect, result, test)
+		}
+	}
+}
+
+func TestFindIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindIndex(&test, MustCompile(test.pat).FindIndex([]byte(test.text)), t)
+	}
+}
+
+func TestFindStringIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindIndex(&test, MustCompile(test.pat).FindStringIndex(test.text), t)
+	}
+}
+
+func TestFindReaderIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindIndex(&test, MustCompile(test.pat).FindReaderIndex(strings.NewReader(test.text)), t)
+	}
+}
+
+// Now come the simple All cases.
+
+func TestFindAll(t *testing.T) {
+	for _, test := range findTests {
+		result := MustCompile(test.pat).FindAll([]byte(test.text), -1)
+		switch {
+		case test.matches == nil && result == nil:
+			// ok
+		case test.matches == nil && result != nil:
+			t.Errorf("expected no match; got one: %s", test)
+		case test.matches != nil && result == nil:
+			t.Fatalf("expected match; got none: %s", test)
+		case test.matches != nil && result != nil:
+			if len(test.matches) != len(result) {
+				t.Errorf("expected %d matches; got %d: %s", len(test.matches), len(result), test)
+				continue
+			}
+			for k, e := range test.matches {
+				got := result[k]
+				if len(got) != cap(got) {
+					t.Errorf("match %d: expected capacity %d got %d: %s", k, len(got), cap(got), test)
+				}
+				expect := test.text[e[0]:e[1]]
+				if expect != string(got) {
+					t.Errorf("match %d: expected %q got %q: %s", k, expect, got, test)
+				}
+			}
+		}
+	}
+}
+
+func TestFindAllString(t *testing.T) {
+	for _, test := range findTests {
+		result := MustCompile(test.pat).FindAllString(test.text, -1)
+		switch {
+		case test.matches == nil && result == nil:
+			// ok
+		case test.matches == nil && result != nil:
+			t.Errorf("expected no match; got one: %s", test)
+		case test.matches != nil && result == nil:
+			t.Errorf("expected match; got none: %s", test)
+		case test.matches != nil && result != nil:
+			if len(test.matches) != len(result) {
+				t.Errorf("expected %d matches; got %d: %s", len(test.matches), len(result), test)
+				continue
+			}
+			for k, e := range test.matches {
+				expect := test.text[e[0]:e[1]]
+				if expect != result[k] {
+					t.Errorf("expected %q got %q: %s", expect, result, test)
+				}
+			}
+		}
+	}
+}
+
+func testFindAllIndex(test *FindTest, result [][]int, t *testing.T) {
+	switch {
+	case test.matches == nil && result == nil:
+		// ok
+	case test.matches == nil && result != nil:
+		t.Errorf("expected no match; got one: %s", test)
+	case test.matches != nil && result == nil:
+		t.Errorf("expected match; got none: %s", test)
+	case test.matches != nil && result != nil:
+		if len(test.matches) != len(result) {
+			t.Errorf("expected %d matches; got %d: %s", len(test.matches), len(result), test)
+			return
+		}
+		for k, e := range test.matches {
+			if e[0] != result[k][0] || e[1] != result[k][1] {
+				t.Errorf("match %d: expected %v got %v: %s", k, e, result[k], test)
+			}
+		}
+	}
+}
+
+func TestFindAllIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindAllIndex(&test, MustCompile(test.pat).FindAllIndex([]byte(test.text), -1), t)
+	}
+}
+
+func TestFindAllStringIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindAllIndex(&test, MustCompile(test.pat).FindAllStringIndex(test.text, -1), t)
+	}
+}
+
+// Now come the Submatch cases.
+
+func testSubmatchBytes(test *FindTest, n int, submatches []int, result [][]byte, t *testing.T) {
+	if len(submatches) != len(result)*2 {
+		t.Errorf("match %d: expected %d submatches; got %d: %s", n, len(submatches)/2, len(result), test)
+		return
+	}
+	for k := 0; k < len(submatches); k += 2 {
+		if submatches[k] == -1 {
+			if result[k/2] != nil {
+				t.Errorf("match %d: expected nil got %q: %s", n, result, test)
+			}
+			continue
+		}
+		got := result[k/2]
+		if len(got) != cap(got) {
+			t.Errorf("match %d: expected capacity %d got %d: %s", n, len(got), cap(got), test)
+			return
+		}
+		expect := test.text[submatches[k]:submatches[k+1]]
+		if expect != string(got) {
+			t.Errorf("match %d: expected %q got %q: %s", n, expect, got, test)
+			return
+		}
+	}
+}
+
+func TestFindSubmatch(t *testing.T) {
+	for _, test := range findTests {
+		result := MustCompile(test.pat).FindSubmatch([]byte(test.text))
+		switch {
+		case test.matches == nil && result == nil:
+			// ok
+		case test.matches == nil && result != nil:
+			t.Errorf("expected no match; got one: %s", test)
+		case test.matches != nil && result == nil:
+			t.Errorf("expected match; got none: %s", test)
+		case test.matches != nil && result != nil:
+			testSubmatchBytes(&test, 0, test.matches[0], result, t)
+		}
+	}
+}
+
+func testSubmatchString(test *FindTest, n int, submatches []int, result []string, t *testing.T) {
+	if len(submatches) != len(result)*2 {
+		t.Errorf("match %d: expected %d submatches; got %d: %s", n, len(submatches)/2, len(result), test)
+		return
+	}
+	for k := 0; k < len(submatches); k += 2 {
+		if submatches[k] == -1 {
+			if result[k/2] != "" {
+				t.Errorf("match %d: expected nil got %q: %s", n, result, test)
+			}
+			continue
+		}
+		expect := test.text[submatches[k]:submatches[k+1]]
+		if expect != result[k/2] {
+			t.Errorf("match %d: expected %q got %q: %s", n, expect, result, test)
+			return
+		}
+	}
+}
+
+func TestFindStringSubmatch(t *testing.T) {
+	for _, test := range findTests {
+		result := MustCompile(test.pat).FindStringSubmatch(test.text)
+		switch {
+		case test.matches == nil && result == nil:
+			// ok
+		case test.matches == nil && result != nil:
+			t.Errorf("expected no match; got one: %s", test)
+		case test.matches != nil && result == nil:
+			t.Errorf("expected match; got none: %s", test)
+		case test.matches != nil && result != nil:
+			testSubmatchString(&test, 0, test.matches[0], result, t)
+		}
+	}
+}
+
+func testSubmatchIndices(test *FindTest, n int, expect, result []int, t *testing.T) {
+	if len(expect) != len(result) {
+		t.Errorf("match %d: expected %d matches; got %d: %s", n, len(expect)/2, len(result)/2, test)
+		return
+	}
+	for k, e := range expect {
+		if e != result[k] {
+			t.Errorf("match %d: submatch error: expected %v got %v: %s", n, expect, result, test)
+		}
+	}
+}
+
+func testFindSubmatchIndex(test *FindTest, result []int, t *testing.T) {
+	switch {
+	case test.matches == nil && result == nil:
+		// ok
+	case test.matches == nil && result != nil:
+		t.Errorf("expected no match; got one: %s", test)
+	case test.matches != nil && result == nil:
+		t.Errorf("expected match; got none: %s", test)
+	case test.matches != nil && result != nil:
+		testSubmatchIndices(test, 0, test.matches[0], result, t)
+	}
+}
+
+func TestFindSubmatchIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindSubmatchIndex(&test, MustCompile(test.pat).FindSubmatchIndex([]byte(test.text)), t)
+	}
+}
+
+func TestFindStringSubmatchIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindSubmatchIndex(&test, MustCompile(test.pat).FindStringSubmatchIndex(test.text), t)
+	}
+}
+
+func TestFindReaderSubmatchIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindSubmatchIndex(&test, MustCompile(test.pat).FindReaderSubmatchIndex(strings.NewReader(test.text)), t)
+	}
+}
+
+// Now come the monster AllSubmatch cases.
+
+func TestFindAllSubmatch(t *testing.T) {
+	for _, test := range findTests {
+		result := MustCompile(test.pat).FindAllSubmatch([]byte(test.text), -1)
+		switch {
+		case test.matches == nil && result == nil:
+			// ok
+		case test.matches == nil && result != nil:
+			t.Errorf("expected no match; got one: %s", test)
+		case test.matches != nil && result == nil:
+			t.Errorf("expected match; got none: %s", test)
+		case len(test.matches) != len(result):
+			t.Errorf("expected %d matches; got %d: %s", len(test.matches), len(result), test)
+		case test.matches != nil && result != nil:
+			for k, match := range test.matches {
+				testSubmatchBytes(&test, k, match, result[k], t)
+			}
+		}
+	}
+}
+
+func TestFindAllStringSubmatch(t *testing.T) {
+	for _, test := range findTests {
+		result := MustCompile(test.pat).FindAllStringSubmatch(test.text, -1)
+		switch {
+		case test.matches == nil && result == nil:
+			// ok
+		case test.matches == nil && result != nil:
+			t.Errorf("expected no match; got one: %s", test)
+		case test.matches != nil && result == nil:
+			t.Errorf("expected match; got none: %s", test)
+		case len(test.matches) != len(result):
+			t.Errorf("expected %d matches; got %d: %s", len(test.matches), len(result), test)
+		case test.matches != nil && result != nil:
+			for k, match := range test.matches {
+				testSubmatchString(&test, k, match, result[k], t)
+			}
+		}
+	}
+}
+
+func testFindAllSubmatchIndex(test *FindTest, result [][]int, t *testing.T) {
+	switch {
+	case test.matches == nil && result == nil:
+		// ok
+	case test.matches == nil && result != nil:
+		t.Errorf("expected no match; got one: %s", test)
+	case test.matches != nil && result == nil:
+		t.Errorf("expected match; got none: %s", test)
+	case len(test.matches) != len(result):
+		t.Errorf("expected %d matches; got %d: %s", len(test.matches), len(result), test)
+	case test.matches != nil && result != nil:
+		for k, match := range test.matches {
+			testSubmatchIndices(test, k, match, result[k], t)
+		}
+	}
+}
+
+func TestFindAllSubmatchIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindAllSubmatchIndex(&test, MustCompile(test.pat).FindAllSubmatchIndex([]byte(test.text), -1), t)
+	}
+}
+
+func TestFindAllStringSubmatchIndex(t *testing.T) {
+	for _, test := range findTests {
+		testFindAllSubmatchIndex(&test, MustCompile(test.pat).FindAllStringSubmatchIndex(test.text, -1), t)
+	}
+}
diff --git a/src/regexp/onepass.go b/src/regexp/onepass.go
new file mode 100644
index 0000000..b3066e8
--- /dev/null
+++ b/src/regexp/onepass.go
@@ -0,0 +1,507 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package regexp
+
+import (
+	"regexp/syntax"
+	"sort"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// "One-pass" regexp execution.
+// Some regexps can be analyzed to determine that they never need
+// backtracking: they are guaranteed to run in one pass over the string
+// without bothering to save all the usual NFA state.
+// Detect those and execute them more quickly.
+
+// A onePassProg is a compiled one-pass regular expression program.
+// It is the same as syntax.Prog except for the use of onePassInst.
+type onePassProg struct {
+	Inst   []onePassInst
+	Start  int // index of start instruction
+	NumCap int // number of InstCapture insts in re
+}
+
+// A onePassInst is a single instruction in a one-pass regular expression program.
+// It is the same as syntax.Inst except for the new 'Next' field.
+type onePassInst struct {
+	syntax.Inst
+	Next []uint32
+}
+
+// onePassPrefix returns a literal string that all matches for the
+// regexp must start with. Complete is true if the prefix
+// is the entire match. Pc is the index of the last rune instruction
+// in the string. The onePassPrefix skips over the mandatory
+// EmptyBeginText.
+func onePassPrefix(p *syntax.Prog) (prefix string, complete bool, pc uint32) {
+	i := &p.Inst[p.Start]
+	if i.Op != syntax.InstEmptyWidth || (syntax.EmptyOp(i.Arg))&syntax.EmptyBeginText == 0 {
+		return "", i.Op == syntax.InstMatch, uint32(p.Start)
+	}
+	pc = i.Out
+	i = &p.Inst[pc]
+	for i.Op == syntax.InstNop {
+		pc = i.Out
+		i = &p.Inst[pc]
+	}
+	// Avoid allocation of buffer if prefix is empty.
+	if iop(i) != syntax.InstRune || len(i.Rune) != 1 {
+		return "", i.Op == syntax.InstMatch, uint32(p.Start)
+	}
+
+	// Have prefix; gather characters.
+	var buf strings.Builder
+	for iop(i) == syntax.InstRune && len(i.Rune) == 1 && syntax.Flags(i.Arg)&syntax.FoldCase == 0 && i.Rune[0] != utf8.RuneError {
+		buf.WriteRune(i.Rune[0])
+		pc, i = i.Out, &p.Inst[i.Out]
+	}
+	if i.Op == syntax.InstEmptyWidth &&
+		syntax.EmptyOp(i.Arg)&syntax.EmptyEndText != 0 &&
+		p.Inst[i.Out].Op == syntax.InstMatch {
+		complete = true
+	}
+	return buf.String(), complete, pc
+}
+
+// onePassNext selects the next actionable state of the prog, based on the input character.
+// It should only be called when i.Op == InstAlt or InstAltMatch, and from the one-pass machine.
+// One of the alternates may ultimately lead without input to end of line. If the instruction
+// is InstAltMatch the path to the InstMatch is in i.Out, the normal node in i.Next.
+func onePassNext(i *onePassInst, r rune) uint32 {
+	next := i.MatchRunePos(r)
+	if next >= 0 {
+		return i.Next[next]
+	}
+	if i.Op == syntax.InstAltMatch {
+		return i.Out
+	}
+	return 0
+}
+
+func iop(i *syntax.Inst) syntax.InstOp {
+	op := i.Op
+	switch op {
+	case syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
+		op = syntax.InstRune
+	}
+	return op
+}
+
+// Sparse Array implementation is used as a queueOnePass.
+type queueOnePass struct {
+	sparse          []uint32
+	dense           []uint32
+	size, nextIndex uint32
+}
+
+func (q *queueOnePass) empty() bool {
+	return q.nextIndex >= q.size
+}
+
+func (q *queueOnePass) next() (n uint32) {
+	n = q.dense[q.nextIndex]
+	q.nextIndex++
+	return
+}
+
+func (q *queueOnePass) clear() {
+	q.size = 0
+	q.nextIndex = 0
+}
+
+func (q *queueOnePass) contains(u uint32) bool {
+	if u >= uint32(len(q.sparse)) {
+		return false
+	}
+	return q.sparse[u] < q.size && q.dense[q.sparse[u]] == u
+}
+
+func (q *queueOnePass) insert(u uint32) {
+	if !q.contains(u) {
+		q.insertNew(u)
+	}
+}
+
+func (q *queueOnePass) insertNew(u uint32) {
+	if u >= uint32(len(q.sparse)) {
+		return
+	}
+	q.sparse[u] = q.size
+	q.dense[q.size] = u
+	q.size++
+}
+
+func newQueue(size int) (q *queueOnePass) {
+	return &queueOnePass{
+		sparse: make([]uint32, size),
+		dense:  make([]uint32, size),
+	}
+}
+
+// mergeRuneSets merges two non-intersecting runesets, and returns the merged result,
+// and a NextIp array. The idea is that if a rune matches the OnePassRunes at index
+// i, NextIp[i/2] is the target. If the input sets intersect, an empty runeset and a
+// NextIp array with the single element mergeFailed is returned.
+// The code assumes that both inputs contain ordered and non-intersecting rune pairs.
+const mergeFailed = uint32(0xffffffff)
+
+var (
+	noRune = []rune{}
+	noNext = []uint32{mergeFailed}
+)
+
+func mergeRuneSets(leftRunes, rightRunes *[]rune, leftPC, rightPC uint32) ([]rune, []uint32) {
+	leftLen := len(*leftRunes)
+	rightLen := len(*rightRunes)
+	if leftLen&0x1 != 0 || rightLen&0x1 != 0 {
+		panic("mergeRuneSets odd length []rune")
+	}
+	var (
+		lx, rx int
+	)
+	merged := make([]rune, 0)
+	next := make([]uint32, 0)
+	ok := true
+	defer func() {
+		if !ok {
+			merged = nil
+			next = nil
+		}
+	}()
+
+	ix := -1
+	extend := func(newLow *int, newArray *[]rune, pc uint32) bool {
+		if ix > 0 && (*newArray)[*newLow] <= merged[ix] {
+			return false
+		}
+		merged = append(merged, (*newArray)[*newLow], (*newArray)[*newLow+1])
+		*newLow += 2
+		ix += 2
+		next = append(next, pc)
+		return true
+	}
+
+	for lx < leftLen || rx < rightLen {
+		switch {
+		case rx >= rightLen:
+			ok = extend(&lx, leftRunes, leftPC)
+		case lx >= leftLen:
+			ok = extend(&rx, rightRunes, rightPC)
+		case (*rightRunes)[rx] < (*leftRunes)[lx]:
+			ok = extend(&rx, rightRunes, rightPC)
+		default:
+			ok = extend(&lx, leftRunes, leftPC)
+		}
+		if !ok {
+			return noRune, noNext
+		}
+	}
+	return merged, next
+}
+
+// cleanupOnePass drops working memory, and restores certain shortcut instructions.
+func cleanupOnePass(prog *onePassProg, original *syntax.Prog) {
+	for ix, instOriginal := range original.Inst {
+		switch instOriginal.Op {
+		case syntax.InstAlt, syntax.InstAltMatch, syntax.InstRune:
+		case syntax.InstCapture, syntax.InstEmptyWidth, syntax.InstNop, syntax.InstMatch, syntax.InstFail:
+			prog.Inst[ix].Next = nil
+		case syntax.InstRune1, syntax.InstRuneAny, syntax.InstRuneAnyNotNL:
+			prog.Inst[ix].Next = nil
+			prog.Inst[ix] = onePassInst{Inst: instOriginal}
+		}
+	}
+}
+
+// onePassCopy creates a copy of the original Prog, as we'll be modifying it.
+func onePassCopy(prog *syntax.Prog) *onePassProg {
+	p := &onePassProg{
+		Start:  prog.Start,
+		NumCap: prog.NumCap,
+		Inst:   make([]onePassInst, len(prog.Inst)),
+	}
+	for i, inst := range prog.Inst {
+		p.Inst[i] = onePassInst{Inst: inst}
+	}
+
+	// rewrites one or more common Prog constructs that enable some otherwise
+	// non-onepass Progs to be onepass. A:BD (for example) means an InstAlt at
+	// ip A, that points to ips B & C.
+	// A:BC + B:DA => A:BC + B:CD
+	// A:BC + B:DC => A:DC + B:DC
+	for pc := range p.Inst {
+		switch p.Inst[pc].Op {
+		default:
+			continue
+		case syntax.InstAlt, syntax.InstAltMatch:
+			// A:Bx + B:Ay
+			p_A_Other := &p.Inst[pc].Out
+			p_A_Alt := &p.Inst[pc].Arg
+			// make sure a target is another Alt
+			instAlt := p.Inst[*p_A_Alt]
+			if !(instAlt.Op == syntax.InstAlt || instAlt.Op == syntax.InstAltMatch) {
+				p_A_Alt, p_A_Other = p_A_Other, p_A_Alt
+				instAlt = p.Inst[*p_A_Alt]
+				if !(instAlt.Op == syntax.InstAlt || instAlt.Op == syntax.InstAltMatch) {
+					continue
+				}
+			}
+			instOther := p.Inst[*p_A_Other]
+			// Analyzing both legs pointing to Alts is for another day
+			if instOther.Op == syntax.InstAlt || instOther.Op == syntax.InstAltMatch {
+				// too complicated
+				continue
+			}
+			// simple empty transition loop
+			// A:BC + B:DA => A:BC + B:DC
+			p_B_Alt := &p.Inst[*p_A_Alt].Out
+			p_B_Other := &p.Inst[*p_A_Alt].Arg
+			patch := false
+			if instAlt.Out == uint32(pc) {
+				patch = true
+			} else if instAlt.Arg == uint32(pc) {
+				patch = true
+				p_B_Alt, p_B_Other = p_B_Other, p_B_Alt
+			}
+			if patch {
+				*p_B_Alt = *p_A_Other
+			}
+
+			// empty transition to common target
+			// A:BC + B:DC => A:DC + B:DC
+			if *p_A_Other == *p_B_Alt {
+				*p_A_Alt = *p_B_Other
+			}
+		}
+	}
+	return p
+}
+
+// runeSlice exists to permit sorting the case-folded rune sets.
+type runeSlice []rune
+
+func (p runeSlice) Len() int           { return len(p) }
+func (p runeSlice) Less(i, j int) bool { return p[i] < p[j] }
+func (p runeSlice) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+
+var anyRuneNotNL = []rune{0, '\n' - 1, '\n' + 1, unicode.MaxRune}
+var anyRune = []rune{0, unicode.MaxRune}
+
+// makeOnePass creates a onepass Prog, if possible. It is possible if at any alt,
+// the match engine can always tell which branch to take. The routine may modify
+// p if it is turned into a onepass Prog. If it isn't possible for this to be a
+// onepass Prog, the Prog nil is returned. makeOnePass is recursive
+// to the size of the Prog.
+func makeOnePass(p *onePassProg) *onePassProg {
+	// If the machine is very long, it's not worth the time to check if we can use one pass.
+	if len(p.Inst) >= 1000 {
+		return nil
+	}
+
+	var (
+		instQueue    = newQueue(len(p.Inst))
+		visitQueue   = newQueue(len(p.Inst))
+		check        func(uint32, []bool) bool
+		onePassRunes = make([][]rune, len(p.Inst))
+	)
+
+	// check that paths from Alt instructions are unambiguous, and rebuild the new
+	// program as a onepass program
+	check = func(pc uint32, m []bool) (ok bool) {
+		ok = true
+		inst := &p.Inst[pc]
+		if visitQueue.contains(pc) {
+			return
+		}
+		visitQueue.insert(pc)
+		switch inst.Op {
+		case syntax.InstAlt, syntax.InstAltMatch:
+			ok = check(inst.Out, m) && check(inst.Arg, m)
+			// check no-input paths to InstMatch
+			matchOut := m[inst.Out]
+			matchArg := m[inst.Arg]
+			if matchOut && matchArg {
+				ok = false
+				break
+			}
+			// Match on empty goes in inst.Out
+			if matchArg {
+				inst.Out, inst.Arg = inst.Arg, inst.Out
+				matchOut, matchArg = matchArg, matchOut
+			}
+			if matchOut {
+				m[pc] = true
+				inst.Op = syntax.InstAltMatch
+			}
+
+			// build a dispatch operator from the two legs of the alt.
+			onePassRunes[pc], inst.Next = mergeRuneSets(
+				&onePassRunes[inst.Out], &onePassRunes[inst.Arg], inst.Out, inst.Arg)
+			if len(inst.Next) > 0 && inst.Next[0] == mergeFailed {
+				ok = false
+				break
+			}
+		case syntax.InstCapture, syntax.InstNop:
+			ok = check(inst.Out, m)
+			m[pc] = m[inst.Out]
+			// pass matching runes back through these no-ops.
+			onePassRunes[pc] = append([]rune{}, onePassRunes[inst.Out]...)
+			inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+			for i := range inst.Next {
+				inst.Next[i] = inst.Out
+			}
+		case syntax.InstEmptyWidth:
+			ok = check(inst.Out, m)
+			m[pc] = m[inst.Out]
+			onePassRunes[pc] = append([]rune{}, onePassRunes[inst.Out]...)
+			inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+			for i := range inst.Next {
+				inst.Next[i] = inst.Out
+			}
+		case syntax.InstMatch, syntax.InstFail:
+			m[pc] = inst.Op == syntax.InstMatch
+		case syntax.InstRune:
+			m[pc] = false
+			if len(inst.Next) > 0 {
+				break
+			}
+			instQueue.insert(inst.Out)
+			if len(inst.Rune) == 0 {
+				onePassRunes[pc] = []rune{}
+				inst.Next = []uint32{inst.Out}
+				break
+			}
+			runes := make([]rune, 0)
+			if len(inst.Rune) == 1 && 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)
+				}
+				sort.Sort(runeSlice(runes))
+			} else {
+				runes = append(runes, inst.Rune...)
+			}
+			onePassRunes[pc] = runes
+			inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+			for i := range inst.Next {
+				inst.Next[i] = inst.Out
+			}
+			inst.Op = syntax.InstRune
+		case syntax.InstRune1:
+			m[pc] = false
+			if len(inst.Next) > 0 {
+				break
+			}
+			instQueue.insert(inst.Out)
+			runes := []rune{}
+			// expand case-folded runes
+			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)
+				}
+				sort.Sort(runeSlice(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 {
+				inst.Next[i] = inst.Out
+			}
+			inst.Op = syntax.InstRune
+		case syntax.InstRuneAny:
+			m[pc] = false
+			if len(inst.Next) > 0 {
+				break
+			}
+			instQueue.insert(inst.Out)
+			onePassRunes[pc] = append([]rune{}, anyRune...)
+			inst.Next = []uint32{inst.Out}
+		case syntax.InstRuneAnyNotNL:
+			m[pc] = false
+			if len(inst.Next) > 0 {
+				break
+			}
+			instQueue.insert(inst.Out)
+			onePassRunes[pc] = append([]rune{}, anyRuneNotNL...)
+			inst.Next = make([]uint32, len(onePassRunes[pc])/2+1)
+			for i := range inst.Next {
+				inst.Next[i] = inst.Out
+			}
+		}
+		return
+	}
+
+	instQueue.clear()
+	instQueue.insert(uint32(p.Start))
+	m := make([]bool, len(p.Inst))
+	for !instQueue.empty() {
+		visitQueue.clear()
+		pc := instQueue.next()
+		if !check(pc, m) {
+			p = nil
+			break
+		}
+	}
+	if p != nil {
+		for i := range p.Inst {
+			p.Inst[i].Rune = onePassRunes[i]
+		}
+	}
+	return p
+}
+
+// compileOnePass returns a new *syntax.Prog suitable for onePass execution if the original Prog
+// can be recharacterized as a one-pass regexp program, or syntax.nil if the
+// Prog cannot be converted. For a one pass prog, the fundamental condition that must
+// be true is: at any InstAlt, there must be no ambiguity about what branch to  take.
+func compileOnePass(prog *syntax.Prog) (p *onePassProg) {
+	if prog.Start == 0 {
+		return nil
+	}
+	// onepass regexp is anchored
+	if prog.Inst[prog.Start].Op != syntax.InstEmptyWidth ||
+		syntax.EmptyOp(prog.Inst[prog.Start].Arg)&syntax.EmptyBeginText != syntax.EmptyBeginText {
+		return nil
+	}
+	// every instruction leading to InstMatch must be EmptyEndText
+	for _, inst := range prog.Inst {
+		opOut := prog.Inst[inst.Out].Op
+		switch inst.Op {
+		default:
+			if opOut == syntax.InstMatch {
+				return nil
+			}
+		case syntax.InstAlt, syntax.InstAltMatch:
+			if opOut == syntax.InstMatch || prog.Inst[inst.Arg].Op == syntax.InstMatch {
+				return nil
+			}
+		case syntax.InstEmptyWidth:
+			if opOut == syntax.InstMatch {
+				if syntax.EmptyOp(inst.Arg)&syntax.EmptyEndText == syntax.EmptyEndText {
+					continue
+				}
+				return nil
+			}
+		}
+	}
+	// Creates a slightly optimized copy of the original Prog
+	// that cleans up some Prog idioms that block valid onepass programs
+	p = onePassCopy(prog)
+
+	// checkAmbiguity on InstAlts, build onepass Prog if possible
+	p = makeOnePass(p)
+
+	if p != nil {
+		cleanupOnePass(p, prog)
+	}
+	return p
+}
diff --git a/src/regexp/onepass_test.go b/src/regexp/onepass_test.go
new file mode 100644
index 0000000..6a42eda
--- /dev/null
+++ b/src/regexp/onepass_test.go
@@ -0,0 +1,225 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package regexp
+
+import (
+	"reflect"
+	"regexp/syntax"
+	"strings"
+	"testing"
+)
+
+var runeMergeTests = []struct {
+	left, right, merged []rune
+	next                []uint32
+	leftPC, rightPC     uint32
+}{
+	{
+		// empty rhs
+		[]rune{69, 69},
+		[]rune{},
+		[]rune{69, 69},
+		[]uint32{1},
+		1, 2,
+	},
+	{
+		// identical runes, identical targets
+		[]rune{69, 69},
+		[]rune{69, 69},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 1,
+	},
+	{
+		// identical runes, different targets
+		[]rune{69, 69},
+		[]rune{69, 69},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 2,
+	},
+	{
+		// append right-first
+		[]rune{69, 69},
+		[]rune{71, 71},
+		[]rune{69, 69, 71, 71},
+		[]uint32{1, 2},
+		1, 2,
+	},
+	{
+		// append, left-first
+		[]rune{71, 71},
+		[]rune{69, 69},
+		[]rune{69, 69, 71, 71},
+		[]uint32{2, 1},
+		1, 2,
+	},
+	{
+		// successful interleave
+		[]rune{60, 60, 71, 71, 101, 101},
+		[]rune{69, 69, 88, 88},
+		[]rune{60, 60, 69, 69, 71, 71, 88, 88, 101, 101},
+		[]uint32{1, 2, 1, 2, 1},
+		1, 2,
+	},
+	{
+		// left surrounds right
+		[]rune{69, 74},
+		[]rune{71, 71},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 2,
+	},
+	{
+		// right surrounds left
+		[]rune{69, 74},
+		[]rune{68, 75},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 2,
+	},
+	{
+		// overlap at interval begin
+		[]rune{69, 74},
+		[]rune{74, 75},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 2,
+	},
+	{
+		// overlap ar interval end
+		[]rune{69, 74},
+		[]rune{65, 69},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 2,
+	},
+	{
+		// overlap from above
+		[]rune{69, 74},
+		[]rune{71, 74},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 2,
+	},
+	{
+		// overlap from below
+		[]rune{69, 74},
+		[]rune{65, 71},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 2,
+	},
+	{
+		// out of order []rune
+		[]rune{69, 74, 60, 65},
+		[]rune{66, 67},
+		[]rune{},
+		[]uint32{mergeFailed},
+		1, 2,
+	},
+}
+
+func TestMergeRuneSet(t *testing.T) {
+	for ix, test := range runeMergeTests {
+		merged, next := mergeRuneSets(&test.left, &test.right, test.leftPC, test.rightPC)
+		if !reflect.DeepEqual(merged, test.merged) {
+			t.Errorf("mergeRuneSet :%d (%v, %v) merged\n have\n%v\nwant\n%v", ix, test.left, test.right, merged, test.merged)
+		}
+		if !reflect.DeepEqual(next, test.next) {
+			t.Errorf("mergeRuneSet :%d(%v, %v) next\n have\n%v\nwant\n%v", ix, test.left, test.right, next, test.next)
+		}
+	}
+}
+
+var onePassTests = []struct {
+	re        string
+	isOnePass bool
+}{
+	{`^(?:a|(?:a*))$`, false},
+	{`^(?:(a)|(?:a*))$`, false},
+	{`^(?:(?:(?:.(?:$))?))$`, true},
+	{`^abcd$`, true},
+	{`^(?:(?:a{0,})*?)$`, false},
+	{`^(?:(?:a+)*)$`, true},
+	{`^(?:(?:a|(?:aa)))$`, true},
+	{`^(?:[^\s\S])$`, true},
+	{`^(?:(?:a{3,4}){0,})$`, false},
+	{`^(?:(?:(?:a*)+))$`, true},
+	{`^[a-c]+$`, true},
+	{`^[a-c]*$`, true},
+	{`^(?:a*)$`, true},
+	{`^(?:(?:aa)|a)$`, true},
+	{`^[a-c]*`, false},
+	{`^...$`, true},
+	{`^(?:a|(?:aa))$`, true},
+	{`^a((b))c$`, true},
+	{`^a.[l-nA-Cg-j]?e$`, true},
+	{`^a((b))$`, true},
+	{`^a(?:(b)|(c))c$`, true},
+	{`^a(?:(b*)|(c))c$`, false},
+	{`^a(?:b|c)$`, true},
+	{`^a(?:b?|c)$`, true},
+	{`^a(?:b?|c?)$`, false},
+	{`^a(?:b?|c+)$`, true},
+	{`^a(?:b+|(bc))d$`, false},
+	{`^a(?:bc)+$`, true},
+	{`^a(?:[bcd])+$`, true},
+	{`^a((?:[bcd])+)$`, true},
+	{`^a(:?b|c)*d$`, true},
+	{`^.bc(d|e)*$`, true},
+	{`^(?:(?:aa)|.)$`, false},
+	{`^(?:(?:a{1,2}){1,2})$`, false},
+	{`^l` + strings.Repeat("o", 2<<8) + `ng$`, true},
+}
+
+func TestCompileOnePass(t *testing.T) {
+	var (
+		p   *syntax.Prog
+		re  *syntax.Regexp
+		err error
+	)
+	for _, test := range onePassTests {
+		if re, err = syntax.Parse(test.re, syntax.Perl); err != nil {
+			t.Errorf("Parse(%q) got err:%s, want success", test.re, err)
+			continue
+		}
+		// needs to be done before compile...
+		re = re.Simplify()
+		if p, err = syntax.Compile(re); err != nil {
+			t.Errorf("Compile(%q) got err:%s, want success", test.re, err)
+			continue
+		}
+		isOnePass := compileOnePass(p) != nil
+		if isOnePass != test.isOnePass {
+			t.Errorf("CompileOnePass(%q) got isOnePass=%v, expected %v", test.re, isOnePass, test.isOnePass)
+		}
+	}
+}
+
+// TODO(cespare): Unify with onePassTests and rationalize one-pass test cases.
+var onePassTests1 = []struct {
+	re    string
+	match string
+}{
+	{`^a(/b+(#c+)*)*$`, "a/b#c"}, // golang.org/issue/11905
+}
+
+func TestRunOnePass(t *testing.T) {
+	for _, test := range onePassTests1 {
+		re, err := Compile(test.re)
+		if err != nil {
+			t.Errorf("Compile(%q): got err: %s", test.re, err)
+			continue
+		}
+		if re.onepass == nil {
+			t.Errorf("Compile(%q): got nil, want one-pass", test.re)
+			continue
+		}
+		if !re.MatchString(test.match) {
+			t.Errorf("onepass %q did not match %q", test.re, test.match)
+		}
+	}
+}
diff --git a/src/regexp/regexp.go b/src/regexp/regexp.go
new file mode 100644
index 0000000..462f235
--- /dev/null
+++ b/src/regexp/regexp.go
@@ -0,0 +1,1304 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package regexp implements regular expression search.
+//
+// The syntax of the regular expressions accepted is the same
+// general syntax used by Perl, Python, and other languages.
+// More precisely, it is the syntax accepted by RE2 and described at
+// https://golang.org/s/re2syntax, except for \C.
+// For an overview of the syntax, see the [regexp/syntax] package.
+//
+// The regexp implementation provided by this package is
+// guaranteed to run in time linear in the size of the input.
+// (This is a property not guaranteed by most open source
+// implementations of regular expressions.) For more information
+// about this property, see
+//
+//	https://swtch.com/~rsc/regexp/regexp1.html
+//
+// or any book about automata theory.
+//
+// All characters are UTF-8-encoded code points.
+// Following [utf8.DecodeRune], each byte of an invalid UTF-8 sequence
+// is treated as if it encoded utf8.RuneError (U+FFFD).
+//
+// There are 16 methods of [Regexp] that match a regular expression and identify
+// the matched text. Their names are matched by this regular expression:
+//
+//	Find(All)?(String)?(Submatch)?(Index)?
+//
+// If 'All' is present, the routine matches successive non-overlapping
+// matches of the entire expression. Empty matches abutting a preceding
+// match are ignored. The return value is a slice containing the successive
+// return values of the corresponding non-'All' routine. These routines take
+// an extra integer argument, n. If n >= 0, the function returns at most n
+// matches/submatches; otherwise, it returns all of them.
+//
+// If 'String' is present, the argument is a string; otherwise it is a slice
+// of bytes; return values are adjusted as appropriate.
+//
+// If 'Submatch' is present, the return value is a slice identifying the
+// successive submatches of the expression. Submatches are matches of
+// parenthesized subexpressions (also known as capturing groups) within the
+// regular expression, numbered from left to right in order of opening
+// parenthesis. Submatch 0 is the match of the entire expression, submatch 1 is
+// the match of the first parenthesized subexpression, and so on.
+//
+// If 'Index' is present, matches and submatches are identified by byte index
+// pairs within the input string: result[2*n:2*n+2] identifies the indexes of
+// the nth submatch. The pair for n==0 identifies the match of the entire
+// expression. If 'Index' is not present, the match is identified by the text
+// of the match/submatch. If an index is negative or text is nil, it means that
+// subexpression did not match any string in the input. For 'String' versions
+// an empty string means either no match or an empty match.
+//
+// There is also a subset of the methods that can be applied to text read
+// from a RuneReader:
+//
+//	MatchReader, FindReaderIndex, FindReaderSubmatchIndex
+//
+// This set may grow. Note that regular expression matches may need to
+// examine text beyond the text returned by a match, so the methods that
+// match text from a RuneReader may read arbitrarily far into the input
+// before returning.
+//
+// (There are a few other methods that do not match this pattern.)
+package regexp
+
+import (
+	"bytes"
+	"io"
+	"regexp/syntax"
+	"strconv"
+	"strings"
+	"sync"
+	"unicode"
+	"unicode/utf8"
+)
+
+// Regexp is the representation of a compiled regular expression.
+// A Regexp is safe for concurrent use by multiple goroutines,
+// except for configuration methods, such as [Regexp.Longest].
+type Regexp struct {
+	expr           string       // as passed to Compile
+	prog           *syntax.Prog // compiled program
+	onepass        *onePassProg // onepass program or nil
+	numSubexp      int
+	maxBitStateLen int
+	subexpNames    []string
+	prefix         string         // required prefix in unanchored matches
+	prefixBytes    []byte         // prefix, as a []byte
+	prefixRune     rune           // first rune in prefix
+	prefixEnd      uint32         // pc for last rune in prefix
+	mpool          int            // pool for machines
+	matchcap       int            // size of recorded match lengths
+	prefixComplete bool           // prefix is the entire regexp
+	cond           syntax.EmptyOp // empty-width conditions required at start of match
+	minInputLen    int            // minimum length of the input in bytes
+
+	// This field can be modified by the Longest method,
+	// but it is otherwise read-only.
+	longest bool // whether regexp prefers leftmost-longest match
+}
+
+// String returns the source text used to compile the regular expression.
+func (re *Regexp) String() string {
+	return re.expr
+}
+
+// Copy returns a new [Regexp] object copied from re.
+// Calling [Regexp.Longest] on one copy does not affect another.
+//
+// Deprecated: In earlier releases, when using a [Regexp] in multiple goroutines,
+// giving each goroutine its own copy helped to avoid lock contention.
+// As of Go 1.12, using Copy is no longer necessary to avoid lock contention.
+// Copy may still be appropriate if the reason for its use is to make
+// two copies with different [Regexp.Longest] settings.
+func (re *Regexp) Copy() *Regexp {
+	re2 := *re
+	return &re2
+}
+
+// Compile parses a regular expression and returns, if successful,
+// a [Regexp] object that can be used to match against text.
+//
+// When matching against text, the regexp returns a match that
+// begins as early as possible in the input (leftmost), and among those
+// it chooses the one that a backtracking search would have found first.
+// This so-called leftmost-first matching is the same semantics
+// that Perl, Python, and other implementations use, although this
+// package implements it without the expense of backtracking.
+// For POSIX leftmost-longest matching, see [CompilePOSIX].
+func Compile(expr string) (*Regexp, error) {
+	return compile(expr, syntax.Perl, false)
+}
+
+// CompilePOSIX is like [Compile] but restricts the regular expression
+// to POSIX ERE (egrep) syntax and changes the match semantics to
+// leftmost-longest.
+//
+// That is, when matching against text, the regexp returns a match that
+// begins as early as possible in the input (leftmost), and among those
+// it chooses a match that is as long as possible.
+// This so-called leftmost-longest matching is the same semantics
+// that early regular expression implementations used and that POSIX
+// specifies.
+//
+// However, there can be multiple leftmost-longest matches, with different
+// submatch choices, and here this package diverges from POSIX.
+// Among the possible leftmost-longest matches, this package chooses
+// the one that a backtracking search would have found first, while POSIX
+// specifies that the match be chosen to maximize the length of the first
+// subexpression, then the second, and so on from left to right.
+// The POSIX rule is computationally prohibitive and not even well-defined.
+// See https://swtch.com/~rsc/regexp/regexp2.html#posix for details.
+func CompilePOSIX(expr string) (*Regexp, error) {
+	return compile(expr, syntax.POSIX, true)
+}
+
+// Longest makes future searches prefer the leftmost-longest match.
+// That is, when matching against text, the regexp returns a match that
+// begins as early as possible in the input (leftmost), and among those
+// it chooses a match that is as long as possible.
+// This method modifies the [Regexp] and may not be called concurrently
+// with any other methods.
+func (re *Regexp) Longest() {
+	re.longest = true
+}
+
+func compile(expr string, mode syntax.Flags, longest bool) (*Regexp, error) {
+	re, err := syntax.Parse(expr, mode)
+	if err != nil {
+		return nil, err
+	}
+	maxCap := re.MaxCap()
+	capNames := re.CapNames()
+
+	re = re.Simplify()
+	prog, err := syntax.Compile(re)
+	if err != nil {
+		return nil, err
+	}
+	matchcap := prog.NumCap
+	if matchcap < 2 {
+		matchcap = 2
+	}
+	regexp := &Regexp{
+		expr:        expr,
+		prog:        prog,
+		onepass:     compileOnePass(prog),
+		numSubexp:   maxCap,
+		subexpNames: capNames,
+		cond:        prog.StartCond(),
+		longest:     longest,
+		matchcap:    matchcap,
+		minInputLen: minInputLen(re),
+	}
+	if regexp.onepass == nil {
+		regexp.prefix, regexp.prefixComplete = prog.Prefix()
+		regexp.maxBitStateLen = maxBitStateLen(prog)
+	} else {
+		regexp.prefix, regexp.prefixComplete, regexp.prefixEnd = onePassPrefix(prog)
+	}
+	if regexp.prefix != "" {
+		// TODO(rsc): Remove this allocation by adding
+		// IndexString to package bytes.
+		regexp.prefixBytes = []byte(regexp.prefix)
+		regexp.prefixRune, _ = utf8.DecodeRuneInString(regexp.prefix)
+	}
+
+	n := len(prog.Inst)
+	i := 0
+	for matchSize[i] != 0 && matchSize[i] < n {
+		i++
+	}
+	regexp.mpool = i
+
+	return regexp, nil
+}
+
+// Pools of *machine for use during (*Regexp).doExecute,
+// split up by the size of the execution queues.
+// matchPool[i] machines have queue size matchSize[i].
+// On a 64-bit system each queue entry is 16 bytes,
+// so matchPool[0] has 16*2*128 = 4kB queues, etc.
+// The final matchPool is a catch-all for very large queues.
+var (
+	matchSize = [...]int{128, 512, 2048, 16384, 0}
+	matchPool [len(matchSize)]sync.Pool
+)
+
+// get returns a machine to use for matching re.
+// It uses the re's machine cache if possible, to avoid
+// unnecessary allocation.
+func (re *Regexp) get() *machine {
+	m, ok := matchPool[re.mpool].Get().(*machine)
+	if !ok {
+		m = new(machine)
+	}
+	m.re = re
+	m.p = re.prog
+	if cap(m.matchcap) < re.matchcap {
+		m.matchcap = make([]int, re.matchcap)
+		for _, t := range m.pool {
+			t.cap = make([]int, re.matchcap)
+		}
+	}
+
+	// Allocate queues if needed.
+	// Or reallocate, for "large" match pool.
+	n := matchSize[re.mpool]
+	if n == 0 { // large pool
+		n = len(re.prog.Inst)
+	}
+	if len(m.q0.sparse) < n {
+		m.q0 = queue{make([]uint32, n), make([]entry, 0, n)}
+		m.q1 = queue{make([]uint32, n), make([]entry, 0, n)}
+	}
+	return m
+}
+
+// put returns a machine to the correct machine pool.
+func (re *Regexp) put(m *machine) {
+	m.re = nil
+	m.p = nil
+	m.inputs.clear()
+	matchPool[re.mpool].Put(m)
+}
+
+// minInputLen walks the regexp to find the minimum length of any matchable input.
+func minInputLen(re *syntax.Regexp) int {
+	switch re.Op {
+	default:
+		return 0
+	case syntax.OpAnyChar, syntax.OpAnyCharNotNL, syntax.OpCharClass:
+		return 1
+	case syntax.OpLiteral:
+		l := 0
+		for _, r := range re.Rune {
+			if r == utf8.RuneError {
+				l++
+			} else {
+				l += utf8.RuneLen(r)
+			}
+		}
+		return l
+	case syntax.OpCapture, syntax.OpPlus:
+		return minInputLen(re.Sub[0])
+	case syntax.OpRepeat:
+		return re.Min * minInputLen(re.Sub[0])
+	case syntax.OpConcat:
+		l := 0
+		for _, sub := range re.Sub {
+			l += minInputLen(sub)
+		}
+		return l
+	case syntax.OpAlternate:
+		l := minInputLen(re.Sub[0])
+		var lnext int
+		for _, sub := range re.Sub[1:] {
+			lnext = minInputLen(sub)
+			if lnext < l {
+				l = lnext
+			}
+		}
+		return l
+	}
+}
+
+// MustCompile is like [Compile] but panics if the expression cannot be parsed.
+// It simplifies safe initialization of global variables holding compiled regular
+// expressions.
+func MustCompile(str string) *Regexp {
+	regexp, err := Compile(str)
+	if err != nil {
+		panic(`regexp: Compile(` + quote(str) + `): ` + err.Error())
+	}
+	return regexp
+}
+
+// MustCompilePOSIX is like [CompilePOSIX] but panics if the expression cannot be parsed.
+// It simplifies safe initialization of global variables holding compiled regular
+// expressions.
+func MustCompilePOSIX(str string) *Regexp {
+	regexp, err := CompilePOSIX(str)
+	if err != nil {
+		panic(`regexp: CompilePOSIX(` + quote(str) + `): ` + err.Error())
+	}
+	return regexp
+}
+
+func quote(s string) string {
+	if strconv.CanBackquote(s) {
+		return "`" + s + "`"
+	}
+	return strconv.Quote(s)
+}
+
+// NumSubexp returns the number of parenthesized subexpressions in this [Regexp].
+func (re *Regexp) NumSubexp() int {
+	return re.numSubexp
+}
+
+// SubexpNames returns the names of the parenthesized subexpressions
+// in this [Regexp]. The name for the first sub-expression is names[1],
+// so that if m is a match slice, the name for m[i] is SubexpNames()[i].
+// Since the Regexp as a whole cannot be named, names[0] is always
+// the empty string. The slice should not be modified.
+func (re *Regexp) SubexpNames() []string {
+	return re.subexpNames
+}
+
+// SubexpIndex returns the index of the first subexpression with the given name,
+// or -1 if there is no subexpression with that name.
+//
+// Note that multiple subexpressions can be written using the same name, as in
+// (?P<bob>a+)(?P<bob>b+), which declares two subexpressions named "bob".
+// In this case, SubexpIndex returns the index of the leftmost such subexpression
+// in the regular expression.
+func (re *Regexp) SubexpIndex(name string) int {
+	if name != "" {
+		for i, s := range re.subexpNames {
+			if name == s {
+				return i
+			}
+		}
+	}
+	return -1
+}
+
+const endOfText rune = -1
+
+// input abstracts different representations of the input text. It provides
+// one-character lookahead.
+type input interface {
+	step(pos int) (r rune, width int) // advance one rune
+	canCheckPrefix() bool             // can we look ahead without losing info?
+	hasPrefix(re *Regexp) bool
+	index(re *Regexp, pos int) int
+	context(pos int) lazyFlag
+}
+
+// inputString scans a string.
+type inputString struct {
+	str string
+}
+
+func (i *inputString) step(pos int) (rune, int) {
+	if pos < len(i.str) {
+		c := i.str[pos]
+		if c < utf8.RuneSelf {
+			return rune(c), 1
+		}
+		return utf8.DecodeRuneInString(i.str[pos:])
+	}
+	return endOfText, 0
+}
+
+func (i *inputString) canCheckPrefix() bool {
+	return true
+}
+
+func (i *inputString) hasPrefix(re *Regexp) bool {
+	return strings.HasPrefix(i.str, re.prefix)
+}
+
+func (i *inputString) index(re *Regexp, pos int) int {
+	return strings.Index(i.str[pos:], re.prefix)
+}
+
+func (i *inputString) context(pos int) lazyFlag {
+	r1, r2 := endOfText, endOfText
+	// 0 < pos && pos <= len(i.str)
+	if uint(pos-1) < uint(len(i.str)) {
+		r1 = rune(i.str[pos-1])
+		if r1 >= utf8.RuneSelf {
+			r1, _ = utf8.DecodeLastRuneInString(i.str[:pos])
+		}
+	}
+	// 0 <= pos && pos < len(i.str)
+	if uint(pos) < uint(len(i.str)) {
+		r2 = rune(i.str[pos])
+		if r2 >= utf8.RuneSelf {
+			r2, _ = utf8.DecodeRuneInString(i.str[pos:])
+		}
+	}
+	return newLazyFlag(r1, r2)
+}
+
+// inputBytes scans a byte slice.
+type inputBytes struct {
+	str []byte
+}
+
+func (i *inputBytes) step(pos int) (rune, int) {
+	if pos < len(i.str) {
+		c := i.str[pos]
+		if c < utf8.RuneSelf {
+			return rune(c), 1
+		}
+		return utf8.DecodeRune(i.str[pos:])
+	}
+	return endOfText, 0
+}
+
+func (i *inputBytes) canCheckPrefix() bool {
+	return true
+}
+
+func (i *inputBytes) hasPrefix(re *Regexp) bool {
+	return bytes.HasPrefix(i.str, re.prefixBytes)
+}
+
+func (i *inputBytes) index(re *Regexp, pos int) int {
+	return bytes.Index(i.str[pos:], re.prefixBytes)
+}
+
+func (i *inputBytes) context(pos int) lazyFlag {
+	r1, r2 := endOfText, endOfText
+	// 0 < pos && pos <= len(i.str)
+	if uint(pos-1) < uint(len(i.str)) {
+		r1 = rune(i.str[pos-1])
+		if r1 >= utf8.RuneSelf {
+			r1, _ = utf8.DecodeLastRune(i.str[:pos])
+		}
+	}
+	// 0 <= pos && pos < len(i.str)
+	if uint(pos) < uint(len(i.str)) {
+		r2 = rune(i.str[pos])
+		if r2 >= utf8.RuneSelf {
+			r2, _ = utf8.DecodeRune(i.str[pos:])
+		}
+	}
+	return newLazyFlag(r1, r2)
+}
+
+// inputReader scans a RuneReader.
+type inputReader struct {
+	r     io.RuneReader
+	atEOT bool
+	pos   int
+}
+
+func (i *inputReader) step(pos int) (rune, int) {
+	if !i.atEOT && pos != i.pos {
+		return endOfText, 0
+
+	}
+	r, w, err := i.r.ReadRune()
+	if err != nil {
+		i.atEOT = true
+		return endOfText, 0
+	}
+	i.pos += w
+	return r, w
+}
+
+func (i *inputReader) canCheckPrefix() bool {
+	return false
+}
+
+func (i *inputReader) hasPrefix(re *Regexp) bool {
+	return false
+}
+
+func (i *inputReader) index(re *Regexp, pos int) int {
+	return -1
+}
+
+func (i *inputReader) context(pos int) lazyFlag {
+	return 0 // not used
+}
+
+// LiteralPrefix returns a literal string that must begin any match
+// of the regular expression re. It returns the boolean true if the
+// literal string comprises the entire regular expression.
+func (re *Regexp) LiteralPrefix() (prefix string, complete bool) {
+	return re.prefix, re.prefixComplete
+}
+
+// MatchReader reports whether the text returned by the [io.RuneReader]
+// contains any match of the regular expression re.
+func (re *Regexp) MatchReader(r io.RuneReader) bool {
+	return re.doMatch(r, nil, "")
+}
+
+// MatchString reports whether the string s
+// contains any match of the regular expression re.
+func (re *Regexp) MatchString(s string) bool {
+	return re.doMatch(nil, nil, s)
+}
+
+// Match reports whether the byte slice b
+// contains any match of the regular expression re.
+func (re *Regexp) Match(b []byte) bool {
+	return re.doMatch(nil, b, "")
+}
+
+// MatchReader reports whether the text returned by the RuneReader
+// contains any match of the regular expression pattern.
+// More complicated queries need to use [Compile] and the full [Regexp] interface.
+func MatchReader(pattern string, r io.RuneReader) (matched bool, err error) {
+	re, err := Compile(pattern)
+	if err != nil {
+		return false, err
+	}
+	return re.MatchReader(r), nil
+}
+
+// MatchString reports whether the string s
+// contains any match of the regular expression pattern.
+// More complicated queries need to use [Compile] and the full [Regexp] interface.
+func MatchString(pattern string, s string) (matched bool, err error) {
+	re, err := Compile(pattern)
+	if err != nil {
+		return false, err
+	}
+	return re.MatchString(s), nil
+}
+
+// Match reports whether the byte slice b
+// contains any match of the regular expression pattern.
+// More complicated queries need to use [Compile] and the full [Regexp] interface.
+func Match(pattern string, b []byte) (matched bool, err error) {
+	re, err := Compile(pattern)
+	if err != nil {
+		return false, err
+	}
+	return re.Match(b), nil
+}
+
+// ReplaceAllString returns a copy of src, replacing matches of the [Regexp]
+// with the replacement string repl.
+// Inside repl, $ signs are interpreted as in [Regexp.Expand].
+func (re *Regexp) ReplaceAllString(src, repl string) string {
+	n := 2
+	if strings.Contains(repl, "$") {
+		n = 2 * (re.numSubexp + 1)
+	}
+	b := re.replaceAll(nil, src, n, func(dst []byte, match []int) []byte {
+		return re.expand(dst, repl, nil, src, match)
+	})
+	return string(b)
+}
+
+// ReplaceAllLiteralString returns a copy of src, replacing matches of the [Regexp]
+// with the replacement string repl. The replacement repl is substituted directly,
+// without using [Regexp.Expand].
+func (re *Regexp) ReplaceAllLiteralString(src, repl string) string {
+	return string(re.replaceAll(nil, src, 2, func(dst []byte, match []int) []byte {
+		return append(dst, repl...)
+	}))
+}
+
+// ReplaceAllStringFunc returns a copy of src in which all matches of the
+// [Regexp] have been replaced by the return value of function repl applied
+// to the matched substring. The replacement returned by repl is substituted
+// directly, without using [Regexp.Expand].
+func (re *Regexp) ReplaceAllStringFunc(src string, repl func(string) string) string {
+	b := re.replaceAll(nil, src, 2, func(dst []byte, match []int) []byte {
+		return append(dst, repl(src[match[0]:match[1]])...)
+	})
+	return string(b)
+}
+
+func (re *Regexp) replaceAll(bsrc []byte, src string, nmatch int, repl func(dst []byte, m []int) []byte) []byte {
+	lastMatchEnd := 0 // end position of the most recent match
+	searchPos := 0    // position where we next look for a match
+	var buf []byte
+	var endPos int
+	if bsrc != nil {
+		endPos = len(bsrc)
+	} else {
+		endPos = len(src)
+	}
+	if nmatch > re.prog.NumCap {
+		nmatch = re.prog.NumCap
+	}
+
+	var dstCap [2]int
+	for searchPos <= endPos {
+		a := re.doExecute(nil, bsrc, src, searchPos, nmatch, dstCap[:0])
+		if len(a) == 0 {
+			break // no more matches
+		}
+
+		// Copy the unmatched characters before this match.
+		if bsrc != nil {
+			buf = append(buf, bsrc[lastMatchEnd:a[0]]...)
+		} else {
+			buf = append(buf, src[lastMatchEnd:a[0]]...)
+		}
+
+		// Now insert a copy of the replacement string, but not for a
+		// match of the empty string immediately after another match.
+		// (Otherwise, we get double replacement for patterns that
+		// match both empty and nonempty strings.)
+		if a[1] > lastMatchEnd || a[0] == 0 {
+			buf = repl(buf, a)
+		}
+		lastMatchEnd = a[1]
+
+		// Advance past this match; always advance at least one character.
+		var width int
+		if bsrc != nil {
+			_, width = utf8.DecodeRune(bsrc[searchPos:])
+		} else {
+			_, width = utf8.DecodeRuneInString(src[searchPos:])
+		}
+		if searchPos+width > a[1] {
+			searchPos += width
+		} else if searchPos+1 > a[1] {
+			// This clause is only needed at the end of the input
+			// string. In that case, DecodeRuneInString returns width=0.
+			searchPos++
+		} else {
+			searchPos = a[1]
+		}
+	}
+
+	// Copy the unmatched characters after the last match.
+	if bsrc != nil {
+		buf = append(buf, bsrc[lastMatchEnd:]...)
+	} else {
+		buf = append(buf, src[lastMatchEnd:]...)
+	}
+
+	return buf
+}
+
+// ReplaceAll returns a copy of src, replacing matches of the [Regexp]
+// with the replacement text repl.
+// Inside repl, $ signs are interpreted as in [Regexp.Expand].
+func (re *Regexp) ReplaceAll(src, repl []byte) []byte {
+	n := 2
+	if bytes.IndexByte(repl, '$') >= 0 {
+		n = 2 * (re.numSubexp + 1)
+	}
+	srepl := ""
+	b := re.replaceAll(src, "", n, func(dst []byte, match []int) []byte {
+		if len(srepl) != len(repl) {
+			srepl = string(repl)
+		}
+		return re.expand(dst, srepl, src, "", match)
+	})
+	return b
+}
+
+// ReplaceAllLiteral returns a copy of src, replacing matches of the [Regexp]
+// with the replacement bytes repl. The replacement repl is substituted directly,
+// without using [Regexp.Expand].
+func (re *Regexp) ReplaceAllLiteral(src, repl []byte) []byte {
+	return re.replaceAll(src, "", 2, func(dst []byte, match []int) []byte {
+		return append(dst, repl...)
+	})
+}
+
+// ReplaceAllFunc returns a copy of src in which all matches of the
+// [Regexp] have been replaced by the return value of function repl applied
+// to the matched byte slice. The replacement returned by repl is substituted
+// directly, without using [Regexp.Expand].
+func (re *Regexp) ReplaceAllFunc(src []byte, repl func([]byte) []byte) []byte {
+	return re.replaceAll(src, "", 2, func(dst []byte, match []int) []byte {
+		return append(dst, repl(src[match[0]:match[1]])...)
+	})
+}
+
+// Bitmap used by func special to check whether a character needs to be escaped.
+var specialBytes [16]byte
+
+// special reports whether byte b needs to be escaped by QuoteMeta.
+func special(b byte) bool {
+	return b < utf8.RuneSelf && specialBytes[b%16]&(1<<(b/16)) != 0
+}
+
+func init() {
+	for _, b := range []byte(`\.+*?()|[]{}^$`) {
+		specialBytes[b%16] |= 1 << (b / 16)
+	}
+}
+
+// QuoteMeta returns a string that escapes all regular expression metacharacters
+// inside the argument text; the returned string is a regular expression matching
+// the literal text.
+func QuoteMeta(s string) string {
+	// A byte loop is correct because all metacharacters are ASCII.
+	var i int
+	for i = 0; i < len(s); i++ {
+		if special(s[i]) {
+			break
+		}
+	}
+	// No meta characters found, so return original string.
+	if i >= len(s) {
+		return s
+	}
+
+	b := make([]byte, 2*len(s)-i)
+	copy(b, s[:i])
+	j := i
+	for ; i < len(s); i++ {
+		if special(s[i]) {
+			b[j] = '\\'
+			j++
+		}
+		b[j] = s[i]
+		j++
+	}
+	return string(b[:j])
+}
+
+// The number of capture values in the program may correspond
+// to fewer capturing expressions than are in the regexp.
+// For example, "(a){0}" turns into an empty program, so the
+// maximum capture in the program is 0 but we need to return
+// an expression for \1.  Pad appends -1s to the slice a as needed.
+func (re *Regexp) pad(a []int) []int {
+	if a == nil {
+		// No match.
+		return nil
+	}
+	n := (1 + re.numSubexp) * 2
+	for len(a) < n {
+		a = append(a, -1)
+	}
+	return a
+}
+
+// allMatches calls deliver at most n times
+// with the location of successive matches in the input text.
+// The input text is b if non-nil, otherwise s.
+func (re *Regexp) allMatches(s string, b []byte, n int, deliver func([]int)) {
+	var end int
+	if b == nil {
+		end = len(s)
+	} else {
+		end = len(b)
+	}
+
+	for pos, i, prevMatchEnd := 0, 0, -1; i < n && pos <= end; {
+		matches := re.doExecute(nil, b, s, pos, re.prog.NumCap, nil)
+		if len(matches) == 0 {
+			break
+		}
+
+		accept := true
+		if matches[1] == pos {
+			// We've found an empty match.
+			if matches[0] == prevMatchEnd {
+				// We don't allow an empty match right
+				// after a previous match, so ignore it.
+				accept = false
+			}
+			var width int
+			if b == nil {
+				is := inputString{str: s}
+				_, width = is.step(pos)
+			} else {
+				ib := inputBytes{str: b}
+				_, width = ib.step(pos)
+			}
+			if width > 0 {
+				pos += width
+			} else {
+				pos = end + 1
+			}
+		} else {
+			pos = matches[1]
+		}
+		prevMatchEnd = matches[1]
+
+		if accept {
+			deliver(re.pad(matches))
+			i++
+		}
+	}
+}
+
+// Find returns a slice holding the text of the leftmost match in b of the regular expression.
+// A return value of nil indicates no match.
+func (re *Regexp) Find(b []byte) []byte {
+	var dstCap [2]int
+	a := re.doExecute(nil, b, "", 0, 2, dstCap[:0])
+	if a == nil {
+		return nil
+	}
+	return b[a[0]:a[1]:a[1]]
+}
+
+// FindIndex returns a two-element slice of integers defining the location of
+// the leftmost match in b of the regular expression. The match itself is at
+// b[loc[0]:loc[1]].
+// A return value of nil indicates no match.
+func (re *Regexp) FindIndex(b []byte) (loc []int) {
+	a := re.doExecute(nil, b, "", 0, 2, nil)
+	if a == nil {
+		return nil
+	}
+	return a[0:2]
+}
+
+// FindString returns a string holding the text of the leftmost match in s of the regular
+// expression. If there is no match, the return value is an empty string,
+// but it will also be empty if the regular expression successfully matches
+// an empty string. Use [Regexp.FindStringIndex] or [Regexp.FindStringSubmatch] if it is
+// necessary to distinguish these cases.
+func (re *Regexp) FindString(s string) string {
+	var dstCap [2]int
+	a := re.doExecute(nil, nil, s, 0, 2, dstCap[:0])
+	if a == nil {
+		return ""
+	}
+	return s[a[0]:a[1]]
+}
+
+// FindStringIndex returns a two-element slice of integers defining the
+// location of the leftmost match in s of the regular expression. The match
+// itself is at s[loc[0]:loc[1]].
+// A return value of nil indicates no match.
+func (re *Regexp) FindStringIndex(s string) (loc []int) {
+	a := re.doExecute(nil, nil, s, 0, 2, nil)
+	if a == nil {
+		return nil
+	}
+	return a[0:2]
+}
+
+// FindReaderIndex returns a two-element slice of integers defining the
+// location of the leftmost match of the regular expression in text read from
+// the [io.RuneReader]. The match text was found in the input stream at
+// byte offset loc[0] through loc[1]-1.
+// A return value of nil indicates no match.
+func (re *Regexp) FindReaderIndex(r io.RuneReader) (loc []int) {
+	a := re.doExecute(r, nil, "", 0, 2, nil)
+	if a == nil {
+		return nil
+	}
+	return a[0:2]
+}
+
+// FindSubmatch returns a slice of slices holding the text of the leftmost
+// match of the regular expression in b and the matches, if any, of its
+// subexpressions, as defined by the 'Submatch' descriptions in the package
+// comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindSubmatch(b []byte) [][]byte {
+	var dstCap [4]int
+	a := re.doExecute(nil, b, "", 0, re.prog.NumCap, dstCap[:0])
+	if a == nil {
+		return nil
+	}
+	ret := make([][]byte, 1+re.numSubexp)
+	for i := range ret {
+		if 2*i < len(a) && a[2*i] >= 0 {
+			ret[i] = b[a[2*i]:a[2*i+1]:a[2*i+1]]
+		}
+	}
+	return ret
+}
+
+// Expand appends template to dst and returns the result; during the
+// append, Expand replaces variables in the template with corresponding
+// matches drawn from src. The match slice should have been returned by
+// [Regexp.FindSubmatchIndex].
+//
+// In the template, a variable is denoted by a substring of the form
+// $name or ${name}, where name is a non-empty sequence of letters,
+// digits, and underscores. A purely numeric name like $1 refers to
+// the submatch with the corresponding index; other names refer to
+// capturing parentheses named with the (?P<name>...) syntax. A
+// reference to an out of range or unmatched index or a name that is not
+// present in the regular expression is replaced with an empty slice.
+//
+// In the $name form, name is taken to be as long as possible: $1x is
+// equivalent to ${1x}, not ${1}x, and, $10 is equivalent to ${10}, not ${1}0.
+//
+// To insert a literal $ in the output, use $$ in the template.
+func (re *Regexp) Expand(dst []byte, template []byte, src []byte, match []int) []byte {
+	return re.expand(dst, string(template), src, "", match)
+}
+
+// ExpandString is like [Regexp.Expand] but the template and source are strings.
+// It appends to and returns a byte slice in order to give the calling
+// code control over allocation.
+func (re *Regexp) ExpandString(dst []byte, template string, src string, match []int) []byte {
+	return re.expand(dst, template, nil, src, match)
+}
+
+func (re *Regexp) expand(dst []byte, template string, bsrc []byte, src string, match []int) []byte {
+	for len(template) > 0 {
+		before, after, ok := strings.Cut(template, "$")
+		if !ok {
+			break
+		}
+		dst = append(dst, before...)
+		template = after
+		if template != "" && template[0] == '$' {
+			// Treat $$ as $.
+			dst = append(dst, '$')
+			template = template[1:]
+			continue
+		}
+		name, num, rest, ok := extract(template)
+		if !ok {
+			// Malformed; treat $ as raw text.
+			dst = append(dst, '$')
+			continue
+		}
+		template = rest
+		if num >= 0 {
+			if 2*num+1 < len(match) && match[2*num] >= 0 {
+				if bsrc != nil {
+					dst = append(dst, bsrc[match[2*num]:match[2*num+1]]...)
+				} else {
+					dst = append(dst, src[match[2*num]:match[2*num+1]]...)
+				}
+			}
+		} else {
+			for i, namei := range re.subexpNames {
+				if name == namei && 2*i+1 < len(match) && match[2*i] >= 0 {
+					if bsrc != nil {
+						dst = append(dst, bsrc[match[2*i]:match[2*i+1]]...)
+					} else {
+						dst = append(dst, src[match[2*i]:match[2*i+1]]...)
+					}
+					break
+				}
+			}
+		}
+	}
+	dst = append(dst, template...)
+	return dst
+}
+
+// extract returns the name from a leading "name" or "{name}" in str.
+// (The $ has already been removed by the caller.)
+// If it is a number, extract returns num set to that number; otherwise num = -1.
+func extract(str string) (name string, num int, rest string, ok bool) {
+	if str == "" {
+		return
+	}
+	brace := false
+	if str[0] == '{' {
+		brace = true
+		str = str[1:]
+	}
+	i := 0
+	for i < len(str) {
+		rune, size := utf8.DecodeRuneInString(str[i:])
+		if !unicode.IsLetter(rune) && !unicode.IsDigit(rune) && rune != '_' {
+			break
+		}
+		i += size
+	}
+	if i == 0 {
+		// empty name is not okay
+		return
+	}
+	name = str[:i]
+	if brace {
+		if i >= len(str) || str[i] != '}' {
+			// missing closing brace
+			return
+		}
+		i++
+	}
+
+	// Parse number.
+	num = 0
+	for i := 0; i < len(name); i++ {
+		if name[i] < '0' || '9' < name[i] || num >= 1e8 {
+			num = -1
+			break
+		}
+		num = num*10 + int(name[i]) - '0'
+	}
+	// Disallow leading zeros.
+	if name[0] == '0' && len(name) > 1 {
+		num = -1
+	}
+
+	rest = str[i:]
+	ok = true
+	return
+}
+
+// FindSubmatchIndex returns a slice holding the index pairs identifying the
+// leftmost match of the regular expression in b and the matches, if any, of
+// its subexpressions, as defined by the 'Submatch' and 'Index' descriptions
+// in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindSubmatchIndex(b []byte) []int {
+	return re.pad(re.doExecute(nil, b, "", 0, re.prog.NumCap, nil))
+}
+
+// FindStringSubmatch returns a slice of strings holding the text of the
+// leftmost match of the regular expression in s and the matches, if any, of
+// its subexpressions, as defined by the 'Submatch' description in the
+// package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindStringSubmatch(s string) []string {
+	var dstCap [4]int
+	a := re.doExecute(nil, nil, s, 0, re.prog.NumCap, dstCap[:0])
+	if a == nil {
+		return nil
+	}
+	ret := make([]string, 1+re.numSubexp)
+	for i := range ret {
+		if 2*i < len(a) && a[2*i] >= 0 {
+			ret[i] = s[a[2*i]:a[2*i+1]]
+		}
+	}
+	return ret
+}
+
+// FindStringSubmatchIndex returns a slice holding the index pairs
+// identifying the leftmost match of the regular expression in s and the
+// matches, if any, of its subexpressions, as defined by the 'Submatch' and
+// 'Index' descriptions in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindStringSubmatchIndex(s string) []int {
+	return re.pad(re.doExecute(nil, nil, s, 0, re.prog.NumCap, nil))
+}
+
+// FindReaderSubmatchIndex returns a slice holding the index pairs
+// identifying the leftmost match of the regular expression of text read by
+// the [io.RuneReader], and the matches, if any, of its subexpressions, as defined
+// by the 'Submatch' and 'Index' descriptions in the package comment. A
+// return value of nil indicates no match.
+func (re *Regexp) FindReaderSubmatchIndex(r io.RuneReader) []int {
+	return re.pad(re.doExecute(r, nil, "", 0, re.prog.NumCap, nil))
+}
+
+const startSize = 10 // The size at which to start a slice in the 'All' routines.
+
+// FindAll is the 'All' version of Find; it returns a slice of all successive
+// matches of the expression, as defined by the 'All' description in the
+// package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAll(b []byte, n int) [][]byte {
+	if n < 0 {
+		n = len(b) + 1
+	}
+	var result [][]byte
+	re.allMatches("", b, n, func(match []int) {
+		if result == nil {
+			result = make([][]byte, 0, startSize)
+		}
+		result = append(result, b[match[0]:match[1]:match[1]])
+	})
+	return result
+}
+
+// FindAllIndex is the 'All' version of [Regexp.FindIndex]; it returns a slice of all
+// successive matches of the expression, as defined by the 'All' description
+// in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllIndex(b []byte, n int) [][]int {
+	if n < 0 {
+		n = len(b) + 1
+	}
+	var result [][]int
+	re.allMatches("", b, n, func(match []int) {
+		if result == nil {
+			result = make([][]int, 0, startSize)
+		}
+		result = append(result, match[0:2])
+	})
+	return result
+}
+
+// FindAllString is the 'All' version of [Regexp.FindString]; it returns a slice of all
+// successive matches of the expression, as defined by the 'All' description
+// in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllString(s string, n int) []string {
+	if n < 0 {
+		n = len(s) + 1
+	}
+	var result []string
+	re.allMatches(s, nil, n, func(match []int) {
+		if result == nil {
+			result = make([]string, 0, startSize)
+		}
+		result = append(result, s[match[0]:match[1]])
+	})
+	return result
+}
+
+// FindAllStringIndex is the 'All' version of [Regexp.FindStringIndex]; it returns a
+// slice of all successive matches of the expression, as defined by the 'All'
+// description in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllStringIndex(s string, n int) [][]int {
+	if n < 0 {
+		n = len(s) + 1
+	}
+	var result [][]int
+	re.allMatches(s, nil, n, func(match []int) {
+		if result == nil {
+			result = make([][]int, 0, startSize)
+		}
+		result = append(result, match[0:2])
+	})
+	return result
+}
+
+// FindAllSubmatch is the 'All' version of [Regexp.FindSubmatch]; it returns a slice
+// of all successive matches of the expression, as defined by the 'All'
+// description in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllSubmatch(b []byte, n int) [][][]byte {
+	if n < 0 {
+		n = len(b) + 1
+	}
+	var result [][][]byte
+	re.allMatches("", b, n, func(match []int) {
+		if result == nil {
+			result = make([][][]byte, 0, startSize)
+		}
+		slice := make([][]byte, len(match)/2)
+		for j := range slice {
+			if match[2*j] >= 0 {
+				slice[j] = b[match[2*j]:match[2*j+1]:match[2*j+1]]
+			}
+		}
+		result = append(result, slice)
+	})
+	return result
+}
+
+// FindAllSubmatchIndex is the 'All' version of [Regexp.FindSubmatchIndex]; it returns
+// a slice of all successive matches of the expression, as defined by the
+// 'All' description in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllSubmatchIndex(b []byte, n int) [][]int {
+	if n < 0 {
+		n = len(b) + 1
+	}
+	var result [][]int
+	re.allMatches("", b, n, func(match []int) {
+		if result == nil {
+			result = make([][]int, 0, startSize)
+		}
+		result = append(result, match)
+	})
+	return result
+}
+
+// FindAllStringSubmatch is the 'All' version of [Regexp.FindStringSubmatch]; it
+// returns a slice of all successive matches of the expression, as defined by
+// the 'All' description in the package comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllStringSubmatch(s string, n int) [][]string {
+	if n < 0 {
+		n = len(s) + 1
+	}
+	var result [][]string
+	re.allMatches(s, nil, n, func(match []int) {
+		if result == nil {
+			result = make([][]string, 0, startSize)
+		}
+		slice := make([]string, len(match)/2)
+		for j := range slice {
+			if match[2*j] >= 0 {
+				slice[j] = s[match[2*j]:match[2*j+1]]
+			}
+		}
+		result = append(result, slice)
+	})
+	return result
+}
+
+// FindAllStringSubmatchIndex is the 'All' version of
+// [Regexp.FindStringSubmatchIndex]; it returns a slice of all successive matches of
+// the expression, as defined by the 'All' description in the package
+// comment.
+// A return value of nil indicates no match.
+func (re *Regexp) FindAllStringSubmatchIndex(s string, n int) [][]int {
+	if n < 0 {
+		n = len(s) + 1
+	}
+	var result [][]int
+	re.allMatches(s, nil, n, func(match []int) {
+		if result == nil {
+			result = make([][]int, 0, startSize)
+		}
+		result = append(result, match)
+	})
+	return result
+}
+
+// Split slices s into substrings separated by the expression and returns a slice of
+// the substrings between those expression matches.
+//
+// The slice returned by this method consists of all the substrings of s
+// not contained in the slice returned by [Regexp.FindAllString]. When called on an expression
+// that contains no metacharacters, it is equivalent to [strings.SplitN].
+//
+// Example:
+//
+//	s := regexp.MustCompile("a*").Split("abaabaccadaaae", 5)
+//	// s: ["", "b", "b", "c", "cadaaae"]
+//
+// The count determines the number of substrings to return:
+//
+//	n > 0: at most n substrings; the last substring will be the unsplit remainder.
+//	n == 0: the result is nil (zero substrings)
+//	n < 0: all substrings
+func (re *Regexp) Split(s string, n int) []string {
+
+	if n == 0 {
+		return nil
+	}
+
+	if len(re.expr) > 0 && len(s) == 0 {
+		return []string{""}
+	}
+
+	matches := re.FindAllStringIndex(s, n)
+	strings := make([]string, 0, len(matches))
+
+	beg := 0
+	end := 0
+	for _, match := range matches {
+		if n > 0 && len(strings) >= n-1 {
+			break
+		}
+
+		end = match[0]
+		if match[1] != 0 {
+			strings = append(strings, s[beg:end])
+		}
+		beg = match[1]
+	}
+
+	if end != len(s) {
+		strings = append(strings, s[beg:])
+	}
+
+	return strings
+}
+
+// MarshalText implements [encoding.TextMarshaler]. The output
+// matches that of calling the [Regexp.String] method.
+//
+// Note that the output is lossy in some cases: This method does not indicate
+// POSIX regular expressions (i.e. those compiled by calling [CompilePOSIX]), or
+// those for which the [Regexp.Longest] method has been called.
+func (re *Regexp) MarshalText() ([]byte, error) {
+	return []byte(re.String()), nil
+}
+
+// UnmarshalText implements [encoding.TextUnmarshaler] by calling
+// [Compile] on the encoded value.
+func (re *Regexp) UnmarshalText(text []byte) error {
+	newRE, err := Compile(string(text))
+	if err != nil {
+		return err
+	}
+	*re = *newRE
+	return nil
+}
diff --git a/src/regexp/syntax/compile.go b/src/regexp/syntax/compile.go
new file mode 100644
index 0000000..c9f9fa0
--- /dev/null
+++ b/src/regexp/syntax/compile.go
@@ -0,0 +1,296 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+import "unicode"
+
+// A patchList is a list of instruction pointers that need to be filled in (patched).
+// Because the pointers haven't been filled in yet, we can reuse their storage
+// to hold the list. It's kind of sleazy, but works well in practice.
+// See https://swtch.com/~rsc/regexp/regexp1.html for inspiration.
+//
+// These aren't really pointers: they're integers, so we can reinterpret them
+// this way without using package unsafe. A value l.head denotes
+// p.inst[l.head>>1].Out (l.head&1==0) or .Arg (l.head&1==1).
+// head == 0 denotes the empty list, okay because we start every program
+// with a fail instruction, so we'll never want to point at its output link.
+type patchList struct {
+	head, tail uint32
+}
+
+func makePatchList(n uint32) patchList {
+	return patchList{n, n}
+}
+
+func (l patchList) patch(p *Prog, val uint32) {
+	head := l.head
+	for head != 0 {
+		i := &p.Inst[head>>1]
+		if head&1 == 0 {
+			head = i.Out
+			i.Out = val
+		} else {
+			head = i.Arg
+			i.Arg = val
+		}
+	}
+}
+
+func (l1 patchList) append(p *Prog, l2 patchList) patchList {
+	if l1.head == 0 {
+		return l2
+	}
+	if l2.head == 0 {
+		return l1
+	}
+
+	i := &p.Inst[l1.tail>>1]
+	if l1.tail&1 == 0 {
+		i.Out = l2.head
+	} else {
+		i.Arg = l2.head
+	}
+	return patchList{l1.head, l2.tail}
+}
+
+// A frag represents a compiled program fragment.
+type frag struct {
+	i        uint32    // index of first instruction
+	out      patchList // where to record end instruction
+	nullable bool      // whether fragment can match empty string
+}
+
+type compiler struct {
+	p *Prog
+}
+
+// Compile compiles the regexp into a program to be executed.
+// The regexp should have been simplified already (returned from re.Simplify).
+func Compile(re *Regexp) (*Prog, error) {
+	var c compiler
+	c.init()
+	f := c.compile(re)
+	f.out.patch(c.p, c.inst(InstMatch).i)
+	c.p.Start = int(f.i)
+	return c.p, nil
+}
+
+func (c *compiler) init() {
+	c.p = new(Prog)
+	c.p.NumCap = 2 // implicit ( and ) for whole match $0
+	c.inst(InstFail)
+}
+
+var anyRuneNotNL = []rune{0, '\n' - 1, '\n' + 1, unicode.MaxRune}
+var anyRune = []rune{0, unicode.MaxRune}
+
+func (c *compiler) compile(re *Regexp) frag {
+	switch re.Op {
+	case OpNoMatch:
+		return c.fail()
+	case OpEmptyMatch:
+		return c.nop()
+	case OpLiteral:
+		if len(re.Rune) == 0 {
+			return c.nop()
+		}
+		var f frag
+		for j := range re.Rune {
+			f1 := c.rune(re.Rune[j:j+1], re.Flags)
+			if j == 0 {
+				f = f1
+			} else {
+				f = c.cat(f, f1)
+			}
+		}
+		return f
+	case OpCharClass:
+		return c.rune(re.Rune, re.Flags)
+	case OpAnyCharNotNL:
+		return c.rune(anyRuneNotNL, 0)
+	case OpAnyChar:
+		return c.rune(anyRune, 0)
+	case OpBeginLine:
+		return c.empty(EmptyBeginLine)
+	case OpEndLine:
+		return c.empty(EmptyEndLine)
+	case OpBeginText:
+		return c.empty(EmptyBeginText)
+	case OpEndText:
+		return c.empty(EmptyEndText)
+	case OpWordBoundary:
+		return c.empty(EmptyWordBoundary)
+	case OpNoWordBoundary:
+		return c.empty(EmptyNoWordBoundary)
+	case OpCapture:
+		bra := c.cap(uint32(re.Cap << 1))
+		sub := c.compile(re.Sub[0])
+		ket := c.cap(uint32(re.Cap<<1 | 1))
+		return c.cat(c.cat(bra, sub), ket)
+	case OpStar:
+		return c.star(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpPlus:
+		return c.plus(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpQuest:
+		return c.quest(c.compile(re.Sub[0]), re.Flags&NonGreedy != 0)
+	case OpConcat:
+		if len(re.Sub) == 0 {
+			return c.nop()
+		}
+		var f frag
+		for i, sub := range re.Sub {
+			if i == 0 {
+				f = c.compile(sub)
+			} else {
+				f = c.cat(f, c.compile(sub))
+			}
+		}
+		return f
+	case OpAlternate:
+		var f frag
+		for _, sub := range re.Sub {
+			f = c.alt(f, c.compile(sub))
+		}
+		return f
+	}
+	panic("regexp: unhandled case in compile")
+}
+
+func (c *compiler) inst(op InstOp) frag {
+	// TODO: impose length limit
+	f := frag{i: uint32(len(c.p.Inst)), nullable: true}
+	c.p.Inst = append(c.p.Inst, Inst{Op: op})
+	return f
+}
+
+func (c *compiler) nop() frag {
+	f := c.inst(InstNop)
+	f.out = makePatchList(f.i << 1)
+	return f
+}
+
+func (c *compiler) fail() frag {
+	return frag{}
+}
+
+func (c *compiler) cap(arg uint32) frag {
+	f := c.inst(InstCapture)
+	f.out = makePatchList(f.i << 1)
+	c.p.Inst[f.i].Arg = arg
+
+	if c.p.NumCap < int(arg)+1 {
+		c.p.NumCap = int(arg) + 1
+	}
+	return f
+}
+
+func (c *compiler) cat(f1, f2 frag) frag {
+	// concat of failure is failure
+	if f1.i == 0 || f2.i == 0 {
+		return frag{}
+	}
+
+	// TODO: elide nop
+
+	f1.out.patch(c.p, f2.i)
+	return frag{f1.i, f2.out, f1.nullable && f2.nullable}
+}
+
+func (c *compiler) alt(f1, f2 frag) frag {
+	// alt of failure is other
+	if f1.i == 0 {
+		return f2
+	}
+	if f2.i == 0 {
+		return f1
+	}
+
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	i.Out = f1.i
+	i.Arg = f2.i
+	f.out = f1.out.append(c.p, f2.out)
+	f.nullable = f1.nullable || f2.nullable
+	return f
+}
+
+func (c *compiler) quest(f1 frag, nongreedy bool) frag {
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	if nongreedy {
+		i.Arg = f1.i
+		f.out = makePatchList(f.i << 1)
+	} else {
+		i.Out = f1.i
+		f.out = makePatchList(f.i<<1 | 1)
+	}
+	f.out = f.out.append(c.p, f1.out)
+	return f
+}
+
+// loop returns the fragment for the main loop of a plus or star.
+// For plus, it can be used after changing the entry to f1.i.
+// For star, it can be used directly when f1 can't match an empty string.
+// (When f1 can match an empty string, f1* must be implemented as (f1+)?
+// to get the priority match order correct.)
+func (c *compiler) loop(f1 frag, nongreedy bool) frag {
+	f := c.inst(InstAlt)
+	i := &c.p.Inst[f.i]
+	if nongreedy {
+		i.Arg = f1.i
+		f.out = makePatchList(f.i << 1)
+	} else {
+		i.Out = f1.i
+		f.out = makePatchList(f.i<<1 | 1)
+	}
+	f1.out.patch(c.p, f.i)
+	return f
+}
+
+func (c *compiler) star(f1 frag, nongreedy bool) frag {
+	if f1.nullable {
+		// Use (f1+)? to get priority match order correct.
+		// See golang.org/issue/46123.
+		return c.quest(c.plus(f1, nongreedy), nongreedy)
+	}
+	return c.loop(f1, nongreedy)
+}
+
+func (c *compiler) plus(f1 frag, nongreedy bool) frag {
+	return frag{f1.i, c.loop(f1, nongreedy).out, f1.nullable}
+}
+
+func (c *compiler) empty(op EmptyOp) frag {
+	f := c.inst(InstEmptyWidth)
+	c.p.Inst[f.i].Arg = uint32(op)
+	f.out = makePatchList(f.i << 1)
+	return f
+}
+
+func (c *compiler) rune(r []rune, flags Flags) frag {
+	f := c.inst(InstRune)
+	f.nullable = false
+	i := &c.p.Inst[f.i]
+	i.Rune = r
+	flags &= FoldCase // only relevant flag is FoldCase
+	if len(r) != 1 || unicode.SimpleFold(r[0]) == r[0] {
+		// and sometimes not even that
+		flags &^= FoldCase
+	}
+	i.Arg = uint32(flags)
+	f.out = makePatchList(f.i << 1)
+
+	// Special cases for exec machine.
+	switch {
+	case flags&FoldCase == 0 && (len(r) == 1 || len(r) == 2 && r[0] == r[1]):
+		i.Op = InstRune1
+	case len(r) == 2 && r[0] == 0 && r[1] == unicode.MaxRune:
+		i.Op = InstRuneAny
+	case len(r) == 4 && r[0] == 0 && r[1] == '\n'-1 && r[2] == '\n'+1 && r[3] == unicode.MaxRune:
+		i.Op = InstRuneAnyNotNL
+	}
+
+	return f
+}
diff --git a/src/regexp/syntax/doc.go b/src/regexp/syntax/doc.go
new file mode 100644
index 0000000..eb8a971
--- /dev/null
+++ b/src/regexp/syntax/doc.go
@@ -0,0 +1,142 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// DO NOT EDIT. This file is generated by mksyntaxgo from the RE2 distribution.
+
+/*
+Package syntax parses regular expressions into parse trees and compiles
+parse trees into programs. Most clients of regular expressions will use the
+facilities of package regexp (such as Compile and Match) instead of this package.
+
+# Syntax
+
+The regular expression syntax understood by this package when parsing with the Perl flag is as follows.
+Parts of the syntax can be disabled by passing alternate flags to Parse.
+
+Single characters:
+
+	.              any character, possibly including newline (flag s=true)
+	[xyz]          character class
+	[^xyz]         negated character class
+	\d             Perl character class
+	\D             negated Perl character class
+	[[:alpha:]]    ASCII character class
+	[[:^alpha:]]   negated ASCII character class
+	\pN            Unicode character class (one-letter name)
+	\p{Greek}      Unicode character class
+	\PN            negated Unicode character class (one-letter name)
+	\P{Greek}      negated Unicode character class
+
+Composites:
+
+	xy             x followed by y
+	x|y            x or y (prefer x)
+
+Repetitions:
+
+	x*             zero or more x, prefer more
+	x+             one or more x, prefer more
+	x?             zero or one x, prefer one
+	x{n,m}         n or n+1 or ... or m x, prefer more
+	x{n,}          n or more x, prefer more
+	x{n}           exactly n x
+	x*?            zero or more x, prefer fewer
+	x+?            one or more x, prefer fewer
+	x??            zero or one x, prefer zero
+	x{n,m}?        n or n+1 or ... or m x, prefer fewer
+	x{n,}?         n or more x, prefer fewer
+	x{n}?          exactly n x
+
+Implementation restriction: The counting forms x{n,m}, x{n,}, and x{n}
+reject forms that create a minimum or maximum repetition count above 1000.
+Unlimited repetitions are not subject to this restriction.
+
+Grouping:
+
+	(re)           numbered capturing group (submatch)
+	(?P<name>re)   named & numbered capturing group (submatch)
+	(?<name>re)    named & numbered capturing group (submatch)
+	(?:re)         non-capturing group
+	(?flags)       set flags within current group; non-capturing
+	(?flags:re)    set flags during re; non-capturing
+
+	Flag syntax is xyz (set) or -xyz (clear) or xy-z (set xy, clear z). The flags are:
+
+	i              case-insensitive (default false)
+	m              multi-line mode: ^ and $ match begin/end line in addition to begin/end text (default false)
+	s              let . match \n (default false)
+	U              ungreedy: swap meaning of x* and x*?, x+ and x+?, etc (default false)
+
+Empty strings:
+
+	^              at beginning of text or line (flag m=true)
+	$              at end of text (like \z not \Z) or line (flag m=true)
+	\A             at beginning of text
+	\b             at ASCII word boundary (\w on one side and \W, \A, or \z on the other)
+	\B             not at ASCII word boundary
+	\z             at end of text
+
+Escape sequences:
+
+	\a             bell (== \007)
+	\f             form feed (== \014)
+	\t             horizontal tab (== \011)
+	\n             newline (== \012)
+	\r             carriage return (== \015)
+	\v             vertical tab character (== \013)
+	\*             literal *, for any punctuation character *
+	\123           octal character code (up to three digits)
+	\x7F           hex character code (exactly two digits)
+	\x{10FFFF}     hex character code
+	\Q...\E        literal text ... even if ... has punctuation
+
+Character class elements:
+
+	x              single character
+	A-Z            character range (inclusive)
+	\d             Perl character class
+	[:foo:]        ASCII character class foo
+	\p{Foo}        Unicode character class Foo
+	\pF            Unicode character class F (one-letter name)
+
+Named character classes as character class elements:
+
+	[\d]           digits (== \d)
+	[^\d]          not digits (== \D)
+	[\D]           not digits (== \D)
+	[^\D]          not not digits (== \d)
+	[[:name:]]     named ASCII class inside character class (== [:name:])
+	[^[:name:]]    named ASCII class inside negated character class (== [:^name:])
+	[\p{Name}]     named Unicode property inside character class (== \p{Name})
+	[^\p{Name}]    named Unicode property inside negated character class (== \P{Name})
+
+Perl character classes (all ASCII-only):
+
+	\d             digits (== [0-9])
+	\D             not digits (== [^0-9])
+	\s             whitespace (== [\t\n\f\r ])
+	\S             not whitespace (== [^\t\n\f\r ])
+	\w             word characters (== [0-9A-Za-z_])
+	\W             not word characters (== [^0-9A-Za-z_])
+
+ASCII character classes:
+
+	[[:alnum:]]    alphanumeric (== [0-9A-Za-z])
+	[[:alpha:]]    alphabetic (== [A-Za-z])
+	[[:ascii:]]    ASCII (== [\x00-\x7F])
+	[[:blank:]]    blank (== [\t ])
+	[[:cntrl:]]    control (== [\x00-\x1F\x7F])
+	[[:digit:]]    digits (== [0-9])
+	[[:graph:]]    graphical (== [!-~] == [A-Za-z0-9!"#$%&'()*+,\-./:;<=>?@[\\\]^_`{|}~])
+	[[:lower:]]    lower case (== [a-z])
+	[[:print:]]    printable (== [ -~] == [ [:graph:]])
+	[[:punct:]]    punctuation (== [!-/:-@[-`{-~])
+	[[:space:]]    whitespace (== [\t\n\v\f\r ])
+	[[:upper:]]    upper case (== [A-Z])
+	[[:word:]]     word characters (== [0-9A-Za-z_])
+	[[:xdigit:]]   hex digit (== [0-9A-Fa-f])
+
+Unicode character classes are those in unicode.Categories and unicode.Scripts.
+*/
+package syntax
diff --git a/src/regexp/syntax/make_perl_groups.pl b/src/regexp/syntax/make_perl_groups.pl
new file mode 100755
index 0000000..80a2c9a
--- /dev/null
+++ b/src/regexp/syntax/make_perl_groups.pl
@@ -0,0 +1,113 @@
+#!/usr/bin/perl
+# Copyright 2008 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+# Modified version of RE2's make_perl_groups.pl.
+
+# Generate table entries giving character ranges
+# for POSIX/Perl character classes.  Rather than
+# figure out what the definition is, it is easier to ask
+# Perl about each letter from 0-128 and write down
+# its answer.
+
+@posixclasses = (
+	"[:alnum:]",
+	"[:alpha:]",
+	"[:ascii:]",
+	"[:blank:]",
+	"[:cntrl:]",
+	"[:digit:]",
+	"[:graph:]",
+	"[:lower:]",
+	"[:print:]",
+	"[:punct:]",
+	"[:space:]",
+	"[:upper:]",
+	"[:word:]",
+	"[:xdigit:]",
+);
+
+@perlclasses = (
+	"\\d",
+	"\\s",
+	"\\w",
+);
+
+%overrides = (
+	# Prior to Perl 5.18, \s did not match vertical tab.
+	# RE2 preserves that original behaviour.
+	"\\s:11" => 0,
+);
+
+sub ComputeClass($) {
+  my @ranges;
+  my ($class) = @_;
+  my $regexp = "[$class]";
+  my $start = -1;
+  for (my $i=0; $i<=129; $i++) {
+    if ($i == 129) { $i = 256; }
+    if ($i <= 128 && ($overrides{"$class:$i"} // chr($i) =~ $regexp)) {
+      if ($start < 0) {
+        $start = $i;
+      }
+    } else {
+      if ($start >= 0) {
+        push @ranges, [$start, $i-1];
+      }
+      $start = -1;
+    }
+  }
+  return @ranges;
+}
+
+sub PrintClass($$@) {
+  my ($cname, $name, @ranges) = @_;
+  print "var code$cname = []rune{  /* $name */\n";
+  for (my $i=0; $i<@ranges; $i++) {
+    my @a = @{$ranges[$i]};
+    printf "\t0x%x, 0x%x,\n", $a[0], $a[1];
+  }
+  print "}\n\n";
+  my $n = @ranges;
+  $negname = $name;
+  if ($negname =~ /:/) {
+    $negname =~ s/:/:^/;
+  } else {
+    $negname =~ y/a-z/A-Z/;
+  }
+  return "\t`$name`: {+1, code$cname},\n" .
+  	"\t`$negname`: {-1, code$cname},\n";
+}
+
+my $gen = 0;
+
+sub PrintClasses($@) {
+  my ($cname, @classes) = @_;
+  my @entries;
+  foreach my $cl (@classes) {
+    my @ranges = ComputeClass($cl);
+    push @entries, PrintClass(++$gen, $cl, @ranges);
+  }
+  print "var ${cname}Group = map[string]charGroup{\n";
+  foreach my $e (@entries) {
+    print $e;
+  }
+  print "}\n";
+  my $count = @entries;
+}
+
+print <<EOF;
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// GENERATED BY make_perl_groups.pl; DO NOT EDIT.
+// make_perl_groups.pl >perl_groups.go
+
+package syntax
+
+EOF
+
+PrintClasses("perl", @perlclasses);
+PrintClasses("posix", @posixclasses);
diff --git a/src/regexp/syntax/op_string.go b/src/regexp/syntax/op_string.go
new file mode 100644
index 0000000..1368f5b
--- /dev/null
+++ b/src/regexp/syntax/op_string.go
@@ -0,0 +1,52 @@
+// Code generated by "stringer -type Op -trimprefix Op"; DO NOT EDIT.
+
+package syntax
+
+import "strconv"
+
+func _() {
+	// An "invalid array index" compiler error signifies that the constant values have changed.
+	// Re-run the stringer command to generate them again.
+	var x [1]struct{}
+	_ = x[OpNoMatch-1]
+	_ = x[OpEmptyMatch-2]
+	_ = x[OpLiteral-3]
+	_ = x[OpCharClass-4]
+	_ = x[OpAnyCharNotNL-5]
+	_ = x[OpAnyChar-6]
+	_ = x[OpBeginLine-7]
+	_ = x[OpEndLine-8]
+	_ = x[OpBeginText-9]
+	_ = x[OpEndText-10]
+	_ = x[OpWordBoundary-11]
+	_ = x[OpNoWordBoundary-12]
+	_ = x[OpCapture-13]
+	_ = x[OpStar-14]
+	_ = x[OpPlus-15]
+	_ = x[OpQuest-16]
+	_ = x[OpRepeat-17]
+	_ = x[OpConcat-18]
+	_ = x[OpAlternate-19]
+	_ = x[opPseudo-128]
+}
+
+const (
+	_Op_name_0 = "NoMatchEmptyMatchLiteralCharClassAnyCharNotNLAnyCharBeginLineEndLineBeginTextEndTextWordBoundaryNoWordBoundaryCaptureStarPlusQuestRepeatConcatAlternate"
+	_Op_name_1 = "opPseudo"
+)
+
+var (
+	_Op_index_0 = [...]uint8{0, 7, 17, 24, 33, 45, 52, 61, 68, 77, 84, 96, 110, 117, 121, 125, 130, 136, 142, 151}
+)
+
+func (i Op) String() string {
+	switch {
+	case 1 <= i && i <= 19:
+		i -= 1
+		return _Op_name_0[_Op_index_0[i]:_Op_index_0[i+1]]
+	case i == 128:
+		return _Op_name_1
+	default:
+		return "Op(" + strconv.FormatInt(int64(i), 10) + ")"
+	}
+}
diff --git a/src/regexp/syntax/parse.go b/src/regexp/syntax/parse.go
new file mode 100644
index 0000000..6a11b53
--- /dev/null
+++ b/src/regexp/syntax/parse.go
@@ -0,0 +1,2138 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+import (
+	"sort"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// An Error describes a failure to parse a regular expression
+// and gives the offending expression.
+type Error struct {
+	Code ErrorCode
+	Expr string
+}
+
+func (e *Error) Error() string {
+	return "error parsing regexp: " + e.Code.String() + ": `" + e.Expr + "`"
+}
+
+// An ErrorCode describes a failure to parse a regular expression.
+type ErrorCode string
+
+const (
+	// Unexpected error
+	ErrInternalError ErrorCode = "regexp/syntax: internal error"
+
+	// Parse errors
+	ErrInvalidCharClass      ErrorCode = "invalid character class"
+	ErrInvalidCharRange      ErrorCode = "invalid character class range"
+	ErrInvalidEscape         ErrorCode = "invalid escape sequence"
+	ErrInvalidNamedCapture   ErrorCode = "invalid named capture"
+	ErrInvalidPerlOp         ErrorCode = "invalid or unsupported Perl syntax"
+	ErrInvalidRepeatOp       ErrorCode = "invalid nested repetition operator"
+	ErrInvalidRepeatSize     ErrorCode = "invalid repeat count"
+	ErrInvalidUTF8           ErrorCode = "invalid UTF-8"
+	ErrMissingBracket        ErrorCode = "missing closing ]"
+	ErrMissingParen          ErrorCode = "missing closing )"
+	ErrMissingRepeatArgument ErrorCode = "missing argument to repetition operator"
+	ErrTrailingBackslash     ErrorCode = "trailing backslash at end of expression"
+	ErrUnexpectedParen       ErrorCode = "unexpected )"
+	ErrNestingDepth          ErrorCode = "expression nests too deeply"
+	ErrLarge                 ErrorCode = "expression too large"
+)
+
+func (e ErrorCode) String() string {
+	return string(e)
+}
+
+// Flags control the behavior of the parser and record information about regexp context.
+type Flags uint16
+
+const (
+	FoldCase      Flags = 1 << iota // case-insensitive match
+	Literal                         // treat pattern as literal string
+	ClassNL                         // allow character classes like [^a-z] and [[:space:]] to match newline
+	DotNL                           // allow . to match newline
+	OneLine                         // treat ^ and $ as only matching at beginning and end of text
+	NonGreedy                       // make repetition operators default to non-greedy
+	PerlX                           // allow Perl extensions
+	UnicodeGroups                   // allow \p{Han}, \P{Han} for Unicode group and negation
+	WasDollar                       // regexp OpEndText was $, not \z
+	Simple                          // regexp contains no counted repetition
+
+	MatchNL = ClassNL | DotNL
+
+	Perl        = ClassNL | OneLine | PerlX | UnicodeGroups // as close to Perl as possible
+	POSIX Flags = 0                                         // POSIX syntax
+)
+
+// Pseudo-ops for parsing stack.
+const (
+	opLeftParen = opPseudo + iota
+	opVerticalBar
+)
+
+// maxHeight is the maximum height of a regexp parse tree.
+// It is somewhat arbitrarily chosen, but the idea is to be large enough
+// that no one will actually hit in real use but at the same time small enough
+// that recursion on the Regexp tree will not hit the 1GB Go stack limit.
+// The maximum amount of stack for a single recursive frame is probably
+// closer to 1kB, so this could potentially be raised, but it seems unlikely
+// that people have regexps nested even this deeply.
+// We ran a test on Google's C++ code base and turned up only
+// a single use case with depth > 100; it had depth 128.
+// Using depth 1000 should be plenty of margin.
+// As an optimization, we don't even bother calculating heights
+// until we've allocated at least maxHeight Regexp structures.
+const maxHeight = 1000
+
+// maxSize is the maximum size of a compiled regexp in Insts.
+// It too is somewhat arbitrarily chosen, but the idea is to be large enough
+// to allow significant regexps while at the same time small enough that
+// the compiled form will not take up too much memory.
+// 128 MB is enough for a 3.3 million Inst structures, which roughly
+// corresponds to a 3.3 MB regexp.
+const (
+	maxSize  = 128 << 20 / instSize
+	instSize = 5 * 8 // byte, 2 uint32, slice is 5 64-bit words
+)
+
+// maxRunes is the maximum number of runes allowed in a regexp tree
+// counting the runes in all the nodes.
+// Ignoring character classes p.numRunes is always less than the length of the regexp.
+// Character classes can make it much larger: each \pL adds 1292 runes.
+// 128 MB is enough for 32M runes, which is over 26k \pL instances.
+// Note that repetitions do not make copies of the rune slices,
+// so \pL{1000} is only one rune slice, not 1000.
+// We could keep a cache of character classes we've seen,
+// so that all the \pL we see use the same rune list,
+// but that doesn't remove the problem entirely:
+// consider something like [\pL01234][\pL01235][\pL01236]...[\pL^&*()].
+// And because the Rune slice is exposed directly in the Regexp,
+// there is not an opportunity to change the representation to allow
+// partial sharing between different character classes.
+// So the limit is the best we can do.
+const (
+	maxRunes = 128 << 20 / runeSize
+	runeSize = 4 // rune is int32
+)
+
+type parser struct {
+	flags       Flags     // parse mode flags
+	stack       []*Regexp // stack of parsed expressions
+	free        *Regexp
+	numCap      int // number of capturing groups seen
+	wholeRegexp string
+	tmpClass    []rune            // temporary char class work space
+	numRegexp   int               // number of regexps allocated
+	numRunes    int               // number of runes in char classes
+	repeats     int64             // product of all repetitions seen
+	height      map[*Regexp]int   // regexp height, for height limit check
+	size        map[*Regexp]int64 // regexp compiled size, for size limit check
+}
+
+func (p *parser) newRegexp(op Op) *Regexp {
+	re := p.free
+	if re != nil {
+		p.free = re.Sub0[0]
+		*re = Regexp{}
+	} else {
+		re = new(Regexp)
+		p.numRegexp++
+	}
+	re.Op = op
+	return re
+}
+
+func (p *parser) reuse(re *Regexp) {
+	if p.height != nil {
+		delete(p.height, re)
+	}
+	re.Sub0[0] = p.free
+	p.free = re
+}
+
+func (p *parser) checkLimits(re *Regexp) {
+	if p.numRunes > maxRunes {
+		panic(ErrLarge)
+	}
+	p.checkSize(re)
+	p.checkHeight(re)
+}
+
+func (p *parser) checkSize(re *Regexp) {
+	if p.size == nil {
+		// We haven't started tracking size yet.
+		// Do a relatively cheap check to see if we need to start.
+		// Maintain the product of all the repeats we've seen
+		// and don't track if the total number of regexp nodes
+		// we've seen times the repeat product is in budget.
+		if p.repeats == 0 {
+			p.repeats = 1
+		}
+		if re.Op == OpRepeat {
+			n := re.Max
+			if n == -1 {
+				n = re.Min
+			}
+			if n <= 0 {
+				n = 1
+			}
+			if int64(n) > maxSize/p.repeats {
+				p.repeats = maxSize
+			} else {
+				p.repeats *= int64(n)
+			}
+		}
+		if int64(p.numRegexp) < maxSize/p.repeats {
+			return
+		}
+
+		// We need to start tracking size.
+		// Make the map and belatedly populate it
+		// with info about everything we've constructed so far.
+		p.size = make(map[*Regexp]int64)
+		for _, re := range p.stack {
+			p.checkSize(re)
+		}
+	}
+
+	if p.calcSize(re, true) > maxSize {
+		panic(ErrLarge)
+	}
+}
+
+func (p *parser) calcSize(re *Regexp, force bool) int64 {
+	if !force {
+		if size, ok := p.size[re]; ok {
+			return size
+		}
+	}
+
+	var size int64
+	switch re.Op {
+	case OpLiteral:
+		size = int64(len(re.Rune))
+	case OpCapture, OpStar:
+		// star can be 1+ or 2+; assume 2 pessimistically
+		size = 2 + p.calcSize(re.Sub[0], false)
+	case OpPlus, OpQuest:
+		size = 1 + p.calcSize(re.Sub[0], false)
+	case OpConcat:
+		for _, sub := range re.Sub {
+			size += p.calcSize(sub, false)
+		}
+	case OpAlternate:
+		for _, sub := range re.Sub {
+			size += p.calcSize(sub, false)
+		}
+		if len(re.Sub) > 1 {
+			size += int64(len(re.Sub)) - 1
+		}
+	case OpRepeat:
+		sub := p.calcSize(re.Sub[0], false)
+		if re.Max == -1 {
+			if re.Min == 0 {
+				size = 2 + sub // x*
+			} else {
+				size = 1 + int64(re.Min)*sub // xxx+
+			}
+			break
+		}
+		// x{2,5} = xx(x(x(x)?)?)?
+		size = int64(re.Max)*sub + int64(re.Max-re.Min)
+	}
+
+	if size < 1 {
+		size = 1
+	}
+	p.size[re] = size
+	return size
+}
+
+func (p *parser) checkHeight(re *Regexp) {
+	if p.numRegexp < maxHeight {
+		return
+	}
+	if p.height == nil {
+		p.height = make(map[*Regexp]int)
+		for _, re := range p.stack {
+			p.checkHeight(re)
+		}
+	}
+	if p.calcHeight(re, true) > maxHeight {
+		panic(ErrNestingDepth)
+	}
+}
+
+func (p *parser) calcHeight(re *Regexp, force bool) int {
+	if !force {
+		if h, ok := p.height[re]; ok {
+			return h
+		}
+	}
+	h := 1
+	for _, sub := range re.Sub {
+		hsub := p.calcHeight(sub, false)
+		if h < 1+hsub {
+			h = 1 + hsub
+		}
+	}
+	p.height[re] = h
+	return h
+}
+
+// Parse stack manipulation.
+
+// push pushes the regexp re onto the parse stack and returns the regexp.
+func (p *parser) push(re *Regexp) *Regexp {
+	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] &&
+		unicode.SimpleFold(re.Rune[0]) == re.Rune[2] &&
+		unicode.SimpleFold(re.Rune[2]) == re.Rune[0] ||
+		re.Op == OpCharClass && len(re.Rune) == 2 &&
+			re.Rune[0]+1 == re.Rune[1] &&
+			unicode.SimpleFold(re.Rune[0]) == re.Rune[1] &&
+			unicode.SimpleFold(re.Rune[1]) == re.Rune[0] {
+		// Case-insensitive rune like [Aa] or [Δδ].
+		if p.maybeConcat(re.Rune[0], p.flags|FoldCase) {
+			return nil
+		}
+
+		// Rewrite as (case-insensitive) literal.
+		re.Op = OpLiteral
+		re.Rune = re.Rune[:1]
+		re.Flags = p.flags | FoldCase
+	} else {
+		// Incremental concatenation.
+		p.maybeConcat(-1, 0)
+	}
+
+	p.stack = append(p.stack, re)
+	p.checkLimits(re)
+	return re
+}
+
+// maybeConcat implements incremental concatenation
+// of literal runes into string nodes. The parser calls this
+// before each push, so only the top fragment of the stack
+// might need processing. Since this is called before a push,
+// the topmost literal is no longer subject to operators like *
+// (Otherwise ab* would turn into (ab)*.)
+// If r >= 0 and there's a node left over, maybeConcat uses it
+// to push r with the given flags.
+// maybeConcat reports whether r was pushed.
+func (p *parser) maybeConcat(r rune, flags Flags) bool {
+	n := len(p.stack)
+	if n < 2 {
+		return false
+	}
+
+	re1 := p.stack[n-1]
+	re2 := p.stack[n-2]
+	if re1.Op != OpLiteral || re2.Op != OpLiteral || re1.Flags&FoldCase != re2.Flags&FoldCase {
+		return false
+	}
+
+	// Push re1 into re2.
+	re2.Rune = append(re2.Rune, re1.Rune...)
+
+	// Reuse re1 if possible.
+	if r >= 0 {
+		re1.Rune = re1.Rune0[:1]
+		re1.Rune[0] = r
+		re1.Flags = flags
+		return true
+	}
+
+	p.stack = p.stack[:n-1]
+	p.reuse(re1)
+	return false // did not push r
+}
+
+// literal pushes a literal regexp for the rune r on the stack.
+func (p *parser) literal(r rune) {
+	re := p.newRegexp(OpLiteral)
+	re.Flags = p.flags
+	if p.flags&FoldCase != 0 {
+		r = minFoldRune(r)
+	}
+	re.Rune0[0] = r
+	re.Rune = re.Rune0[:1]
+	p.push(re)
+}
+
+// minFoldRune returns the minimum rune fold-equivalent to r.
+func minFoldRune(r rune) rune {
+	if r < minFold || r > maxFold {
+		return r
+	}
+	m := r
+	r0 := r
+	for r = unicode.SimpleFold(r); r != r0; r = unicode.SimpleFold(r) {
+		m = min(m, r)
+	}
+	return m
+}
+
+// op pushes a regexp with the given op onto the stack
+// and returns that regexp.
+func (p *parser) op(op Op) *Regexp {
+	re := p.newRegexp(op)
+	re.Flags = p.flags
+	return p.push(re)
+}
+
+// repeat replaces the top stack element with itself repeated according to op, min, max.
+// before is the regexp suffix starting at the repetition operator.
+// after is the regexp suffix following after the repetition operator.
+// repeat returns an updated 'after' and an error, if any.
+func (p *parser) repeat(op Op, min, max int, before, after, lastRepeat string) (string, error) {
+	flags := p.flags
+	if p.flags&PerlX != 0 {
+		if len(after) > 0 && after[0] == '?' {
+			after = after[1:]
+			flags ^= NonGreedy
+		}
+		if lastRepeat != "" {
+			// In Perl it is not allowed to stack repetition operators:
+			// a** is a syntax error, not a doubled star, and a++ means
+			// something else entirely, which we don't support!
+			return "", &Error{ErrInvalidRepeatOp, lastRepeat[:len(lastRepeat)-len(after)]}
+		}
+	}
+	n := len(p.stack)
+	if n == 0 {
+		return "", &Error{ErrMissingRepeatArgument, before[:len(before)-len(after)]}
+	}
+	sub := p.stack[n-1]
+	if sub.Op >= opPseudo {
+		return "", &Error{ErrMissingRepeatArgument, before[:len(before)-len(after)]}
+	}
+
+	re := p.newRegexp(op)
+	re.Min = min
+	re.Max = max
+	re.Flags = flags
+	re.Sub = re.Sub0[:1]
+	re.Sub[0] = sub
+	p.stack[n-1] = re
+	p.checkLimits(re)
+
+	if op == OpRepeat && (min >= 2 || max >= 2) && !repeatIsValid(re, 1000) {
+		return "", &Error{ErrInvalidRepeatSize, before[:len(before)-len(after)]}
+	}
+
+	return after, nil
+}
+
+// repeatIsValid reports whether the repetition re is valid.
+// Valid means that the combination of the top-level repetition
+// and any inner repetitions does not exceed n copies of the
+// innermost thing.
+// This function rewalks the regexp tree and is called for every repetition,
+// so we have to worry about inducing quadratic behavior in the parser.
+// We avoid this by only calling repeatIsValid when min or max >= 2.
+// In that case the depth of any >= 2 nesting can only get to 9 without
+// triggering a parse error, so each subtree can only be rewalked 9 times.
+func repeatIsValid(re *Regexp, n int) bool {
+	if re.Op == OpRepeat {
+		m := re.Max
+		if m == 0 {
+			return true
+		}
+		if m < 0 {
+			m = re.Min
+		}
+		if m > n {
+			return false
+		}
+		if m > 0 {
+			n /= m
+		}
+	}
+	for _, sub := range re.Sub {
+		if !repeatIsValid(sub, n) {
+			return false
+		}
+	}
+	return true
+}
+
+// concat replaces the top of the stack (above the topmost '|' or '(') with its concatenation.
+func (p *parser) concat() *Regexp {
+	p.maybeConcat(-1, 0)
+
+	// Scan down to find pseudo-operator | or (.
+	i := len(p.stack)
+	for i > 0 && p.stack[i-1].Op < opPseudo {
+		i--
+	}
+	subs := p.stack[i:]
+	p.stack = p.stack[:i]
+
+	// Empty concatenation is special case.
+	if len(subs) == 0 {
+		return p.push(p.newRegexp(OpEmptyMatch))
+	}
+
+	return p.push(p.collapse(subs, OpConcat))
+}
+
+// alternate replaces the top of the stack (above the topmost '(') with its alternation.
+func (p *parser) alternate() *Regexp {
+	// Scan down to find pseudo-operator (.
+	// There are no | above (.
+	i := len(p.stack)
+	for i > 0 && p.stack[i-1].Op < opPseudo {
+		i--
+	}
+	subs := p.stack[i:]
+	p.stack = p.stack[:i]
+
+	// Make sure top class is clean.
+	// All the others already are (see swapVerticalBar).
+	if len(subs) > 0 {
+		cleanAlt(subs[len(subs)-1])
+	}
+
+	// Empty alternate is special case
+	// (shouldn't happen but easy to handle).
+	if len(subs) == 0 {
+		return p.push(p.newRegexp(OpNoMatch))
+	}
+
+	return p.push(p.collapse(subs, OpAlternate))
+}
+
+// cleanAlt cleans re for eventual inclusion in an alternation.
+func cleanAlt(re *Regexp) {
+	switch re.Op {
+	case OpCharClass:
+		re.Rune = cleanClass(&re.Rune)
+		if len(re.Rune) == 2 && re.Rune[0] == 0 && re.Rune[1] == unicode.MaxRune {
+			re.Rune = nil
+			re.Op = OpAnyChar
+			return
+		}
+		if len(re.Rune) == 4 && re.Rune[0] == 0 && re.Rune[1] == '\n'-1 && re.Rune[2] == '\n'+1 && re.Rune[3] == unicode.MaxRune {
+			re.Rune = nil
+			re.Op = OpAnyCharNotNL
+			return
+		}
+		if cap(re.Rune)-len(re.Rune) > 100 {
+			// re.Rune will not grow any more.
+			// Make a copy or inline to reclaim storage.
+			re.Rune = append(re.Rune0[:0], re.Rune...)
+		}
+	}
+}
+
+// collapse returns the result of applying op to sub.
+// If sub contains op nodes, they all get hoisted up
+// so that there is never a concat of a concat or an
+// alternate of an alternate.
+func (p *parser) collapse(subs []*Regexp, op Op) *Regexp {
+	if len(subs) == 1 {
+		return subs[0]
+	}
+	re := p.newRegexp(op)
+	re.Sub = re.Sub0[:0]
+	for _, sub := range subs {
+		if sub.Op == op {
+			re.Sub = append(re.Sub, sub.Sub...)
+			p.reuse(sub)
+		} else {
+			re.Sub = append(re.Sub, sub)
+		}
+	}
+	if op == OpAlternate {
+		re.Sub = p.factor(re.Sub)
+		if len(re.Sub) == 1 {
+			old := re
+			re = re.Sub[0]
+			p.reuse(old)
+		}
+	}
+	return re
+}
+
+// factor factors common prefixes from the alternation list sub.
+// It returns a replacement list that reuses the same storage and
+// frees (passes to p.reuse) any removed *Regexps.
+//
+// For example,
+//
+//	ABC|ABD|AEF|BCX|BCY
+//
+// simplifies by literal prefix extraction to
+//
+//	A(B(C|D)|EF)|BC(X|Y)
+//
+// which simplifies by character class introduction to
+//
+//	A(B[CD]|EF)|BC[XY]
+func (p *parser) factor(sub []*Regexp) []*Regexp {
+	if len(sub) < 2 {
+		return sub
+	}
+
+	// Round 1: Factor out common literal prefixes.
+	var str []rune
+	var strflags Flags
+	start := 0
+	out := sub[:0]
+	for i := 0; i <= len(sub); i++ {
+		// Invariant: the Regexps that were in sub[0:start] have been
+		// used or marked for reuse, and the slice space has been reused
+		// for out (len(out) <= start).
+		//
+		// Invariant: sub[start:i] consists of regexps that all begin
+		// with str as modified by strflags.
+		var istr []rune
+		var iflags Flags
+		if i < len(sub) {
+			istr, iflags = p.leadingString(sub[i])
+			if iflags == strflags {
+				same := 0
+				for same < len(str) && same < len(istr) && str[same] == istr[same] {
+					same++
+				}
+				if same > 0 {
+					// Matches at least one rune in current range.
+					// Keep going around.
+					str = str[:same]
+					continue
+				}
+			}
+		}
+
+		// Found end of a run with common leading literal string:
+		// sub[start:i] all begin with str[0:len(str)], but sub[i]
+		// does not even begin with str[0].
+		//
+		// Factor out common string and append factored expression to out.
+		if i == start {
+			// Nothing to do - run of length 0.
+		} else if i == start+1 {
+			// Just one: don't bother factoring.
+			out = append(out, sub[start])
+		} else {
+			// Construct factored form: prefix(suffix1|suffix2|...)
+			prefix := p.newRegexp(OpLiteral)
+			prefix.Flags = strflags
+			prefix.Rune = append(prefix.Rune[:0], str...)
+
+			for j := start; j < i; j++ {
+				sub[j] = p.removeLeadingString(sub[j], len(str))
+				p.checkLimits(sub[j])
+			}
+			suffix := p.collapse(sub[start:i], OpAlternate) // recurse
+
+			re := p.newRegexp(OpConcat)
+			re.Sub = append(re.Sub[:0], prefix, suffix)
+			out = append(out, re)
+		}
+
+		// Prepare for next iteration.
+		start = i
+		str = istr
+		strflags = iflags
+	}
+	sub = out
+
+	// Round 2: Factor out common simple prefixes,
+	// just the first piece of each concatenation.
+	// This will be good enough a lot of the time.
+	//
+	// Complex subexpressions (e.g. involving quantifiers)
+	// are not safe to factor because that collapses their
+	// distinct paths through the automaton, which affects
+	// correctness in some cases.
+	start = 0
+	out = sub[:0]
+	var first *Regexp
+	for i := 0; i <= len(sub); i++ {
+		// Invariant: the Regexps that were in sub[0:start] have been
+		// used or marked for reuse, and the slice space has been reused
+		// for out (len(out) <= start).
+		//
+		// Invariant: sub[start:i] consists of regexps that all begin with ifirst.
+		var ifirst *Regexp
+		if i < len(sub) {
+			ifirst = p.leadingRegexp(sub[i])
+			if first != nil && first.Equal(ifirst) &&
+				// first must be a character class OR a fixed repeat of a character class.
+				(isCharClass(first) || (first.Op == OpRepeat && first.Min == first.Max && isCharClass(first.Sub[0]))) {
+				continue
+			}
+		}
+
+		// Found end of a run with common leading regexp:
+		// sub[start:i] all begin with first but sub[i] does not.
+		//
+		// Factor out common regexp and append factored expression to out.
+		if i == start {
+			// Nothing to do - run of length 0.
+		} else if i == start+1 {
+			// Just one: don't bother factoring.
+			out = append(out, sub[start])
+		} else {
+			// Construct factored form: prefix(suffix1|suffix2|...)
+			prefix := first
+			for j := start; j < i; j++ {
+				reuse := j != start // prefix came from sub[start]
+				sub[j] = p.removeLeadingRegexp(sub[j], reuse)
+				p.checkLimits(sub[j])
+			}
+			suffix := p.collapse(sub[start:i], OpAlternate) // recurse
+
+			re := p.newRegexp(OpConcat)
+			re.Sub = append(re.Sub[:0], prefix, suffix)
+			out = append(out, re)
+		}
+
+		// Prepare for next iteration.
+		start = i
+		first = ifirst
+	}
+	sub = out
+
+	// Round 3: Collapse runs of single literals into character classes.
+	start = 0
+	out = sub[:0]
+	for i := 0; i <= len(sub); i++ {
+		// Invariant: the Regexps that were in sub[0:start] have been
+		// used or marked for reuse, and the slice space has been reused
+		// for out (len(out) <= start).
+		//
+		// Invariant: sub[start:i] consists of regexps that are either
+		// literal runes or character classes.
+		if i < len(sub) && isCharClass(sub[i]) {
+			continue
+		}
+
+		// sub[i] is not a char or char class;
+		// emit char class for sub[start:i]...
+		if i == start {
+			// Nothing to do - run of length 0.
+		} else if i == start+1 {
+			out = append(out, sub[start])
+		} else {
+			// Make new char class.
+			// Start with most complex regexp in sub[start].
+			max := start
+			for j := start + 1; j < i; j++ {
+				if sub[max].Op < sub[j].Op || sub[max].Op == sub[j].Op && len(sub[max].Rune) < len(sub[j].Rune) {
+					max = j
+				}
+			}
+			sub[start], sub[max] = sub[max], sub[start]
+
+			for j := start + 1; j < i; j++ {
+				mergeCharClass(sub[start], sub[j])
+				p.reuse(sub[j])
+			}
+			cleanAlt(sub[start])
+			out = append(out, sub[start])
+		}
+
+		// ... and then emit sub[i].
+		if i < len(sub) {
+			out = append(out, sub[i])
+		}
+		start = i + 1
+	}
+	sub = out
+
+	// Round 4: Collapse runs of empty matches into a single empty match.
+	start = 0
+	out = sub[:0]
+	for i := range sub {
+		if i+1 < len(sub) && sub[i].Op == OpEmptyMatch && sub[i+1].Op == OpEmptyMatch {
+			continue
+		}
+		out = append(out, sub[i])
+	}
+	sub = out
+
+	return sub
+}
+
+// leadingString returns the leading literal string that re begins with.
+// The string refers to storage in re or its children.
+func (p *parser) leadingString(re *Regexp) ([]rune, Flags) {
+	if re.Op == OpConcat && len(re.Sub) > 0 {
+		re = re.Sub[0]
+	}
+	if re.Op != OpLiteral {
+		return nil, 0
+	}
+	return re.Rune, re.Flags & FoldCase
+}
+
+// removeLeadingString removes the first n leading runes
+// from the beginning of re. It returns the replacement for re.
+func (p *parser) removeLeadingString(re *Regexp, n int) *Regexp {
+	if re.Op == OpConcat && len(re.Sub) > 0 {
+		// Removing a leading string in a concatenation
+		// might simplify the concatenation.
+		sub := re.Sub[0]
+		sub = p.removeLeadingString(sub, n)
+		re.Sub[0] = sub
+		if sub.Op == OpEmptyMatch {
+			p.reuse(sub)
+			switch len(re.Sub) {
+			case 0, 1:
+				// Impossible but handle.
+				re.Op = OpEmptyMatch
+				re.Sub = nil
+			case 2:
+				old := re
+				re = re.Sub[1]
+				p.reuse(old)
+			default:
+				copy(re.Sub, re.Sub[1:])
+				re.Sub = re.Sub[:len(re.Sub)-1]
+			}
+		}
+		return re
+	}
+
+	if re.Op == OpLiteral {
+		re.Rune = re.Rune[:copy(re.Rune, re.Rune[n:])]
+		if len(re.Rune) == 0 {
+			re.Op = OpEmptyMatch
+		}
+	}
+	return re
+}
+
+// leadingRegexp returns the leading regexp that re begins with.
+// The regexp refers to storage in re or its children.
+func (p *parser) leadingRegexp(re *Regexp) *Regexp {
+	if re.Op == OpEmptyMatch {
+		return nil
+	}
+	if re.Op == OpConcat && len(re.Sub) > 0 {
+		sub := re.Sub[0]
+		if sub.Op == OpEmptyMatch {
+			return nil
+		}
+		return sub
+	}
+	return re
+}
+
+// removeLeadingRegexp removes the leading regexp in re.
+// It returns the replacement for re.
+// If reuse is true, it passes the removed regexp (if no longer needed) to p.reuse.
+func (p *parser) removeLeadingRegexp(re *Regexp, reuse bool) *Regexp {
+	if re.Op == OpConcat && len(re.Sub) > 0 {
+		if reuse {
+			p.reuse(re.Sub[0])
+		}
+		re.Sub = re.Sub[:copy(re.Sub, re.Sub[1:])]
+		switch len(re.Sub) {
+		case 0:
+			re.Op = OpEmptyMatch
+			re.Sub = nil
+		case 1:
+			old := re
+			re = re.Sub[0]
+			p.reuse(old)
+		}
+		return re
+	}
+	if reuse {
+		p.reuse(re)
+	}
+	return p.newRegexp(OpEmptyMatch)
+}
+
+func literalRegexp(s string, flags Flags) *Regexp {
+	re := &Regexp{Op: OpLiteral}
+	re.Flags = flags
+	re.Rune = re.Rune0[:0] // use local storage for small strings
+	for _, c := range s {
+		if len(re.Rune) >= cap(re.Rune) {
+			// string is too long to fit in Rune0.  let Go handle it
+			re.Rune = []rune(s)
+			break
+		}
+		re.Rune = append(re.Rune, c)
+	}
+	return re
+}
+
+// Parsing.
+
+// Parse parses a regular expression string s, controlled by the specified
+// Flags, and returns a regular expression parse tree. The syntax is
+// described in the top-level comment.
+func Parse(s string, flags Flags) (*Regexp, error) {
+	return parse(s, flags)
+}
+
+func parse(s string, flags Flags) (_ *Regexp, err error) {
+	defer func() {
+		switch r := recover(); r {
+		default:
+			panic(r)
+		case nil:
+			// ok
+		case ErrLarge: // too big
+			err = &Error{Code: ErrLarge, Expr: s}
+		case ErrNestingDepth:
+			err = &Error{Code: ErrNestingDepth, Expr: s}
+		}
+	}()
+
+	if flags&Literal != 0 {
+		// Trivial parser for literal string.
+		if err := checkUTF8(s); err != nil {
+			return nil, err
+		}
+		return literalRegexp(s, flags), nil
+	}
+
+	// Otherwise, must do real work.
+	var (
+		p          parser
+		c          rune
+		op         Op
+		lastRepeat string
+	)
+	p.flags = flags
+	p.wholeRegexp = s
+	t := s
+	for t != "" {
+		repeat := ""
+	BigSwitch:
+		switch t[0] {
+		default:
+			if c, t, err = nextRune(t); err != nil {
+				return nil, err
+			}
+			p.literal(c)
+
+		case '(':
+			if p.flags&PerlX != 0 && len(t) >= 2 && t[1] == '?' {
+				// Flag changes and non-capturing groups.
+				if t, err = p.parsePerlFlags(t); err != nil {
+					return nil, err
+				}
+				break
+			}
+			p.numCap++
+			p.op(opLeftParen).Cap = p.numCap
+			t = t[1:]
+		case '|':
+			if err = p.parseVerticalBar(); err != nil {
+				return nil, err
+			}
+			t = t[1:]
+		case ')':
+			if err = p.parseRightParen(); err != nil {
+				return nil, err
+			}
+			t = t[1:]
+		case '^':
+			if p.flags&OneLine != 0 {
+				p.op(OpBeginText)
+			} else {
+				p.op(OpBeginLine)
+			}
+			t = t[1:]
+		case '$':
+			if p.flags&OneLine != 0 {
+				p.op(OpEndText).Flags |= WasDollar
+			} else {
+				p.op(OpEndLine)
+			}
+			t = t[1:]
+		case '.':
+			if p.flags&DotNL != 0 {
+				p.op(OpAnyChar)
+			} else {
+				p.op(OpAnyCharNotNL)
+			}
+			t = t[1:]
+		case '[':
+			if t, err = p.parseClass(t); err != nil {
+				return nil, err
+			}
+		case '*', '+', '?':
+			before := t
+			switch t[0] {
+			case '*':
+				op = OpStar
+			case '+':
+				op = OpPlus
+			case '?':
+				op = OpQuest
+			}
+			after := t[1:]
+			if after, err = p.repeat(op, 0, 0, before, after, lastRepeat); err != nil {
+				return nil, err
+			}
+			repeat = before
+			t = after
+		case '{':
+			op = OpRepeat
+			before := t
+			min, max, after, ok := p.parseRepeat(t)
+			if !ok {
+				// If the repeat cannot be parsed, { is a literal.
+				p.literal('{')
+				t = t[1:]
+				break
+			}
+			if min < 0 || min > 1000 || max > 1000 || max >= 0 && min > max {
+				// Numbers were too big, or max is present and min > max.
+				return nil, &Error{ErrInvalidRepeatSize, before[:len(before)-len(after)]}
+			}
+			if after, err = p.repeat(op, min, max, before, after, lastRepeat); err != nil {
+				return nil, err
+			}
+			repeat = before
+			t = after
+		case '\\':
+			if p.flags&PerlX != 0 && len(t) >= 2 {
+				switch t[1] {
+				case 'A':
+					p.op(OpBeginText)
+					t = t[2:]
+					break BigSwitch
+				case 'b':
+					p.op(OpWordBoundary)
+					t = t[2:]
+					break BigSwitch
+				case 'B':
+					p.op(OpNoWordBoundary)
+					t = t[2:]
+					break BigSwitch
+				case 'C':
+					// any byte; not supported
+					return nil, &Error{ErrInvalidEscape, t[:2]}
+				case 'Q':
+					// \Q ... \E: the ... is always literals
+					var lit string
+					lit, t, _ = strings.Cut(t[2:], `\E`)
+					for lit != "" {
+						c, rest, err := nextRune(lit)
+						if err != nil {
+							return nil, err
+						}
+						p.literal(c)
+						lit = rest
+					}
+					break BigSwitch
+				case 'z':
+					p.op(OpEndText)
+					t = t[2:]
+					break BigSwitch
+				}
+			}
+
+			re := p.newRegexp(OpCharClass)
+			re.Flags = p.flags
+
+			// Look for Unicode character group like \p{Han}
+			if len(t) >= 2 && (t[1] == 'p' || t[1] == 'P') {
+				r, rest, err := p.parseUnicodeClass(t, re.Rune0[:0])
+				if err != nil {
+					return nil, err
+				}
+				if r != nil {
+					re.Rune = r
+					t = rest
+					p.push(re)
+					break BigSwitch
+				}
+			}
+
+			// Perl character class escape.
+			if r, rest := p.parsePerlClassEscape(t, re.Rune0[:0]); r != nil {
+				re.Rune = r
+				t = rest
+				p.push(re)
+				break BigSwitch
+			}
+			p.reuse(re)
+
+			// Ordinary single-character escape.
+			if c, t, err = p.parseEscape(t); err != nil {
+				return nil, err
+			}
+			p.literal(c)
+		}
+		lastRepeat = repeat
+	}
+
+	p.concat()
+	if p.swapVerticalBar() {
+		// pop vertical bar
+		p.stack = p.stack[:len(p.stack)-1]
+	}
+	p.alternate()
+
+	n := len(p.stack)
+	if n != 1 {
+		return nil, &Error{ErrMissingParen, s}
+	}
+	return p.stack[0], nil
+}
+
+// parseRepeat parses {min} (max=min) or {min,} (max=-1) or {min,max}.
+// If s is not of that form, it returns ok == false.
+// If s has the right form but the values are too big, it returns min == -1, ok == true.
+func (p *parser) parseRepeat(s string) (min, max int, rest string, ok bool) {
+	if s == "" || s[0] != '{' {
+		return
+	}
+	s = s[1:]
+	var ok1 bool
+	if min, s, ok1 = p.parseInt(s); !ok1 {
+		return
+	}
+	if s == "" {
+		return
+	}
+	if s[0] != ',' {
+		max = min
+	} else {
+		s = s[1:]
+		if s == "" {
+			return
+		}
+		if s[0] == '}' {
+			max = -1
+		} else if max, s, ok1 = p.parseInt(s); !ok1 {
+			return
+		} else if max < 0 {
+			// parseInt found too big a number
+			min = -1
+		}
+	}
+	if s == "" || s[0] != '}' {
+		return
+	}
+	rest = s[1:]
+	ok = true
+	return
+}
+
+// parsePerlFlags parses a Perl flag setting or non-capturing group or both,
+// like (?i) or (?: or (?i:.  It removes the prefix from s and updates the parse state.
+// The caller must have ensured that s begins with "(?".
+func (p *parser) parsePerlFlags(s string) (rest string, err error) {
+	t := s
+
+	// Check for named captures, first introduced in Python's regexp library.
+	// As usual, there are three slightly different syntaxes:
+	//
+	//   (?P<name>expr)   the original, introduced by Python
+	//   (?<name>expr)    the .NET alteration, adopted by Perl 5.10
+	//   (?'name'expr)    another .NET alteration, adopted by Perl 5.10
+	//
+	// Perl 5.10 gave in and implemented the Python version too,
+	// but they claim that the last two are the preferred forms.
+	// PCRE and languages based on it (specifically, PHP and Ruby)
+	// support all three as well. EcmaScript 4 uses only the Python form.
+	//
+	// In both the open source world (via Code Search) and the
+	// Google source tree, (?P<expr>name) and (?<expr>name) are the
+	// dominant forms of named captures and both are supported.
+	startsWithP := len(t) > 4 && t[2] == 'P' && t[3] == '<'
+	startsWithName := len(t) > 3 && t[2] == '<'
+
+	if startsWithP || startsWithName {
+		// position of expr start
+		exprStartPos := 4
+		if startsWithName {
+			exprStartPos = 3
+		}
+
+		// Pull out name.
+		end := strings.IndexRune(t, '>')
+		if end < 0 {
+			if err = checkUTF8(t); err != nil {
+				return "", err
+			}
+			return "", &Error{ErrInvalidNamedCapture, s}
+		}
+
+		capture := t[:end+1]        // "(?P<name>" or "(?<name>"
+		name := t[exprStartPos:end] // "name"
+		if err = checkUTF8(name); err != nil {
+			return "", err
+		}
+		if !isValidCaptureName(name) {
+			return "", &Error{ErrInvalidNamedCapture, capture}
+		}
+
+		// Like ordinary capture, but named.
+		p.numCap++
+		re := p.op(opLeftParen)
+		re.Cap = p.numCap
+		re.Name = name
+		return t[end+1:], nil
+	}
+
+	// Non-capturing group. Might also twiddle Perl flags.
+	var c rune
+	t = t[2:] // skip (?
+	flags := p.flags
+	sign := +1
+	sawFlag := false
+Loop:
+	for t != "" {
+		if c, t, err = nextRune(t); err != nil {
+			return "", err
+		}
+		switch c {
+		default:
+			break Loop
+
+		// Flags.
+		case 'i':
+			flags |= FoldCase
+			sawFlag = true
+		case 'm':
+			flags &^= OneLine
+			sawFlag = true
+		case 's':
+			flags |= DotNL
+			sawFlag = true
+		case 'U':
+			flags |= NonGreedy
+			sawFlag = true
+
+		// Switch to negation.
+		case '-':
+			if sign < 0 {
+				break Loop
+			}
+			sign = -1
+			// Invert flags so that | above turn into &^ and vice versa.
+			// We'll invert flags again before using it below.
+			flags = ^flags
+			sawFlag = false
+
+		// End of flags, starting group or not.
+		case ':', ')':
+			if sign < 0 {
+				if !sawFlag {
+					break Loop
+				}
+				flags = ^flags
+			}
+			if c == ':' {
+				// Open new group
+				p.op(opLeftParen)
+			}
+			p.flags = flags
+			return t, nil
+		}
+	}
+
+	return "", &Error{ErrInvalidPerlOp, s[:len(s)-len(t)]}
+}
+
+// isValidCaptureName reports whether name
+// is a valid capture name: [A-Za-z0-9_]+.
+// PCRE limits names to 32 bytes.
+// Python rejects names starting with digits.
+// We don't enforce either of those.
+func isValidCaptureName(name string) bool {
+	if name == "" {
+		return false
+	}
+	for _, c := range name {
+		if c != '_' && !isalnum(c) {
+			return false
+		}
+	}
+	return true
+}
+
+// parseInt parses a decimal integer.
+func (p *parser) parseInt(s string) (n int, rest string, ok bool) {
+	if s == "" || s[0] < '0' || '9' < s[0] {
+		return
+	}
+	// Disallow leading zeros.
+	if len(s) >= 2 && s[0] == '0' && '0' <= s[1] && s[1] <= '9' {
+		return
+	}
+	t := s
+	for s != "" && '0' <= s[0] && s[0] <= '9' {
+		s = s[1:]
+	}
+	rest = s
+	ok = true
+	// Have digits, compute value.
+	t = t[:len(t)-len(s)]
+	for i := 0; i < len(t); i++ {
+		// Avoid overflow.
+		if n >= 1e8 {
+			n = -1
+			break
+		}
+		n = n*10 + int(t[i]) - '0'
+	}
+	return
+}
+
+// can this be represented as a character class?
+// single-rune literal string, char class, ., and .|\n.
+func isCharClass(re *Regexp) bool {
+	return re.Op == OpLiteral && len(re.Rune) == 1 ||
+		re.Op == OpCharClass ||
+		re.Op == OpAnyCharNotNL ||
+		re.Op == OpAnyChar
+}
+
+// does re match r?
+func matchRune(re *Regexp, r rune) bool {
+	switch re.Op {
+	case OpLiteral:
+		return len(re.Rune) == 1 && re.Rune[0] == r
+	case OpCharClass:
+		for i := 0; i < len(re.Rune); i += 2 {
+			if re.Rune[i] <= r && r <= re.Rune[i+1] {
+				return true
+			}
+		}
+		return false
+	case OpAnyCharNotNL:
+		return r != '\n'
+	case OpAnyChar:
+		return true
+	}
+	return false
+}
+
+// parseVerticalBar handles a | in the input.
+func (p *parser) parseVerticalBar() error {
+	p.concat()
+
+	// The concatenation we just parsed is on top of the stack.
+	// If it sits above an opVerticalBar, swap it below
+	// (things below an opVerticalBar become an alternation).
+	// Otherwise, push a new vertical bar.
+	if !p.swapVerticalBar() {
+		p.op(opVerticalBar)
+	}
+
+	return nil
+}
+
+// mergeCharClass makes dst = dst|src.
+// The caller must ensure that dst.Op >= src.Op,
+// to reduce the amount of copying.
+func mergeCharClass(dst, src *Regexp) {
+	switch dst.Op {
+	case OpAnyChar:
+		// src doesn't add anything.
+	case OpAnyCharNotNL:
+		// src might add \n
+		if matchRune(src, '\n') {
+			dst.Op = OpAnyChar
+		}
+	case OpCharClass:
+		// src is simpler, so either literal or char class
+		if src.Op == OpLiteral {
+			dst.Rune = appendLiteral(dst.Rune, src.Rune[0], src.Flags)
+		} else {
+			dst.Rune = appendClass(dst.Rune, src.Rune)
+		}
+	case OpLiteral:
+		// both literal
+		if src.Rune[0] == dst.Rune[0] && src.Flags == dst.Flags {
+			break
+		}
+		dst.Op = OpCharClass
+		dst.Rune = appendLiteral(dst.Rune[:0], dst.Rune[0], dst.Flags)
+		dst.Rune = appendLiteral(dst.Rune, src.Rune[0], src.Flags)
+	}
+}
+
+// If the top of the stack is an element followed by an opVerticalBar
+// swapVerticalBar swaps the two and returns true.
+// Otherwise it returns false.
+func (p *parser) swapVerticalBar() bool {
+	// If above and below vertical bar are literal or char class,
+	// can merge into a single char class.
+	n := len(p.stack)
+	if n >= 3 && p.stack[n-2].Op == opVerticalBar && isCharClass(p.stack[n-1]) && isCharClass(p.stack[n-3]) {
+		re1 := p.stack[n-1]
+		re3 := p.stack[n-3]
+		// Make re3 the more complex of the two.
+		if re1.Op > re3.Op {
+			re1, re3 = re3, re1
+			p.stack[n-3] = re3
+		}
+		mergeCharClass(re3, re1)
+		p.reuse(re1)
+		p.stack = p.stack[:n-1]
+		return true
+	}
+
+	if n >= 2 {
+		re1 := p.stack[n-1]
+		re2 := p.stack[n-2]
+		if re2.Op == opVerticalBar {
+			if n >= 3 {
+				// Now out of reach.
+				// Clean opportunistically.
+				cleanAlt(p.stack[n-3])
+			}
+			p.stack[n-2] = re1
+			p.stack[n-1] = re2
+			return true
+		}
+	}
+	return false
+}
+
+// parseRightParen handles a ) in the input.
+func (p *parser) parseRightParen() error {
+	p.concat()
+	if p.swapVerticalBar() {
+		// pop vertical bar
+		p.stack = p.stack[:len(p.stack)-1]
+	}
+	p.alternate()
+
+	n := len(p.stack)
+	if n < 2 {
+		return &Error{ErrUnexpectedParen, p.wholeRegexp}
+	}
+	re1 := p.stack[n-1]
+	re2 := p.stack[n-2]
+	p.stack = p.stack[:n-2]
+	if re2.Op != opLeftParen {
+		return &Error{ErrUnexpectedParen, p.wholeRegexp}
+	}
+	// Restore flags at time of paren.
+	p.flags = re2.Flags
+	if re2.Cap == 0 {
+		// Just for grouping.
+		p.push(re1)
+	} else {
+		re2.Op = OpCapture
+		re2.Sub = re2.Sub0[:1]
+		re2.Sub[0] = re1
+		p.push(re2)
+	}
+	return nil
+}
+
+// parseEscape parses an escape sequence at the beginning of s
+// and returns the rune.
+func (p *parser) parseEscape(s string) (r rune, rest string, err error) {
+	t := s[1:]
+	if t == "" {
+		return 0, "", &Error{ErrTrailingBackslash, ""}
+	}
+	c, t, err := nextRune(t)
+	if err != nil {
+		return 0, "", err
+	}
+
+Switch:
+	switch c {
+	default:
+		if c < utf8.RuneSelf && !isalnum(c) {
+			// Escaped non-word characters are always themselves.
+			// PCRE is not quite so rigorous: it accepts things like
+			// \q, but we don't. We once rejected \_, but too many
+			// programs and people insist on using it, so allow \_.
+			return c, t, nil
+		}
+
+	// Octal escapes.
+	case '1', '2', '3', '4', '5', '6', '7':
+		// Single non-zero digit is a backreference; not supported
+		if t == "" || t[0] < '0' || t[0] > '7' {
+			break
+		}
+		fallthrough
+	case '0':
+		// Consume up to three octal digits; already have one.
+		r = c - '0'
+		for i := 1; i < 3; i++ {
+			if t == "" || t[0] < '0' || t[0] > '7' {
+				break
+			}
+			r = r*8 + rune(t[0]) - '0'
+			t = t[1:]
+		}
+		return r, t, nil
+
+	// Hexadecimal escapes.
+	case 'x':
+		if t == "" {
+			break
+		}
+		if c, t, err = nextRune(t); err != nil {
+			return 0, "", err
+		}
+		if c == '{' {
+			// Any number of digits in braces.
+			// Perl accepts any text at all; it ignores all text
+			// after the first non-hex digit. We require only hex digits,
+			// and at least one.
+			nhex := 0
+			r = 0
+			for {
+				if t == "" {
+					break Switch
+				}
+				if c, t, err = nextRune(t); err != nil {
+					return 0, "", err
+				}
+				if c == '}' {
+					break
+				}
+				v := unhex(c)
+				if v < 0 {
+					break Switch
+				}
+				r = r*16 + v
+				if r > unicode.MaxRune {
+					break Switch
+				}
+				nhex++
+			}
+			if nhex == 0 {
+				break Switch
+			}
+			return r, t, nil
+		}
+
+		// Easy case: two hex digits.
+		x := unhex(c)
+		if c, t, err = nextRune(t); err != nil {
+			return 0, "", err
+		}
+		y := unhex(c)
+		if x < 0 || y < 0 {
+			break
+		}
+		return x*16 + y, t, nil
+
+	// C escapes. There is no case 'b', to avoid misparsing
+	// the Perl word-boundary \b as the C backspace \b
+	// when in POSIX mode. In Perl, /\b/ means word-boundary
+	// but /[\b]/ means backspace. We don't support that.
+	// If you want a backspace, embed a literal backspace
+	// character or use \x08.
+	case 'a':
+		return '\a', t, err
+	case 'f':
+		return '\f', t, err
+	case 'n':
+		return '\n', t, err
+	case 'r':
+		return '\r', t, err
+	case 't':
+		return '\t', t, err
+	case 'v':
+		return '\v', t, err
+	}
+	return 0, "", &Error{ErrInvalidEscape, s[:len(s)-len(t)]}
+}
+
+// parseClassChar parses a character class character at the beginning of s
+// and returns it.
+func (p *parser) parseClassChar(s, wholeClass string) (r rune, rest string, err error) {
+	if s == "" {
+		return 0, "", &Error{Code: ErrMissingBracket, Expr: wholeClass}
+	}
+
+	// Allow regular escape sequences even though
+	// many need not be escaped in this context.
+	if s[0] == '\\' {
+		return p.parseEscape(s)
+	}
+
+	return nextRune(s)
+}
+
+type charGroup struct {
+	sign  int
+	class []rune
+}
+
+// parsePerlClassEscape parses a leading Perl character class escape like \d
+// from the beginning of s. If one is present, it appends the characters to r
+// and returns the new slice r and the remainder of the string.
+func (p *parser) parsePerlClassEscape(s string, r []rune) (out []rune, rest string) {
+	if p.flags&PerlX == 0 || len(s) < 2 || s[0] != '\\' {
+		return
+	}
+	g := perlGroup[s[0:2]]
+	if g.sign == 0 {
+		return
+	}
+	return p.appendGroup(r, g), s[2:]
+}
+
+// parseNamedClass parses a leading POSIX named character class like [:alnum:]
+// from the beginning of s. If one is present, it appends the characters to r
+// and returns the new slice r and the remainder of the string.
+func (p *parser) parseNamedClass(s string, r []rune) (out []rune, rest string, err error) {
+	if len(s) < 2 || s[0] != '[' || s[1] != ':' {
+		return
+	}
+
+	i := strings.Index(s[2:], ":]")
+	if i < 0 {
+		return
+	}
+	i += 2
+	name, s := s[0:i+2], s[i+2:]
+	g := posixGroup[name]
+	if g.sign == 0 {
+		return nil, "", &Error{ErrInvalidCharRange, name}
+	}
+	return p.appendGroup(r, g), s, nil
+}
+
+func (p *parser) appendGroup(r []rune, g charGroup) []rune {
+	if p.flags&FoldCase == 0 {
+		if g.sign < 0 {
+			r = appendNegatedClass(r, g.class)
+		} else {
+			r = appendClass(r, g.class)
+		}
+	} else {
+		tmp := p.tmpClass[:0]
+		tmp = appendFoldedClass(tmp, g.class)
+		p.tmpClass = tmp
+		tmp = cleanClass(&p.tmpClass)
+		if g.sign < 0 {
+			r = appendNegatedClass(r, tmp)
+		} else {
+			r = appendClass(r, tmp)
+		}
+	}
+	return r
+}
+
+var anyTable = &unicode.RangeTable{
+	R16: []unicode.Range16{{Lo: 0, Hi: 1<<16 - 1, Stride: 1}},
+	R32: []unicode.Range32{{Lo: 1 << 16, Hi: unicode.MaxRune, Stride: 1}},
+}
+
+// unicodeTable returns the unicode.RangeTable identified by name
+// and the table of additional fold-equivalent code points.
+func unicodeTable(name string) (*unicode.RangeTable, *unicode.RangeTable) {
+	// Special case: "Any" means any.
+	if name == "Any" {
+		return anyTable, anyTable
+	}
+	if t := unicode.Categories[name]; t != nil {
+		return t, unicode.FoldCategory[name]
+	}
+	if t := unicode.Scripts[name]; t != nil {
+		return t, unicode.FoldScript[name]
+	}
+	return nil, nil
+}
+
+// parseUnicodeClass parses a leading Unicode character class like \p{Han}
+// from the beginning of s. If one is present, it appends the characters to r
+// and returns the new slice r and the remainder of the string.
+func (p *parser) parseUnicodeClass(s string, r []rune) (out []rune, rest string, err error) {
+	if p.flags&UnicodeGroups == 0 || len(s) < 2 || s[0] != '\\' || s[1] != 'p' && s[1] != 'P' {
+		return
+	}
+
+	// Committed to parse or return error.
+	sign := +1
+	if s[1] == 'P' {
+		sign = -1
+	}
+	t := s[2:]
+	c, t, err := nextRune(t)
+	if err != nil {
+		return
+	}
+	var seq, name string
+	if c != '{' {
+		// Single-letter name.
+		seq = s[:len(s)-len(t)]
+		name = seq[2:]
+	} else {
+		// Name is in braces.
+		end := strings.IndexRune(s, '}')
+		if end < 0 {
+			if err = checkUTF8(s); err != nil {
+				return
+			}
+			return nil, "", &Error{ErrInvalidCharRange, s}
+		}
+		seq, t = s[:end+1], s[end+1:]
+		name = s[3:end]
+		if err = checkUTF8(name); err != nil {
+			return
+		}
+	}
+
+	// Group can have leading negation too.  \p{^Han} == \P{Han}, \P{^Han} == \p{Han}.
+	if name != "" && name[0] == '^' {
+		sign = -sign
+		name = name[1:]
+	}
+
+	tab, fold := unicodeTable(name)
+	if tab == nil {
+		return nil, "", &Error{ErrInvalidCharRange, seq}
+	}
+
+	if p.flags&FoldCase == 0 || fold == nil {
+		if sign > 0 {
+			r = appendTable(r, tab)
+		} else {
+			r = appendNegatedTable(r, tab)
+		}
+	} else {
+		// Merge and clean tab and fold in a temporary buffer.
+		// This is necessary for the negative case and just tidy
+		// for the positive case.
+		tmp := p.tmpClass[:0]
+		tmp = appendTable(tmp, tab)
+		tmp = appendTable(tmp, fold)
+		p.tmpClass = tmp
+		tmp = cleanClass(&p.tmpClass)
+		if sign > 0 {
+			r = appendClass(r, tmp)
+		} else {
+			r = appendNegatedClass(r, tmp)
+		}
+	}
+	return r, t, nil
+}
+
+// parseClass parses a character class at the beginning of s
+// and pushes it onto the parse stack.
+func (p *parser) parseClass(s string) (rest string, err error) {
+	t := s[1:] // chop [
+	re := p.newRegexp(OpCharClass)
+	re.Flags = p.flags
+	re.Rune = re.Rune0[:0]
+
+	sign := +1
+	if t != "" && t[0] == '^' {
+		sign = -1
+		t = t[1:]
+
+		// If character class does not match \n, add it here,
+		// so that negation later will do the right thing.
+		if p.flags&ClassNL == 0 {
+			re.Rune = append(re.Rune, '\n', '\n')
+		}
+	}
+
+	class := re.Rune
+	first := true // ] and - are okay as first char in class
+	for t == "" || t[0] != ']' || first {
+		// POSIX: - is only okay unescaped as first or last in class.
+		// Perl: - is okay anywhere.
+		if t != "" && t[0] == '-' && p.flags&PerlX == 0 && !first && (len(t) == 1 || t[1] != ']') {
+			_, size := utf8.DecodeRuneInString(t[1:])
+			return "", &Error{Code: ErrInvalidCharRange, Expr: t[:1+size]}
+		}
+		first = false
+
+		// Look for POSIX [:alnum:] etc.
+		if len(t) > 2 && t[0] == '[' && t[1] == ':' {
+			nclass, nt, err := p.parseNamedClass(t, class)
+			if err != nil {
+				return "", err
+			}
+			if nclass != nil {
+				class, t = nclass, nt
+				continue
+			}
+		}
+
+		// Look for Unicode character group like \p{Han}.
+		nclass, nt, err := p.parseUnicodeClass(t, class)
+		if err != nil {
+			return "", err
+		}
+		if nclass != nil {
+			class, t = nclass, nt
+			continue
+		}
+
+		// Look for Perl character class symbols (extension).
+		if nclass, nt := p.parsePerlClassEscape(t, class); nclass != nil {
+			class, t = nclass, nt
+			continue
+		}
+
+		// Single character or simple range.
+		rng := t
+		var lo, hi rune
+		if lo, t, err = p.parseClassChar(t, s); err != nil {
+			return "", err
+		}
+		hi = lo
+		// [a-] means (a|-) so check for final ].
+		if len(t) >= 2 && t[0] == '-' && t[1] != ']' {
+			t = t[1:]
+			if hi, t, err = p.parseClassChar(t, s); err != nil {
+				return "", err
+			}
+			if hi < lo {
+				rng = rng[:len(rng)-len(t)]
+				return "", &Error{Code: ErrInvalidCharRange, Expr: rng}
+			}
+		}
+		if p.flags&FoldCase == 0 {
+			class = appendRange(class, lo, hi)
+		} else {
+			class = appendFoldedRange(class, lo, hi)
+		}
+	}
+	t = t[1:] // chop ]
+
+	// Use &re.Rune instead of &class to avoid allocation.
+	re.Rune = class
+	class = cleanClass(&re.Rune)
+	if sign < 0 {
+		class = negateClass(class)
+	}
+	re.Rune = class
+	p.push(re)
+	return t, nil
+}
+
+// cleanClass sorts the ranges (pairs of elements of r),
+// merges them, and eliminates duplicates.
+func cleanClass(rp *[]rune) []rune {
+
+	// Sort by lo increasing, hi decreasing to break ties.
+	sort.Sort(ranges{rp})
+
+	r := *rp
+	if len(r) < 2 {
+		return r
+	}
+
+	// Merge abutting, overlapping.
+	w := 2 // write index
+	for i := 2; i < len(r); i += 2 {
+		lo, hi := r[i], r[i+1]
+		if lo <= r[w-1]+1 {
+			// merge with previous range
+			if hi > r[w-1] {
+				r[w-1] = hi
+			}
+			continue
+		}
+		// new disjoint range
+		r[w] = lo
+		r[w+1] = hi
+		w += 2
+	}
+
+	return r[:w]
+}
+
+// inCharClass reports whether r is in the class.
+// It assumes the class has been cleaned by cleanClass.
+func inCharClass(r rune, class []rune) bool {
+	_, ok := sort.Find(len(class)/2, func(i int) int {
+		lo, hi := class[2*i], class[2*i+1]
+		if r > hi {
+			return +1
+		}
+		if r < lo {
+			return -1
+		}
+		return 0
+	})
+	return ok
+}
+
+// appendLiteral returns the result of appending the literal x to the class r.
+func appendLiteral(r []rune, x rune, flags Flags) []rune {
+	if flags&FoldCase != 0 {
+		return appendFoldedRange(r, x, x)
+	}
+	return appendRange(r, x, x)
+}
+
+// appendRange returns the result of appending the range lo-hi to the class r.
+func appendRange(r []rune, lo, hi rune) []rune {
+	// Expand last range or next to last range if it overlaps or abuts.
+	// Checking two ranges helps when appending case-folded
+	// alphabets, so that one range can be expanding A-Z and the
+	// other expanding a-z.
+	n := len(r)
+	for i := 2; i <= 4; i += 2 { // twice, using i=2, i=4
+		if n >= i {
+			rlo, rhi := r[n-i], r[n-i+1]
+			if lo <= rhi+1 && rlo <= hi+1 {
+				if lo < rlo {
+					r[n-i] = lo
+				}
+				if hi > rhi {
+					r[n-i+1] = hi
+				}
+				return r
+			}
+		}
+	}
+
+	return append(r, lo, hi)
+}
+
+const (
+	// minimum and maximum runes involved in folding.
+	// checked during test.
+	minFold = 0x0041
+	maxFold = 0x1e943
+)
+
+// appendFoldedRange returns the result of appending the range lo-hi
+// and its case folding-equivalent runes to the class r.
+func appendFoldedRange(r []rune, lo, hi rune) []rune {
+	// Optimizations.
+	if lo <= minFold && hi >= maxFold {
+		// Range is full: folding can't add more.
+		return appendRange(r, lo, hi)
+	}
+	if hi < minFold || lo > maxFold {
+		// Range is outside folding possibilities.
+		return appendRange(r, lo, hi)
+	}
+	if lo < minFold {
+		// [lo, minFold-1] needs no folding.
+		r = appendRange(r, lo, minFold-1)
+		lo = minFold
+	}
+	if hi > maxFold {
+		// [maxFold+1, hi] needs no folding.
+		r = appendRange(r, maxFold+1, hi)
+		hi = maxFold
+	}
+
+	// Brute force. Depend on appendRange to coalesce ranges on the fly.
+	for c := lo; c <= hi; c++ {
+		r = appendRange(r, c, c)
+		f := unicode.SimpleFold(c)
+		for f != c {
+			r = appendRange(r, f, f)
+			f = unicode.SimpleFold(f)
+		}
+	}
+	return r
+}
+
+// appendClass returns the result of appending the class x to the class r.
+// It assume x is clean.
+func appendClass(r []rune, x []rune) []rune {
+	for i := 0; i < len(x); i += 2 {
+		r = appendRange(r, x[i], x[i+1])
+	}
+	return r
+}
+
+// appendFoldedClass returns the result of appending the case folding of the class x to the class r.
+func appendFoldedClass(r []rune, x []rune) []rune {
+	for i := 0; i < len(x); i += 2 {
+		r = appendFoldedRange(r, x[i], x[i+1])
+	}
+	return r
+}
+
+// appendNegatedClass returns the result of appending the negation of the class x to the class r.
+// It assumes x is clean.
+func appendNegatedClass(r []rune, x []rune) []rune {
+	nextLo := '\u0000'
+	for i := 0; i < len(x); i += 2 {
+		lo, hi := x[i], x[i+1]
+		if nextLo <= lo-1 {
+			r = appendRange(r, nextLo, lo-1)
+		}
+		nextLo = hi + 1
+	}
+	if nextLo <= unicode.MaxRune {
+		r = appendRange(r, nextLo, unicode.MaxRune)
+	}
+	return r
+}
+
+// appendTable returns the result of appending x to the class r.
+func appendTable(r []rune, x *unicode.RangeTable) []rune {
+	for _, xr := range x.R16 {
+		lo, hi, stride := rune(xr.Lo), rune(xr.Hi), rune(xr.Stride)
+		if stride == 1 {
+			r = appendRange(r, lo, hi)
+			continue
+		}
+		for c := lo; c <= hi; c += stride {
+			r = appendRange(r, c, c)
+		}
+	}
+	for _, xr := range x.R32 {
+		lo, hi, stride := rune(xr.Lo), rune(xr.Hi), rune(xr.Stride)
+		if stride == 1 {
+			r = appendRange(r, lo, hi)
+			continue
+		}
+		for c := lo; c <= hi; c += stride {
+			r = appendRange(r, c, c)
+		}
+	}
+	return r
+}
+
+// appendNegatedTable returns the result of appending the negation of x to the class r.
+func appendNegatedTable(r []rune, x *unicode.RangeTable) []rune {
+	nextLo := '\u0000' // lo end of next class to add
+	for _, xr := range x.R16 {
+		lo, hi, stride := rune(xr.Lo), rune(xr.Hi), rune(xr.Stride)
+		if stride == 1 {
+			if nextLo <= lo-1 {
+				r = appendRange(r, nextLo, lo-1)
+			}
+			nextLo = hi + 1
+			continue
+		}
+		for c := lo; c <= hi; c += stride {
+			if nextLo <= c-1 {
+				r = appendRange(r, nextLo, c-1)
+			}
+			nextLo = c + 1
+		}
+	}
+	for _, xr := range x.R32 {
+		lo, hi, stride := rune(xr.Lo), rune(xr.Hi), rune(xr.Stride)
+		if stride == 1 {
+			if nextLo <= lo-1 {
+				r = appendRange(r, nextLo, lo-1)
+			}
+			nextLo = hi + 1
+			continue
+		}
+		for c := lo; c <= hi; c += stride {
+			if nextLo <= c-1 {
+				r = appendRange(r, nextLo, c-1)
+			}
+			nextLo = c + 1
+		}
+	}
+	if nextLo <= unicode.MaxRune {
+		r = appendRange(r, nextLo, unicode.MaxRune)
+	}
+	return r
+}
+
+// negateClass overwrites r and returns r's negation.
+// It assumes the class r is already clean.
+func negateClass(r []rune) []rune {
+	nextLo := '\u0000' // lo end of next class to add
+	w := 0             // write index
+	for i := 0; i < len(r); i += 2 {
+		lo, hi := r[i], r[i+1]
+		if nextLo <= lo-1 {
+			r[w] = nextLo
+			r[w+1] = lo - 1
+			w += 2
+		}
+		nextLo = hi + 1
+	}
+	r = r[:w]
+	if nextLo <= unicode.MaxRune {
+		// It's possible for the negation to have one more
+		// range - this one - than the original class, so use append.
+		r = append(r, nextLo, unicode.MaxRune)
+	}
+	return r
+}
+
+// ranges implements sort.Interface on a []rune.
+// The choice of receiver type definition is strange
+// but avoids an allocation since we already have
+// a *[]rune.
+type ranges struct {
+	p *[]rune
+}
+
+func (ra ranges) Less(i, j int) bool {
+	p := *ra.p
+	i *= 2
+	j *= 2
+	return p[i] < p[j] || p[i] == p[j] && p[i+1] > p[j+1]
+}
+
+func (ra ranges) Len() int {
+	return len(*ra.p) / 2
+}
+
+func (ra ranges) Swap(i, j int) {
+	p := *ra.p
+	i *= 2
+	j *= 2
+	p[i], p[i+1], p[j], p[j+1] = p[j], p[j+1], p[i], p[i+1]
+}
+
+func checkUTF8(s string) error {
+	for s != "" {
+		rune, size := utf8.DecodeRuneInString(s)
+		if rune == utf8.RuneError && size == 1 {
+			return &Error{Code: ErrInvalidUTF8, Expr: s}
+		}
+		s = s[size:]
+	}
+	return nil
+}
+
+func nextRune(s string) (c rune, t string, err error) {
+	c, size := utf8.DecodeRuneInString(s)
+	if c == utf8.RuneError && size == 1 {
+		return 0, "", &Error{Code: ErrInvalidUTF8, Expr: s}
+	}
+	return c, s[size:], nil
+}
+
+func isalnum(c rune) bool {
+	return '0' <= c && c <= '9' || 'A' <= c && c <= 'Z' || 'a' <= c && c <= 'z'
+}
+
+func unhex(c rune) rune {
+	if '0' <= c && c <= '9' {
+		return c - '0'
+	}
+	if 'a' <= c && c <= 'f' {
+		return c - 'a' + 10
+	}
+	if 'A' <= c && c <= 'F' {
+		return c - 'A' + 10
+	}
+	return -1
+}
diff --git a/src/regexp/syntax/parse_test.go b/src/regexp/syntax/parse_test.go
new file mode 100644
index 0000000..0f885bd
--- /dev/null
+++ b/src/regexp/syntax/parse_test.go
@@ -0,0 +1,628 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+import (
+	"fmt"
+	"strings"
+	"testing"
+	"unicode"
+)
+
+type parseTest struct {
+	Regexp string
+	Dump   string
+}
+
+var parseTests = []parseTest{
+	// Base cases
+	{`a`, `lit{a}`},
+	{`a.`, `cat{lit{a}dot{}}`},
+	{`a.b`, `cat{lit{a}dot{}lit{b}}`},
+	{`ab`, `str{ab}`},
+	{`a.b.c`, `cat{lit{a}dot{}lit{b}dot{}lit{c}}`},
+	{`abc`, `str{abc}`},
+	{`a|^`, `alt{lit{a}bol{}}`},
+	{`a|b`, `cc{0x61-0x62}`},
+	{`(a)`, `cap{lit{a}}`},
+	{`(a)|b`, `alt{cap{lit{a}}lit{b}}`},
+	{`a*`, `star{lit{a}}`},
+	{`a+`, `plus{lit{a}}`},
+	{`a?`, `que{lit{a}}`},
+	{`a{2}`, `rep{2,2 lit{a}}`},
+	{`a{2,3}`, `rep{2,3 lit{a}}`},
+	{`a{2,}`, `rep{2,-1 lit{a}}`},
+	{`a*?`, `nstar{lit{a}}`},
+	{`a+?`, `nplus{lit{a}}`},
+	{`a??`, `nque{lit{a}}`},
+	{`a{2}?`, `nrep{2,2 lit{a}}`},
+	{`a{2,3}?`, `nrep{2,3 lit{a}}`},
+	{`a{2,}?`, `nrep{2,-1 lit{a}}`},
+	// Malformed { } are treated as literals.
+	{`x{1001`, `str{x{1001}`},
+	{`x{9876543210`, `str{x{9876543210}`},
+	{`x{9876543210,`, `str{x{9876543210,}`},
+	{`x{2,1`, `str{x{2,1}`},
+	{`x{1,9876543210`, `str{x{1,9876543210}`},
+	{``, `emp{}`},
+	{`|`, `emp{}`}, // alt{emp{}emp{}} but got factored
+	{`|x|`, `alt{emp{}lit{x}emp{}}`},
+	{`.`, `dot{}`},
+	{`^`, `bol{}`},
+	{`$`, `eol{}`},
+	{`\|`, `lit{|}`},
+	{`\(`, `lit{(}`},
+	{`\)`, `lit{)}`},
+	{`\*`, `lit{*}`},
+	{`\+`, `lit{+}`},
+	{`\?`, `lit{?}`},
+	{`{`, `lit{{}`},
+	{`}`, `lit{}}`},
+	{`\.`, `lit{.}`},
+	{`\^`, `lit{^}`},
+	{`\$`, `lit{$}`},
+	{`\\`, `lit{\}`},
+	{`[ace]`, `cc{0x61 0x63 0x65}`},
+	{`[abc]`, `cc{0x61-0x63}`},
+	{`[a-z]`, `cc{0x61-0x7a}`},
+	{`[a]`, `lit{a}`},
+	{`\-`, `lit{-}`},
+	{`-`, `lit{-}`},
+	{`\_`, `lit{_}`},
+	{`abc`, `str{abc}`},
+	{`abc|def`, `alt{str{abc}str{def}}`},
+	{`abc|def|ghi`, `alt{str{abc}str{def}str{ghi}}`},
+
+	// Posix and Perl extensions
+	{`[[:lower:]]`, `cc{0x61-0x7a}`},
+	{`[a-z]`, `cc{0x61-0x7a}`},
+	{`[^[:lower:]]`, `cc{0x0-0x60 0x7b-0x10ffff}`},
+	{`[[:^lower:]]`, `cc{0x0-0x60 0x7b-0x10ffff}`},
+	{`(?i)[[:lower:]]`, `cc{0x41-0x5a 0x61-0x7a 0x17f 0x212a}`},
+	{`(?i)[a-z]`, `cc{0x41-0x5a 0x61-0x7a 0x17f 0x212a}`},
+	{`(?i)[^[:lower:]]`, `cc{0x0-0x40 0x5b-0x60 0x7b-0x17e 0x180-0x2129 0x212b-0x10ffff}`},
+	{`(?i)[[:^lower:]]`, `cc{0x0-0x40 0x5b-0x60 0x7b-0x17e 0x180-0x2129 0x212b-0x10ffff}`},
+	{`\d`, `cc{0x30-0x39}`},
+	{`\D`, `cc{0x0-0x2f 0x3a-0x10ffff}`},
+	{`\s`, `cc{0x9-0xa 0xc-0xd 0x20}`},
+	{`\S`, `cc{0x0-0x8 0xb 0xe-0x1f 0x21-0x10ffff}`},
+	{`\w`, `cc{0x30-0x39 0x41-0x5a 0x5f 0x61-0x7a}`},
+	{`\W`, `cc{0x0-0x2f 0x3a-0x40 0x5b-0x5e 0x60 0x7b-0x10ffff}`},
+	{`(?i)\w`, `cc{0x30-0x39 0x41-0x5a 0x5f 0x61-0x7a 0x17f 0x212a}`},
+	{`(?i)\W`, `cc{0x0-0x2f 0x3a-0x40 0x5b-0x5e 0x60 0x7b-0x17e 0x180-0x2129 0x212b-0x10ffff}`},
+	{`[^\\]`, `cc{0x0-0x5b 0x5d-0x10ffff}`},
+	//	{ `\C`, `byte{}` },  // probably never
+
+	// Unicode, negatives, and a double negative.
+	{`\p{Braille}`, `cc{0x2800-0x28ff}`},
+	{`\P{Braille}`, `cc{0x0-0x27ff 0x2900-0x10ffff}`},
+	{`\p{^Braille}`, `cc{0x0-0x27ff 0x2900-0x10ffff}`},
+	{`\P{^Braille}`, `cc{0x2800-0x28ff}`},
+	{`\pZ`, `cc{0x20 0xa0 0x1680 0x2000-0x200a 0x2028-0x2029 0x202f 0x205f 0x3000}`},
+	{`[\p{Braille}]`, `cc{0x2800-0x28ff}`},
+	{`[\P{Braille}]`, `cc{0x0-0x27ff 0x2900-0x10ffff}`},
+	{`[\p{^Braille}]`, `cc{0x0-0x27ff 0x2900-0x10ffff}`},
+	{`[\P{^Braille}]`, `cc{0x2800-0x28ff}`},
+	{`[\pZ]`, `cc{0x20 0xa0 0x1680 0x2000-0x200a 0x2028-0x2029 0x202f 0x205f 0x3000}`},
+	{`\p{Lu}`, mkCharClass(unicode.IsUpper)},
+	{`[\p{Lu}]`, mkCharClass(unicode.IsUpper)},
+	{`(?i)[\p{Lu}]`, mkCharClass(isUpperFold)},
+	{`\p{Any}`, `dot{}`},
+	{`\p{^Any}`, `cc{}`},
+
+	// Hex, octal.
+	{`[\012-\234]\141`, `cat{cc{0xa-0x9c}lit{a}}`},
+	{`[\x{41}-\x7a]\x61`, `cat{cc{0x41-0x7a}lit{a}}`},
+
+	// More interesting regular expressions.
+	{`a{,2}`, `str{a{,2}}`},
+	{`\.\^\$\\`, `str{.^$\}`},
+	{`[a-zABC]`, `cc{0x41-0x43 0x61-0x7a}`},
+	{`[^a]`, `cc{0x0-0x60 0x62-0x10ffff}`},
+	{`[α-ε☺]`, `cc{0x3b1-0x3b5 0x263a}`}, // utf-8
+	{`a*{`, `cat{star{lit{a}}lit{{}}`},
+
+	// Test precedences
+	{`(?:ab)*`, `star{str{ab}}`},
+	{`(ab)*`, `star{cap{str{ab}}}`},
+	{`ab|cd`, `alt{str{ab}str{cd}}`},
+	{`a(b|c)d`, `cat{lit{a}cap{cc{0x62-0x63}}lit{d}}`},
+
+	// Test flattening.
+	{`(?:a)`, `lit{a}`},
+	{`(?:ab)(?:cd)`, `str{abcd}`},
+	{`(?:a+b+)(?:c+d+)`, `cat{plus{lit{a}}plus{lit{b}}plus{lit{c}}plus{lit{d}}}`},
+	{`(?:a+|b+)|(?:c+|d+)`, `alt{plus{lit{a}}plus{lit{b}}plus{lit{c}}plus{lit{d}}}`},
+	{`(?:a|b)|(?:c|d)`, `cc{0x61-0x64}`},
+	{`a|.`, `dot{}`},
+	{`.|a`, `dot{}`},
+	{`(?:[abc]|A|Z|hello|world)`, `alt{cc{0x41 0x5a 0x61-0x63}str{hello}str{world}}`},
+	{`(?:[abc]|A|Z)`, `cc{0x41 0x5a 0x61-0x63}`},
+
+	// Test Perl quoted literals
+	{`\Q+|*?{[\E`, `str{+|*?{[}`},
+	{`\Q+\E+`, `plus{lit{+}}`},
+	{`\Qab\E+`, `cat{lit{a}plus{lit{b}}}`},
+	{`\Q\\E`, `lit{\}`},
+	{`\Q\\\E`, `str{\\}`},
+
+	// Test Perl \A and \z
+	{`(?m)^`, `bol{}`},
+	{`(?m)$`, `eol{}`},
+	{`(?-m)^`, `bot{}`},
+	{`(?-m)$`, `eot{}`},
+	{`(?m)\A`, `bot{}`},
+	{`(?m)\z`, `eot{\z}`},
+	{`(?-m)\A`, `bot{}`},
+	{`(?-m)\z`, `eot{\z}`},
+
+	// Test named captures
+	{`(?P<name>a)`, `cap{name:lit{a}}`},
+	{`(?<name>a)`, `cap{name:lit{a}}`},
+
+	// Case-folded literals
+	{`[Aa]`, `litfold{A}`},
+	{`[\x{100}\x{101}]`, `litfold{Ā}`},
+	{`[Δδ]`, `litfold{Δ}`},
+
+	// Strings
+	{`abcde`, `str{abcde}`},
+	{`[Aa][Bb]cd`, `cat{strfold{AB}str{cd}}`},
+
+	// Factoring.
+	{`abc|abd|aef|bcx|bcy`, `alt{cat{lit{a}alt{cat{lit{b}cc{0x63-0x64}}str{ef}}}cat{str{bc}cc{0x78-0x79}}}`},
+	{`ax+y|ax+z|ay+w`, `cat{lit{a}alt{cat{plus{lit{x}}lit{y}}cat{plus{lit{x}}lit{z}}cat{plus{lit{y}}lit{w}}}}`},
+
+	// Bug fixes.
+	{`(?:.)`, `dot{}`},
+	{`(?:x|(?:xa))`, `cat{lit{x}alt{emp{}lit{a}}}`},
+	{`(?:.|(?:.a))`, `cat{dot{}alt{emp{}lit{a}}}`},
+	{`(?:A(?:A|a))`, `cat{lit{A}litfold{A}}`},
+	{`(?:A|a)`, `litfold{A}`},
+	{`A|(?:A|a)`, `litfold{A}`},
+	{`(?s).`, `dot{}`},
+	{`(?-s).`, `dnl{}`},
+	{`(?:(?:^).)`, `cat{bol{}dot{}}`},
+	{`(?-s)(?:(?:^).)`, `cat{bol{}dnl{}}`},
+	{`[\s\S]a`, `cat{cc{0x0-0x10ffff}lit{a}}`},
+
+	// RE2 prefix_tests
+	{`abc|abd`, `cat{str{ab}cc{0x63-0x64}}`},
+	{`a(?:b)c|abd`, `cat{str{ab}cc{0x63-0x64}}`},
+	{`abc|abd|aef|bcx|bcy`,
+		`alt{cat{lit{a}alt{cat{lit{b}cc{0x63-0x64}}str{ef}}}` +
+			`cat{str{bc}cc{0x78-0x79}}}`},
+	{`abc|x|abd`, `alt{str{abc}lit{x}str{abd}}`},
+	{`(?i)abc|ABD`, `cat{strfold{AB}cc{0x43-0x44 0x63-0x64}}`},
+	{`[ab]c|[ab]d`, `cat{cc{0x61-0x62}cc{0x63-0x64}}`},
+	{`.c|.d`, `cat{dot{}cc{0x63-0x64}}`},
+	{`x{2}|x{2}[0-9]`,
+		`cat{rep{2,2 lit{x}}alt{emp{}cc{0x30-0x39}}}`},
+	{`x{2}y|x{2}[0-9]y`,
+		`cat{rep{2,2 lit{x}}alt{lit{y}cat{cc{0x30-0x39}lit{y}}}}`},
+	{`a.*?c|a.*?b`,
+		`cat{lit{a}alt{cat{nstar{dot{}}lit{c}}cat{nstar{dot{}}lit{b}}}}`},
+
+	// Valid repetitions.
+	{`((((((((((x{2}){2}){2}){2}){2}){2}){2}){2}){2}))`, ``},
+	{`((((((((((x{1}){2}){2}){2}){2}){2}){2}){2}){2}){2})`, ``},
+
+	// Valid nesting.
+	{strings.Repeat("(", 999) + strings.Repeat(")", 999), ``},
+	{strings.Repeat("(?:", 999) + strings.Repeat(")*", 999), ``},
+	{"(" + strings.Repeat("|", 12345) + ")", ``}, // not nested at all
+}
+
+const testFlags = MatchNL | PerlX | UnicodeGroups
+
+func TestParseSimple(t *testing.T) {
+	testParseDump(t, parseTests, testFlags)
+}
+
+var foldcaseTests = []parseTest{
+	{`AbCdE`, `strfold{ABCDE}`},
+	{`[Aa]`, `litfold{A}`},
+	{`a`, `litfold{A}`},
+
+	// 0x17F is an old English long s (looks like an f) and folds to s.
+	// 0x212A is the Kelvin symbol and folds to k.
+	{`A[F-g]`, `cat{litfold{A}cc{0x41-0x7a 0x17f 0x212a}}`}, // [Aa][A-z...]
+	{`[[:upper:]]`, `cc{0x41-0x5a 0x61-0x7a 0x17f 0x212a}`},
+	{`[[:lower:]]`, `cc{0x41-0x5a 0x61-0x7a 0x17f 0x212a}`},
+}
+
+func TestParseFoldCase(t *testing.T) {
+	testParseDump(t, foldcaseTests, FoldCase)
+}
+
+var literalTests = []parseTest{
+	{"(|)^$.[*+?]{5,10},\\", "str{(|)^$.[*+?]{5,10},\\}"},
+}
+
+func TestParseLiteral(t *testing.T) {
+	testParseDump(t, literalTests, Literal)
+}
+
+var matchnlTests = []parseTest{
+	{`.`, `dot{}`},
+	{"\n", "lit{\n}"},
+	{`[^a]`, `cc{0x0-0x60 0x62-0x10ffff}`},
+	{`[a\n]`, `cc{0xa 0x61}`},
+}
+
+func TestParseMatchNL(t *testing.T) {
+	testParseDump(t, matchnlTests, MatchNL)
+}
+
+var nomatchnlTests = []parseTest{
+	{`.`, `dnl{}`},
+	{"\n", "lit{\n}"},
+	{`[^a]`, `cc{0x0-0x9 0xb-0x60 0x62-0x10ffff}`},
+	{`[a\n]`, `cc{0xa 0x61}`},
+}
+
+func TestParseNoMatchNL(t *testing.T) {
+	testParseDump(t, nomatchnlTests, 0)
+}
+
+// Test Parse -> Dump.
+func testParseDump(t *testing.T, tests []parseTest, flags Flags) {
+	for _, tt := range tests {
+		re, err := Parse(tt.Regexp, flags)
+		if err != nil {
+			t.Errorf("Parse(%#q): %v", tt.Regexp, err)
+			continue
+		}
+		if tt.Dump == "" {
+			// It parsed. That's all we care about.
+			continue
+		}
+		d := dump(re)
+		if d != tt.Dump {
+			t.Errorf("Parse(%#q).Dump() = %#q want %#q", tt.Regexp, d, tt.Dump)
+		}
+	}
+}
+
+// dump prints a string representation of the regexp showing
+// the structure explicitly.
+func dump(re *Regexp) string {
+	var b strings.Builder
+	dumpRegexp(&b, re)
+	return b.String()
+}
+
+var opNames = []string{
+	OpNoMatch:        "no",
+	OpEmptyMatch:     "emp",
+	OpLiteral:        "lit",
+	OpCharClass:      "cc",
+	OpAnyCharNotNL:   "dnl",
+	OpAnyChar:        "dot",
+	OpBeginLine:      "bol",
+	OpEndLine:        "eol",
+	OpBeginText:      "bot",
+	OpEndText:        "eot",
+	OpWordBoundary:   "wb",
+	OpNoWordBoundary: "nwb",
+	OpCapture:        "cap",
+	OpStar:           "star",
+	OpPlus:           "plus",
+	OpQuest:          "que",
+	OpRepeat:         "rep",
+	OpConcat:         "cat",
+	OpAlternate:      "alt",
+}
+
+// dumpRegexp writes an encoding of the syntax tree for the regexp re to b.
+// It is used during testing to distinguish between parses that might print
+// the same using re's String method.
+func dumpRegexp(b *strings.Builder, re *Regexp) {
+	if int(re.Op) >= len(opNames) || opNames[re.Op] == "" {
+		fmt.Fprintf(b, "op%d", re.Op)
+	} else {
+		switch re.Op {
+		default:
+			b.WriteString(opNames[re.Op])
+		case OpStar, OpPlus, OpQuest, OpRepeat:
+			if re.Flags&NonGreedy != 0 {
+				b.WriteByte('n')
+			}
+			b.WriteString(opNames[re.Op])
+		case OpLiteral:
+			if len(re.Rune) > 1 {
+				b.WriteString("str")
+			} else {
+				b.WriteString("lit")
+			}
+			if re.Flags&FoldCase != 0 {
+				for _, r := range re.Rune {
+					if unicode.SimpleFold(r) != r {
+						b.WriteString("fold")
+						break
+					}
+				}
+			}
+		}
+	}
+	b.WriteByte('{')
+	switch re.Op {
+	case OpEndText:
+		if re.Flags&WasDollar == 0 {
+			b.WriteString(`\z`)
+		}
+	case OpLiteral:
+		for _, r := range re.Rune {
+			b.WriteRune(r)
+		}
+	case OpConcat, OpAlternate:
+		for _, sub := range re.Sub {
+			dumpRegexp(b, sub)
+		}
+	case OpStar, OpPlus, OpQuest:
+		dumpRegexp(b, re.Sub[0])
+	case OpRepeat:
+		fmt.Fprintf(b, "%d,%d ", re.Min, re.Max)
+		dumpRegexp(b, re.Sub[0])
+	case OpCapture:
+		if re.Name != "" {
+			b.WriteString(re.Name)
+			b.WriteByte(':')
+		}
+		dumpRegexp(b, re.Sub[0])
+	case OpCharClass:
+		sep := ""
+		for i := 0; i < len(re.Rune); i += 2 {
+			b.WriteString(sep)
+			sep = " "
+			lo, hi := re.Rune[i], re.Rune[i+1]
+			if lo == hi {
+				fmt.Fprintf(b, "%#x", lo)
+			} else {
+				fmt.Fprintf(b, "%#x-%#x", lo, hi)
+			}
+		}
+	}
+	b.WriteByte('}')
+}
+
+func mkCharClass(f func(rune) bool) string {
+	re := &Regexp{Op: OpCharClass}
+	lo := rune(-1)
+	for i := rune(0); i <= unicode.MaxRune; i++ {
+		if f(i) {
+			if lo < 0 {
+				lo = i
+			}
+		} else {
+			if lo >= 0 {
+				re.Rune = append(re.Rune, lo, i-1)
+				lo = -1
+			}
+		}
+	}
+	if lo >= 0 {
+		re.Rune = append(re.Rune, lo, unicode.MaxRune)
+	}
+	return dump(re)
+}
+
+func isUpperFold(r rune) bool {
+	if unicode.IsUpper(r) {
+		return true
+	}
+	c := unicode.SimpleFold(r)
+	for c != r {
+		if unicode.IsUpper(c) {
+			return true
+		}
+		c = unicode.SimpleFold(c)
+	}
+	return false
+}
+
+func TestFoldConstants(t *testing.T) {
+	last := rune(-1)
+	for i := rune(0); i <= unicode.MaxRune; i++ {
+		if unicode.SimpleFold(i) == i {
+			continue
+		}
+		if last == -1 && minFold != i {
+			t.Errorf("minFold=%#U should be %#U", minFold, i)
+		}
+		last = i
+	}
+	if maxFold != last {
+		t.Errorf("maxFold=%#U should be %#U", maxFold, last)
+	}
+}
+
+func TestAppendRangeCollapse(t *testing.T) {
+	// AppendRange should collapse each of the new ranges
+	// into the earlier ones (it looks back two ranges), so that
+	// the slice never grows very large.
+	// Note that we are not calling cleanClass.
+	var r []rune
+	for i := rune('A'); i <= 'Z'; i++ {
+		r = appendRange(r, i, i)
+		r = appendRange(r, i+'a'-'A', i+'a'-'A')
+	}
+	if string(r) != "AZaz" {
+		t.Errorf("appendRange interlaced A-Z a-z = %s, want AZaz", string(r))
+	}
+}
+
+var invalidRegexps = []string{
+	`(`,
+	`)`,
+	`(a`,
+	`a)`,
+	`(a))`,
+	`(a|b|`,
+	`a|b|)`,
+	`(a|b|))`,
+	`(a|b`,
+	`a|b)`,
+	`(a|b))`,
+	`[a-z`,
+	`([a-z)`,
+	`[a-z)`,
+	`([a-z]))`,
+	`x{1001}`,
+	`x{9876543210}`,
+	`x{2,1}`,
+	`x{1,9876543210}`,
+	"\xff", // Invalid UTF-8
+	"[\xff]",
+	"[\\\xff]",
+	"\\\xff",
+	`(?P<name>a`,
+	`(?P<name>`,
+	`(?P<name`,
+	`(?P<x y>a)`,
+	`(?P<>a)`,
+	`(?<name>a`,
+	`(?<name>`,
+	`(?<name`,
+	`(?<x y>a)`,
+	`(?<>a)`,
+	`[a-Z]`,
+	`(?i)[a-Z]`,
+	`\Q\E*`,
+	`a{100000}`,  // too much repetition
+	`a{100000,}`, // too much repetition
+	"((((((((((x{2}){2}){2}){2}){2}){2}){2}){2}){2}){2})",    // too much repetition
+	strings.Repeat("(", 1000) + strings.Repeat(")", 1000),    // too deep
+	strings.Repeat("(?:", 1000) + strings.Repeat(")*", 1000), // too deep
+	"(" + strings.Repeat("(xx?)", 1000) + "){1000}",          // too long
+	strings.Repeat("(xx?){1000}", 1000),                      // too long
+	strings.Repeat(`\pL`, 27000),                             // too many runes
+}
+
+var onlyPerl = []string{
+	`[a-b-c]`,
+	`\Qabc\E`,
+	`\Q*+?{[\E`,
+	`\Q\\E`,
+	`\Q\\\E`,
+	`\Q\\\\E`,
+	`\Q\\\\\E`,
+	`(?:a)`,
+	`(?P<name>a)`,
+}
+
+var onlyPOSIX = []string{
+	"a++",
+	"a**",
+	"a?*",
+	"a+*",
+	"a{1}*",
+	".{1}{2}.{3}",
+}
+
+func TestParseInvalidRegexps(t *testing.T) {
+	for _, regexp := range invalidRegexps {
+		if re, err := Parse(regexp, Perl); err == nil {
+			t.Errorf("Parse(%#q, Perl) = %s, should have failed", regexp, dump(re))
+		}
+		if re, err := Parse(regexp, POSIX); err == nil {
+			t.Errorf("Parse(%#q, POSIX) = %s, should have failed", regexp, dump(re))
+		}
+	}
+	for _, regexp := range onlyPerl {
+		if _, err := Parse(regexp, Perl); err != nil {
+			t.Errorf("Parse(%#q, Perl): %v", regexp, err)
+		}
+		if re, err := Parse(regexp, POSIX); err == nil {
+			t.Errorf("Parse(%#q, POSIX) = %s, should have failed", regexp, dump(re))
+		}
+	}
+	for _, regexp := range onlyPOSIX {
+		if re, err := Parse(regexp, Perl); err == nil {
+			t.Errorf("Parse(%#q, Perl) = %s, should have failed", regexp, dump(re))
+		}
+		if _, err := Parse(regexp, POSIX); err != nil {
+			t.Errorf("Parse(%#q, POSIX): %v", regexp, err)
+		}
+	}
+}
+
+func TestToStringEquivalentParse(t *testing.T) {
+	for _, tt := range parseTests {
+		re, err := Parse(tt.Regexp, testFlags)
+		if err != nil {
+			t.Errorf("Parse(%#q): %v", tt.Regexp, err)
+			continue
+		}
+		if tt.Dump == "" {
+			// It parsed. That's all we care about.
+			continue
+		}
+		d := dump(re)
+		if d != tt.Dump {
+			t.Errorf("Parse(%#q).Dump() = %#q want %#q", tt.Regexp, d, tt.Dump)
+			continue
+		}
+
+		s := re.String()
+		if s != tt.Regexp {
+			// If ToString didn't return the original regexp,
+			// it must have found one with fewer parens.
+			// Unfortunately we can't check the length here, because
+			// ToString produces "\\{" for a literal brace,
+			// but "{" is a shorter equivalent in some contexts.
+			nre, err := Parse(s, testFlags)
+			if err != nil {
+				t.Errorf("Parse(%#q.String() = %#q): %v", tt.Regexp, s, err)
+				continue
+			}
+			nd := dump(nre)
+			if d != nd {
+				t.Errorf("Parse(%#q) -> %#q; %#q vs %#q", tt.Regexp, s, d, nd)
+			}
+
+			ns := nre.String()
+			if s != ns {
+				t.Errorf("Parse(%#q) -> %#q -> %#q", tt.Regexp, s, ns)
+			}
+		}
+	}
+}
+
+var stringTests = []struct {
+	re  string
+	out string
+}{
+	{`x(?i:ab*c|d?e)1`, `x(?i:AB*C|D?E)1`},
+	{`x(?i:ab*cd?e)1`, `x(?i:AB*CD?E)1`},
+	{`0(?i:ab*c|d?e)1`, `(?i:0(?:AB*C|D?E)1)`},
+	{`0(?i:ab*cd?e)1`, `(?i:0AB*CD?E1)`},
+	{`x(?i:ab*c|d?e)`, `x(?i:AB*C|D?E)`},
+	{`x(?i:ab*cd?e)`, `x(?i:AB*CD?E)`},
+	{`0(?i:ab*c|d?e)`, `(?i:0(?:AB*C|D?E))`},
+	{`0(?i:ab*cd?e)`, `(?i:0AB*CD?E)`},
+	{`(?i:ab*c|d?e)1`, `(?i:(?:AB*C|D?E)1)`},
+	{`(?i:ab*cd?e)1`, `(?i:AB*CD?E1)`},
+	{`(?i:ab)[123](?i:cd)`, `(?i:AB[1-3]CD)`},
+	{`(?i:ab*c|d?e)`, `(?i:AB*C|D?E)`},
+	{`[Aa][Bb]`, `(?i:AB)`},
+	{`[Aa][Bb]*[Cc]`, `(?i:AB*C)`},
+	{`A(?:[Bb][Cc]|[Dd])[Zz]`, `A(?i:(?:BC|D)Z)`},
+	{`[Aa](?:[Bb][Cc]|[Dd])Z`, `(?i:A(?:BC|D))Z`},
+}
+
+func TestString(t *testing.T) {
+	for _, tt := range stringTests {
+		re, err := Parse(tt.re, Perl)
+		if err != nil {
+			t.Errorf("Parse(%#q): %v", tt.re, err)
+			continue
+		}
+		out := re.String()
+		if out != tt.out {
+			t.Errorf("Parse(%#q).String() = %#q, want %#q", tt.re, out, tt.out)
+		}
+	}
+}
diff --git a/src/regexp/syntax/perl_groups.go b/src/regexp/syntax/perl_groups.go
new file mode 100644
index 0000000..effe4e6
--- /dev/null
+++ b/src/regexp/syntax/perl_groups.go
@@ -0,0 +1,134 @@
+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// GENERATED BY make_perl_groups.pl; DO NOT EDIT.
+// make_perl_groups.pl >perl_groups.go
+
+package syntax
+
+var code1 = []rune{ /* \d */
+	0x30, 0x39,
+}
+
+var code2 = []rune{ /* \s */
+	0x9, 0xa,
+	0xc, 0xd,
+	0x20, 0x20,
+}
+
+var code3 = []rune{ /* \w */
+	0x30, 0x39,
+	0x41, 0x5a,
+	0x5f, 0x5f,
+	0x61, 0x7a,
+}
+
+var perlGroup = map[string]charGroup{
+	`\d`: {+1, code1},
+	`\D`: {-1, code1},
+	`\s`: {+1, code2},
+	`\S`: {-1, code2},
+	`\w`: {+1, code3},
+	`\W`: {-1, code3},
+}
+var code4 = []rune{ /* [:alnum:] */
+	0x30, 0x39,
+	0x41, 0x5a,
+	0x61, 0x7a,
+}
+
+var code5 = []rune{ /* [:alpha:] */
+	0x41, 0x5a,
+	0x61, 0x7a,
+}
+
+var code6 = []rune{ /* [:ascii:] */
+	0x0, 0x7f,
+}
+
+var code7 = []rune{ /* [:blank:] */
+	0x9, 0x9,
+	0x20, 0x20,
+}
+
+var code8 = []rune{ /* [:cntrl:] */
+	0x0, 0x1f,
+	0x7f, 0x7f,
+}
+
+var code9 = []rune{ /* [:digit:] */
+	0x30, 0x39,
+}
+
+var code10 = []rune{ /* [:graph:] */
+	0x21, 0x7e,
+}
+
+var code11 = []rune{ /* [:lower:] */
+	0x61, 0x7a,
+}
+
+var code12 = []rune{ /* [:print:] */
+	0x20, 0x7e,
+}
+
+var code13 = []rune{ /* [:punct:] */
+	0x21, 0x2f,
+	0x3a, 0x40,
+	0x5b, 0x60,
+	0x7b, 0x7e,
+}
+
+var code14 = []rune{ /* [:space:] */
+	0x9, 0xd,
+	0x20, 0x20,
+}
+
+var code15 = []rune{ /* [:upper:] */
+	0x41, 0x5a,
+}
+
+var code16 = []rune{ /* [:word:] */
+	0x30, 0x39,
+	0x41, 0x5a,
+	0x5f, 0x5f,
+	0x61, 0x7a,
+}
+
+var code17 = []rune{ /* [:xdigit:] */
+	0x30, 0x39,
+	0x41, 0x46,
+	0x61, 0x66,
+}
+
+var posixGroup = map[string]charGroup{
+	`[:alnum:]`:   {+1, code4},
+	`[:^alnum:]`:  {-1, code4},
+	`[:alpha:]`:   {+1, code5},
+	`[:^alpha:]`:  {-1, code5},
+	`[:ascii:]`:   {+1, code6},
+	`[:^ascii:]`:  {-1, code6},
+	`[:blank:]`:   {+1, code7},
+	`[:^blank:]`:  {-1, code7},
+	`[:cntrl:]`:   {+1, code8},
+	`[:^cntrl:]`:  {-1, code8},
+	`[:digit:]`:   {+1, code9},
+	`[:^digit:]`:  {-1, code9},
+	`[:graph:]`:   {+1, code10},
+	`[:^graph:]`:  {-1, code10},
+	`[:lower:]`:   {+1, code11},
+	`[:^lower:]`:  {-1, code11},
+	`[:print:]`:   {+1, code12},
+	`[:^print:]`:  {-1, code12},
+	`[:punct:]`:   {+1, code13},
+	`[:^punct:]`:  {-1, code13},
+	`[:space:]`:   {+1, code14},
+	`[:^space:]`:  {-1, code14},
+	`[:upper:]`:   {+1, code15},
+	`[:^upper:]`:  {-1, code15},
+	`[:word:]`:    {+1, code16},
+	`[:^word:]`:   {-1, code16},
+	`[:xdigit:]`:  {+1, code17},
+	`[:^xdigit:]`: {-1, code17},
+}
diff --git a/src/regexp/syntax/prog.go b/src/regexp/syntax/prog.go
new file mode 100644
index 0000000..d69ae1a
--- /dev/null
+++ b/src/regexp/syntax/prog.go
@@ -0,0 +1,349 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+import (
+	"strconv"
+	"strings"
+	"unicode"
+	"unicode/utf8"
+)
+
+// Compiled program.
+// May not belong in this package, but convenient for now.
+
+// A Prog is a compiled regular expression program.
+type Prog struct {
+	Inst   []Inst
+	Start  int // index of start instruction
+	NumCap int // number of InstCapture insts in re
+}
+
+// An InstOp is an instruction opcode.
+type InstOp uint8
+
+const (
+	InstAlt InstOp = iota
+	InstAltMatch
+	InstCapture
+	InstEmptyWidth
+	InstMatch
+	InstFail
+	InstNop
+	InstRune
+	InstRune1
+	InstRuneAny
+	InstRuneAnyNotNL
+)
+
+var instOpNames = []string{
+	"InstAlt",
+	"InstAltMatch",
+	"InstCapture",
+	"InstEmptyWidth",
+	"InstMatch",
+	"InstFail",
+	"InstNop",
+	"InstRune",
+	"InstRune1",
+	"InstRuneAny",
+	"InstRuneAnyNotNL",
+}
+
+func (i InstOp) String() string {
+	if uint(i) >= uint(len(instOpNames)) {
+		return ""
+	}
+	return instOpNames[i]
+}
+
+// An EmptyOp specifies a kind or mixture of zero-width assertions.
+type EmptyOp uint8
+
+const (
+	EmptyBeginLine EmptyOp = 1 << iota
+	EmptyEndLine
+	EmptyBeginText
+	EmptyEndText
+	EmptyWordBoundary
+	EmptyNoWordBoundary
+)
+
+// EmptyOpContext returns the zero-width assertions
+// satisfied at the position between the runes r1 and r2.
+// Passing r1 == -1 indicates that the position is
+// at the beginning of the text.
+// Passing r2 == -1 indicates that the position is
+// at the end of the text.
+func EmptyOpContext(r1, r2 rune) EmptyOp {
+	var op EmptyOp = EmptyNoWordBoundary
+	var boundary byte
+	switch {
+	case IsWordChar(r1):
+		boundary = 1
+	case r1 == '\n':
+		op |= EmptyBeginLine
+	case r1 < 0:
+		op |= EmptyBeginText | EmptyBeginLine
+	}
+	switch {
+	case IsWordChar(r2):
+		boundary ^= 1
+	case r2 == '\n':
+		op |= EmptyEndLine
+	case r2 < 0:
+		op |= EmptyEndText | EmptyEndLine
+	}
+	if boundary != 0 { // IsWordChar(r1) != IsWordChar(r2)
+		op ^= (EmptyWordBoundary | EmptyNoWordBoundary)
+	}
+	return op
+}
+
+// IsWordChar reports whether r is considered a “word character”
+// during the evaluation of the \b and \B zero-width assertions.
+// These assertions are ASCII-only: the word characters are [A-Za-z0-9_].
+func IsWordChar(r rune) bool {
+	// Test for lowercase letters first, as these occur more
+	// frequently than uppercase letters in common cases.
+	return 'a' <= r && r <= 'z' || 'A' <= r && r <= 'Z' || '0' <= r && r <= '9' || r == '_'
+}
+
+// An Inst is a single instruction in a regular expression program.
+type Inst struct {
+	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 {
+		i = &p.Inst[i.Out]
+	}
+	return i
+}
+
+// op returns i.Op but merges all the Rune special cases into InstRune
+func (i *Inst) op() InstOp {
+	op := i.Op
+	switch op {
+	case InstRune1, InstRuneAny, InstRuneAnyNotNL:
+		op = InstRune
+	}
+	return op
+}
+
+// Prefix returns a literal string that all matches for the
+// regexp must start with. Complete is true if the prefix
+// is the entire match.
+func (p *Prog) Prefix() (prefix string, complete bool) {
+	i := p.skipNop(uint32(p.Start))
+
+	// Avoid allocation of buffer if prefix is empty.
+	if i.op() != InstRune || len(i.Rune) != 1 {
+		return "", i.Op == InstMatch
+	}
+
+	// Have prefix; gather characters.
+	var buf strings.Builder
+	for i.op() == InstRune && len(i.Rune) == 1 && Flags(i.Arg)&FoldCase == 0 && i.Rune[0] != utf8.RuneError {
+		buf.WriteRune(i.Rune[0])
+		i = p.skipNop(i.Out)
+	}
+	return buf.String(), i.Op == InstMatch
+}
+
+// StartCond returns the leading empty-width conditions that must
+// be true in any match. It returns ^EmptyOp(0) if no matches are possible.
+func (p *Prog) StartCond() EmptyOp {
+	var flag EmptyOp
+	pc := uint32(p.Start)
+	i := &p.Inst[pc]
+Loop:
+	for {
+		switch i.Op {
+		case InstEmptyWidth:
+			flag |= EmptyOp(i.Arg)
+		case InstFail:
+			return ^EmptyOp(0)
+		case InstCapture, InstNop:
+			// skip
+		default:
+			break Loop
+		}
+		pc = i.Out
+		i = &p.Inst[pc]
+	}
+	return flag
+}
+
+const noMatch = -1
+
+// MatchRune reports whether the instruction matches (and consumes) r.
+// It should only be called when i.Op == InstRune.
+func (i *Inst) MatchRune(r rune) bool {
+	return i.MatchRunePos(r) != noMatch
+}
+
+// MatchRunePos checks whether the instruction matches (and consumes) r.
+// If so, MatchRunePos returns the index of the matching rune pair
+// (or, when len(i.Rune) == 1, rune singleton).
+// If not, MatchRunePos returns -1.
+// MatchRunePos should only be called when i.Op == InstRune.
+func (i *Inst) MatchRunePos(r rune) int {
+	rune := i.Rune
+
+	switch len(rune) {
+	case 0:
+		return noMatch
+
+	case 1:
+		// Special case: single-rune slice is from literal string, not char class.
+		r0 := rune[0]
+		if r == r0 {
+			return 0
+		}
+		if Flags(i.Arg)&FoldCase != 0 {
+			for r1 := unicode.SimpleFold(r0); r1 != r0; r1 = unicode.SimpleFold(r1) {
+				if r == r1 {
+					return 0
+				}
+			}
+		}
+		return noMatch
+
+	case 2:
+		if r >= rune[0] && r <= rune[1] {
+			return 0
+		}
+		return noMatch
+
+	case 4, 6, 8:
+		// Linear search for a few pairs.
+		// Should handle ASCII well.
+		for j := 0; j < len(rune); j += 2 {
+			if r < rune[j] {
+				return noMatch
+			}
+			if r <= rune[j+1] {
+				return j / 2
+			}
+		}
+		return noMatch
+	}
+
+	// Otherwise binary search.
+	lo := 0
+	hi := len(rune) / 2
+	for lo < hi {
+		m := int(uint(lo+hi) >> 1)
+		if c := rune[2*m]; c <= r {
+			if r <= rune[2*m+1] {
+				return m
+			}
+			lo = m + 1
+		} else {
+			hi = m
+		}
+	}
+	return noMatch
+}
+
+// MatchEmptyWidth reports whether the instruction matches
+// an empty string between the runes before and after.
+// It should only be called when i.Op == InstEmptyWidth.
+func (i *Inst) MatchEmptyWidth(before rune, after rune) bool {
+	switch EmptyOp(i.Arg) {
+	case EmptyBeginLine:
+		return before == '\n' || before == -1
+	case EmptyEndLine:
+		return after == '\n' || after == -1
+	case EmptyBeginText:
+		return before == -1
+	case EmptyEndText:
+		return after == -1
+	case EmptyWordBoundary:
+		return IsWordChar(before) != IsWordChar(after)
+	case EmptyNoWordBoundary:
+		return IsWordChar(before) == IsWordChar(after)
+	}
+	panic("unknown empty width arg")
+}
+
+func (i *Inst) String() string {
+	var b strings.Builder
+	dumpInst(&b, i)
+	return b.String()
+}
+
+func bw(b *strings.Builder, args ...string) {
+	for _, s := range args {
+		b.WriteString(s)
+	}
+}
+
+func dumpProg(b *strings.Builder, p *Prog) {
+	for j := range p.Inst {
+		i := &p.Inst[j]
+		pc := strconv.Itoa(j)
+		if len(pc) < 3 {
+			b.WriteString("   "[len(pc):])
+		}
+		if j == p.Start {
+			pc += "*"
+		}
+		bw(b, pc, "\t")
+		dumpInst(b, i)
+		bw(b, "\n")
+	}
+}
+
+func u32(i uint32) string {
+	return strconv.FormatUint(uint64(i), 10)
+}
+
+func dumpInst(b *strings.Builder, i *Inst) {
+	switch i.Op {
+	case InstAlt:
+		bw(b, "alt -> ", u32(i.Out), ", ", u32(i.Arg))
+	case InstAltMatch:
+		bw(b, "altmatch -> ", u32(i.Out), ", ", u32(i.Arg))
+	case InstCapture:
+		bw(b, "cap ", u32(i.Arg), " -> ", u32(i.Out))
+	case InstEmptyWidth:
+		bw(b, "empty ", u32(i.Arg), " -> ", u32(i.Out))
+	case InstMatch:
+		bw(b, "match")
+	case InstFail:
+		bw(b, "fail")
+	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))
+	case InstRuneAnyNotNL:
+		bw(b, "anynotnl -> ", u32(i.Out))
+	}
+}
diff --git a/src/regexp/syntax/prog_test.go b/src/regexp/syntax/prog_test.go
new file mode 100644
index 0000000..54dd1dd
--- /dev/null
+++ b/src/regexp/syntax/prog_test.go
@@ -0,0 +1,144 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+import "testing"
+
+var compileTests = []struct {
+	Regexp string
+	Prog   string
+}{
+	{"a", `  0	fail
+  1*	rune1 "a" -> 2
+  2	match
+`},
+	{"[A-M][n-z]", `  0	fail
+  1*	rune "AM" -> 2
+  2	rune "nz" -> 3
+  3	match
+`},
+	{"", `  0	fail
+  1*	nop -> 2
+  2	match
+`},
+	{"a?", `  0	fail
+  1	rune1 "a" -> 3
+  2*	alt -> 1, 3
+  3	match
+`},
+	{"a??", `  0	fail
+  1	rune1 "a" -> 3
+  2*	alt -> 3, 1
+  3	match
+`},
+	{"a+", `  0	fail
+  1*	rune1 "a" -> 2
+  2	alt -> 1, 3
+  3	match
+`},
+	{"a+?", `  0	fail
+  1*	rune1 "a" -> 2
+  2	alt -> 3, 1
+  3	match
+`},
+	{"a*", `  0	fail
+  1	rune1 "a" -> 2
+  2*	alt -> 1, 3
+  3	match
+`},
+	{"a*?", `  0	fail
+  1	rune1 "a" -> 2
+  2*	alt -> 3, 1
+  3	match
+`},
+	{"a+b+", `  0	fail
+  1*	rune1 "a" -> 2
+  2	alt -> 1, 3
+  3	rune1 "b" -> 4
+  4	alt -> 3, 5
+  5	match
+`},
+	{"(a+)(b+)", `  0	fail
+  1*	cap 2 -> 2
+  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
+`},
+	{"(?:|a)+", `  0	fail
+  1	nop -> 4
+  2	rune1 "a" -> 4
+  3*	alt -> 1, 2
+  4	alt -> 3, 5
+  5	match
+`},
+	{"(?:|a)*", `  0	fail
+  1	nop -> 4
+  2	rune1 "a" -> 4
+  3	alt -> 1, 2
+  4	alt -> 3, 6
+  5*	alt -> 3, 6
+  6	match
+`},
+}
+
+func TestCompile(t *testing.T) {
+	for _, tt := range compileTests {
+		re, _ := Parse(tt.Regexp, Perl)
+		p, _ := Compile(re)
+		s := p.String()
+		if s != tt.Prog {
+			t.Errorf("compiled %#q:\n--- have\n%s---\n--- want\n%s---", tt.Regexp, s, tt.Prog)
+		}
+	}
+}
+
+func BenchmarkEmptyOpContext(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		var r1 rune = -1
+		for _, r2 := range "foo, bar, baz\nsome input text.\n" {
+			EmptyOpContext(r1, r2)
+			r1 = r2
+		}
+		EmptyOpContext(r1, -1)
+	}
+}
+
+var sink any
+
+func BenchmarkIsWordChar(b *testing.B) {
+	const chars = "Don't communicate by sharing memory, share memory by communicating."
+	for i := 0; i < b.N; i++ {
+		for _, r := range chars {
+			sink = IsWordChar(r)
+		}
+	}
+	if sink == nil {
+		b.Fatal("Benchmark did not run")
+	}
+	sink = nil
+}
diff --git a/src/regexp/syntax/regexp.go b/src/regexp/syntax/regexp.go
new file mode 100644
index 0000000..4fa7d0e
--- /dev/null
+++ b/src/regexp/syntax/regexp.go
@@ -0,0 +1,477 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+// Note to implementers:
+// In this package, re is always a *Regexp and r is always a rune.
+
+import (
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+// A Regexp is a node in a regular expression syntax tree.
+type Regexp struct {
+	Op       Op // operator
+	Flags    Flags
+	Sub      []*Regexp  // subexpressions, if any
+	Sub0     [1]*Regexp // storage for short Sub
+	Rune     []rune     // matched runes, for OpLiteral, OpCharClass
+	Rune0    [2]rune    // storage for short Rune
+	Min, Max int        // min, max for OpRepeat
+	Cap      int        // capturing index, for OpCapture
+	Name     string     // capturing name, for OpCapture
+}
+
+//go:generate stringer -type Op -trimprefix Op
+
+// An Op is a single regular expression operator.
+type Op uint8
+
+// Operators are listed in precedence order, tightest binding to weakest.
+// Character class operators are listed simplest to most complex
+// (OpLiteral, OpCharClass, OpAnyCharNotNL, OpAnyChar).
+
+const (
+	OpNoMatch        Op = 1 + iota // matches no strings
+	OpEmptyMatch                   // matches empty string
+	OpLiteral                      // matches Runes sequence
+	OpCharClass                    // matches Runes interpreted as range pair list
+	OpAnyCharNotNL                 // matches any character except newline
+	OpAnyChar                      // matches any character
+	OpBeginLine                    // matches empty string at beginning of line
+	OpEndLine                      // matches empty string at end of line
+	OpBeginText                    // matches empty string at beginning of text
+	OpEndText                      // matches empty string at end of text
+	OpWordBoundary                 // matches word boundary `\b`
+	OpNoWordBoundary               // matches word non-boundary `\B`
+	OpCapture                      // capturing subexpression with index Cap, optional name Name
+	OpStar                         // matches Sub[0] zero or more times
+	OpPlus                         // matches Sub[0] one or more times
+	OpQuest                        // matches Sub[0] zero or one times
+	OpRepeat                       // matches Sub[0] at least Min times, at most Max (Max == -1 is no limit)
+	OpConcat                       // matches concatenation of Subs
+	OpAlternate                    // matches alternation of Subs
+)
+
+const opPseudo Op = 128 // where pseudo-ops start
+
+// Equal reports whether x and y have identical structure.
+func (x *Regexp) Equal(y *Regexp) bool {
+	if x == nil || y == nil {
+		return x == y
+	}
+	if x.Op != y.Op {
+		return false
+	}
+	switch x.Op {
+	case OpEndText:
+		// The parse flags remember whether this is \z or \Z.
+		if x.Flags&WasDollar != y.Flags&WasDollar {
+			return false
+		}
+
+	case OpLiteral, OpCharClass:
+		if len(x.Rune) != len(y.Rune) {
+			return false
+		}
+		for i, r := range x.Rune {
+			if r != y.Rune[i] {
+				return false
+			}
+		}
+
+	case OpAlternate, OpConcat:
+		if len(x.Sub) != len(y.Sub) {
+			return false
+		}
+		for i, sub := range x.Sub {
+			if !sub.Equal(y.Sub[i]) {
+				return false
+			}
+		}
+
+	case OpStar, OpPlus, OpQuest:
+		if x.Flags&NonGreedy != y.Flags&NonGreedy || !x.Sub[0].Equal(y.Sub[0]) {
+			return false
+		}
+
+	case OpRepeat:
+		if x.Flags&NonGreedy != y.Flags&NonGreedy || x.Min != y.Min || x.Max != y.Max || !x.Sub[0].Equal(y.Sub[0]) {
+			return false
+		}
+
+	case OpCapture:
+		if x.Cap != y.Cap || x.Name != y.Name || !x.Sub[0].Equal(y.Sub[0]) {
+			return false
+		}
+	}
+	return true
+}
+
+// printFlags is a bit set indicating which flags (including non-capturing parens) to print around a regexp.
+type printFlags uint8
+
+const (
+	flagI    printFlags = 1 << iota // (?i:
+	flagM                           // (?m:
+	flagS                           // (?s:
+	flagOff                         // )
+	flagPrec                        // (?: )
+	negShift = 5                    // flagI<<negShift is (?-i:
+)
+
+// addSpan enables the flags f around start..last,
+// by setting flags[start] = f and flags[last] = flagOff.
+func addSpan(start, last *Regexp, f printFlags, flags *map[*Regexp]printFlags) {
+	if *flags == nil {
+		*flags = make(map[*Regexp]printFlags)
+	}
+	(*flags)[start] = f
+	(*flags)[last] |= flagOff // maybe start==last
+}
+
+// calcFlags calculates the flags to print around each subexpression in re,
+// storing that information in (*flags)[sub] for each affected subexpression.
+// The first time an entry needs to be written to *flags, calcFlags allocates the map.
+// calcFlags also calculates the flags that must be active or can't be active
+// around re and returns those flags.
+func calcFlags(re *Regexp, flags *map[*Regexp]printFlags) (must, cant printFlags) {
+	switch re.Op {
+	default:
+		return 0, 0
+
+	case OpLiteral:
+		// If literal is fold-sensitive, return (flagI, 0) or (0, flagI)
+		// according to whether (?i) is active.
+		// If literal is not fold-sensitive, return 0, 0.
+		for _, r := range re.Rune {
+			if minFold <= r && r <= maxFold && unicode.SimpleFold(r) != r {
+				if re.Flags&FoldCase != 0 {
+					return flagI, 0
+				} else {
+					return 0, flagI
+				}
+			}
+		}
+		return 0, 0
+
+	case OpCharClass:
+		// If literal is fold-sensitive, return 0, flagI - (?i) has been compiled out.
+		// If literal is not fold-sensitive, return 0, 0.
+		for i := 0; i < len(re.Rune); i += 2 {
+			lo := max(minFold, re.Rune[i])
+			hi := min(maxFold, re.Rune[i+1])
+			for r := lo; r <= hi; r++ {
+				for f := unicode.SimpleFold(r); f != r; f = unicode.SimpleFold(f) {
+					if !(lo <= f && f <= hi) && !inCharClass(f, re.Rune) {
+						return 0, flagI
+					}
+				}
+			}
+		}
+		return 0, 0
+
+	case OpAnyCharNotNL: // (?-s).
+		return 0, flagS
+
+	case OpAnyChar: // (?s).
+		return flagS, 0
+
+	case OpBeginLine, OpEndLine: // (?m)^ (?m)$
+		return flagM, 0
+
+	case OpEndText:
+		if re.Flags&WasDollar != 0 { // (?-m)$
+			return 0, flagM
+		}
+		return 0, 0
+
+	case OpCapture, OpStar, OpPlus, OpQuest, OpRepeat:
+		return calcFlags(re.Sub[0], flags)
+
+	case OpConcat, OpAlternate:
+		// Gather the must and cant for each subexpression.
+		// When we find a conflicting subexpression, insert the necessary
+		// flags around the previously identified span and start over.
+		var must, cant, allCant printFlags
+		start := 0
+		last := 0
+		did := false
+		for i, sub := range re.Sub {
+			subMust, subCant := calcFlags(sub, flags)
+			if must&subCant != 0 || subMust&cant != 0 {
+				if must != 0 {
+					addSpan(re.Sub[start], re.Sub[last], must, flags)
+				}
+				must = 0
+				cant = 0
+				start = i
+				did = true
+			}
+			must |= subMust
+			cant |= subCant
+			allCant |= subCant
+			if subMust != 0 {
+				last = i
+			}
+			if must == 0 && start == i {
+				start++
+			}
+		}
+		if !did {
+			// No conflicts: pass the accumulated must and cant upward.
+			return must, cant
+		}
+		if must != 0 {
+			// Conflicts found; need to finish final span.
+			addSpan(re.Sub[start], re.Sub[last], must, flags)
+		}
+		return 0, allCant
+	}
+}
+
+// writeRegexp writes the Perl syntax for the regular expression re to b.
+func writeRegexp(b *strings.Builder, re *Regexp, f printFlags, flags map[*Regexp]printFlags) {
+	f |= flags[re]
+	if f&flagPrec != 0 && f&^(flagOff|flagPrec) != 0 && f&flagOff != 0 {
+		// flagPrec is redundant with other flags being added and terminated
+		f &^= flagPrec
+	}
+	if f&^(flagOff|flagPrec) != 0 {
+		b.WriteString(`(?`)
+		if f&flagI != 0 {
+			b.WriteString(`i`)
+		}
+		if f&flagM != 0 {
+			b.WriteString(`m`)
+		}
+		if f&flagS != 0 {
+			b.WriteString(`s`)
+		}
+		if f&((flagM|flagS)<<negShift) != 0 {
+			b.WriteString(`-`)
+			if f&(flagM<<negShift) != 0 {
+				b.WriteString(`m`)
+			}
+			if f&(flagS<<negShift) != 0 {
+				b.WriteString(`s`)
+			}
+		}
+		b.WriteString(`:`)
+	}
+	if f&flagOff != 0 {
+		defer b.WriteString(`)`)
+	}
+	if f&flagPrec != 0 {
+		b.WriteString(`(?:`)
+		defer b.WriteString(`)`)
+	}
+
+	switch re.Op {
+	default:
+		b.WriteString("<invalid op" + strconv.Itoa(int(re.Op)) + ">")
+	case OpNoMatch:
+		b.WriteString(`[^\x00-\x{10FFFF}]`)
+	case OpEmptyMatch:
+		b.WriteString(`(?:)`)
+	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.
+			// Print the gaps.
+			b.WriteRune('^')
+			for i := 1; i < len(re.Rune)-1; i += 2 {
+				lo, hi := re.Rune[i]+1, re.Rune[i+1]-1
+				escape(b, lo, lo == '-')
+				if lo != hi {
+					if hi != lo+1 {
+						b.WriteRune('-')
+					}
+					escape(b, hi, hi == '-')
+				}
+			}
+		} else {
+			for i := 0; i < len(re.Rune); i += 2 {
+				lo, hi := re.Rune[i], re.Rune[i+1]
+				escape(b, lo, lo == '-')
+				if lo != hi {
+					if hi != lo+1 {
+						b.WriteRune('-')
+					}
+					escape(b, hi, hi == '-')
+				}
+			}
+		}
+		b.WriteRune(']')
+	case OpAnyCharNotNL, OpAnyChar:
+		b.WriteString(`.`)
+	case OpBeginLine:
+		b.WriteString(`^`)
+	case OpEndLine:
+		b.WriteString(`$`)
+	case OpBeginText:
+		b.WriteString(`\A`)
+	case OpEndText:
+		if re.Flags&WasDollar != 0 {
+			b.WriteString(`$`)
+		} else {
+			b.WriteString(`\z`)
+		}
+	case OpWordBoundary:
+		b.WriteString(`\b`)
+	case OpNoWordBoundary:
+		b.WriteString(`\B`)
+	case OpCapture:
+		if re.Name != "" {
+			b.WriteString(`(?P<`)
+			b.WriteString(re.Name)
+			b.WriteRune('>')
+		} else {
+			b.WriteRune('(')
+		}
+		if re.Sub[0].Op != OpEmptyMatch {
+			writeRegexp(b, re.Sub[0], flags[re.Sub[0]], flags)
+		}
+		b.WriteRune(')')
+	case OpStar, OpPlus, OpQuest, OpRepeat:
+		p := printFlags(0)
+		sub := re.Sub[0]
+		if sub.Op > OpCapture || sub.Op == OpLiteral && len(sub.Rune) > 1 {
+			p = flagPrec
+		}
+		writeRegexp(b, sub, p, flags)
+
+		switch re.Op {
+		case OpStar:
+			b.WriteRune('*')
+		case OpPlus:
+			b.WriteRune('+')
+		case OpQuest:
+			b.WriteRune('?')
+		case OpRepeat:
+			b.WriteRune('{')
+			b.WriteString(strconv.Itoa(re.Min))
+			if re.Max != re.Min {
+				b.WriteRune(',')
+				if re.Max >= 0 {
+					b.WriteString(strconv.Itoa(re.Max))
+				}
+			}
+			b.WriteRune('}')
+		}
+		if re.Flags&NonGreedy != 0 {
+			b.WriteRune('?')
+		}
+	case OpConcat:
+		for _, sub := range re.Sub {
+			p := printFlags(0)
+			if sub.Op == OpAlternate {
+				p = flagPrec
+			}
+			writeRegexp(b, sub, p, flags)
+		}
+	case OpAlternate:
+		for i, sub := range re.Sub {
+			if i > 0 {
+				b.WriteRune('|')
+			}
+			writeRegexp(b, sub, 0, flags)
+		}
+	}
+}
+
+func (re *Regexp) String() string {
+	var b strings.Builder
+	var flags map[*Regexp]printFlags
+	must, cant := calcFlags(re, &flags)
+	must |= (cant &^ flagI) << negShift
+	if must != 0 {
+		must |= flagOff
+	}
+	writeRegexp(&b, re, must, flags)
+	return b.String()
+}
+
+const meta = `\.+*?()|[]{}^$`
+
+func escape(b *strings.Builder, r rune, force bool) {
+	if unicode.IsPrint(r) {
+		if strings.ContainsRune(meta, r) || force {
+			b.WriteRune('\\')
+		}
+		b.WriteRune(r)
+		return
+	}
+
+	switch r {
+	case '\a':
+		b.WriteString(`\a`)
+	case '\f':
+		b.WriteString(`\f`)
+	case '\n':
+		b.WriteString(`\n`)
+	case '\r':
+		b.WriteString(`\r`)
+	case '\t':
+		b.WriteString(`\t`)
+	case '\v':
+		b.WriteString(`\v`)
+	default:
+		if r < 0x100 {
+			b.WriteString(`\x`)
+			s := strconv.FormatInt(int64(r), 16)
+			if len(s) == 1 {
+				b.WriteRune('0')
+			}
+			b.WriteString(s)
+			break
+		}
+		b.WriteString(`\x{`)
+		b.WriteString(strconv.FormatInt(int64(r), 16))
+		b.WriteString(`}`)
+	}
+}
+
+// MaxCap walks the regexp to find the maximum capture index.
+func (re *Regexp) MaxCap() int {
+	m := 0
+	if re.Op == OpCapture {
+		m = re.Cap
+	}
+	for _, sub := range re.Sub {
+		if n := sub.MaxCap(); m < n {
+			m = n
+		}
+	}
+	return m
+}
+
+// CapNames walks the regexp to find the names of capturing groups.
+func (re *Regexp) CapNames() []string {
+	names := make([]string, re.MaxCap()+1)
+	re.capNames(names)
+	return names
+}
+
+func (re *Regexp) capNames(names []string) {
+	if re.Op == OpCapture {
+		names[re.Cap] = re.Name
+	}
+	for _, sub := range re.Sub {
+		sub.capNames(names)
+	}
+}
diff --git a/src/regexp/syntax/simplify.go b/src/regexp/syntax/simplify.go
new file mode 100644
index 0000000..e439325
--- /dev/null
+++ b/src/regexp/syntax/simplify.go
@@ -0,0 +1,151 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+// Simplify returns a regexp equivalent to re but without counted repetitions
+// and with various other simplifications, such as rewriting /(?:a+)+/ to /a+/.
+// The resulting regexp will execute correctly but its string representation
+// will not produce the same parse tree, because capturing parentheses
+// may have been duplicated or removed. For example, the simplified form
+// for /(x){1,2}/ is /(x)(x)?/ but both parentheses capture as $1.
+// The returned regexp may share structure with or be the original.
+func (re *Regexp) Simplify() *Regexp {
+	if re == nil {
+		return nil
+	}
+	switch re.Op {
+	case OpCapture, OpConcat, OpAlternate:
+		// Simplify children, building new Regexp if children change.
+		nre := re
+		for i, sub := range re.Sub {
+			nsub := sub.Simplify()
+			if nre == re && nsub != sub {
+				// Start a copy.
+				nre = new(Regexp)
+				*nre = *re
+				nre.Rune = nil
+				nre.Sub = append(nre.Sub0[:0], re.Sub[:i]...)
+			}
+			if nre != re {
+				nre.Sub = append(nre.Sub, nsub)
+			}
+		}
+		return nre
+
+	case OpStar, OpPlus, OpQuest:
+		sub := re.Sub[0].Simplify()
+		return simplify1(re.Op, re.Flags, sub, re)
+
+	case OpRepeat:
+		// Special special case: x{0} matches the empty string
+		// and doesn't even need to consider x.
+		if re.Min == 0 && re.Max == 0 {
+			return &Regexp{Op: OpEmptyMatch}
+		}
+
+		// The fun begins.
+		sub := re.Sub[0].Simplify()
+
+		// x{n,} means at least n matches of x.
+		if re.Max == -1 {
+			// Special case: x{0,} is x*.
+			if re.Min == 0 {
+				return simplify1(OpStar, re.Flags, sub, nil)
+			}
+
+			// Special case: x{1,} is x+.
+			if re.Min == 1 {
+				return simplify1(OpPlus, re.Flags, sub, nil)
+			}
+
+			// General case: x{4,} is xxxx+.
+			nre := &Regexp{Op: OpConcat}
+			nre.Sub = nre.Sub0[:0]
+			for i := 0; i < re.Min-1; i++ {
+				nre.Sub = append(nre.Sub, sub)
+			}
+			nre.Sub = append(nre.Sub, simplify1(OpPlus, re.Flags, sub, nil))
+			return nre
+		}
+
+		// Special case x{0} handled above.
+
+		// Special case: x{1} is just x.
+		if re.Min == 1 && re.Max == 1 {
+			return sub
+		}
+
+		// General case: x{n,m} means n copies of x and m copies of x?
+		// The machine will do less work if we nest the final m copies,
+		// so that x{2,5} = xx(x(x(x)?)?)?
+
+		// Build leading prefix: xx.
+		var prefix *Regexp
+		if re.Min > 0 {
+			prefix = &Regexp{Op: OpConcat}
+			prefix.Sub = prefix.Sub0[:0]
+			for i := 0; i < re.Min; i++ {
+				prefix.Sub = append(prefix.Sub, sub)
+			}
+		}
+
+		// Build and attach suffix: (x(x(x)?)?)?
+		if re.Max > re.Min {
+			suffix := simplify1(OpQuest, re.Flags, sub, nil)
+			for i := re.Min + 1; i < re.Max; i++ {
+				nre2 := &Regexp{Op: OpConcat}
+				nre2.Sub = append(nre2.Sub0[:0], sub, suffix)
+				suffix = simplify1(OpQuest, re.Flags, nre2, nil)
+			}
+			if prefix == nil {
+				return suffix
+			}
+			prefix.Sub = append(prefix.Sub, suffix)
+		}
+		if prefix != nil {
+			return prefix
+		}
+
+		// Some degenerate case like min > max or min < max < 0.
+		// Handle as impossible match.
+		return &Regexp{Op: OpNoMatch}
+	}
+
+	return re
+}
+
+// simplify1 implements Simplify for the unary OpStar,
+// OpPlus, and OpQuest operators. It returns the simple regexp
+// equivalent to
+//
+//	Regexp{Op: op, Flags: flags, Sub: {sub}}
+//
+// under the assumption that sub is already simple, and
+// without first allocating that structure. If the regexp
+// to be returned turns out to be equivalent to re, simplify1
+// returns re instead.
+//
+// simplify1 is factored out of Simplify because the implementation
+// for other operators generates these unary expressions.
+// Letting them call simplify1 makes sure the expressions they
+// generate are simple.
+func simplify1(op Op, flags Flags, sub, re *Regexp) *Regexp {
+	// Special case: repeat the empty string as much as
+	// you want, but it's still the empty string.
+	if sub.Op == OpEmptyMatch {
+		return sub
+	}
+	// The operators are idempotent if the flags match.
+	if op == sub.Op && flags&NonGreedy == sub.Flags&NonGreedy {
+		return sub
+	}
+	if re != nil && re.Op == op && re.Flags&NonGreedy == flags&NonGreedy && sub == re.Sub[0] {
+		return re
+	}
+
+	re = &Regexp{Op: op, Flags: flags}
+	re.Sub = append(re.Sub0[:0], sub)
+	return re
+}
diff --git a/src/regexp/syntax/simplify_test.go b/src/regexp/syntax/simplify_test.go
new file mode 100644
index 0000000..6d06f99
--- /dev/null
+++ b/src/regexp/syntax/simplify_test.go
@@ -0,0 +1,153 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package syntax
+
+import "testing"
+
+var simplifyTests = []struct {
+	Regexp string
+	Simple string
+}{
+	// Already-simple constructs
+	{`a`, `a`},
+	{`ab`, `ab`},
+	{`a|b`, `[ab]`},
+	{`ab|cd`, `ab|cd`},
+	{`(ab)*`, `(ab)*`},
+	{`(ab)+`, `(ab)+`},
+	{`(ab)?`, `(ab)?`},
+	{`.`, `(?s:.)`},
+	{`^`, `(?m:^)`},
+	{`$`, `(?m:$)`},
+	{`[ac]`, `[ac]`},
+	{`[^ac]`, `[^ac]`},
+
+	// Posix character classes
+	{`[[:alnum:]]`, `[0-9A-Za-z]`},
+	{`[[:alpha:]]`, `[A-Za-z]`},
+	{`[[:blank:]]`, `[\t ]`},
+	{`[[:cntrl:]]`, `[\x00-\x1f\x7f]`},
+	{`[[:digit:]]`, `[0-9]`},
+	{`[[:graph:]]`, `[!-~]`},
+	{`[[:lower:]]`, `[a-z]`},
+	{`[[:print:]]`, `[ -~]`},
+	{`[[:punct:]]`, "[!-/:-@\\[-`\\{-~]"},
+	{`[[:space:]]`, `[\t-\r ]`},
+	{`[[:upper:]]`, `[A-Z]`},
+	{`[[:xdigit:]]`, `[0-9A-Fa-f]`},
+
+	// Perl character classes
+	{`\d`, `[0-9]`},
+	{`\s`, `[\t\n\f\r ]`},
+	{`\w`, `[0-9A-Z_a-z]`},
+	{`\D`, `[^0-9]`},
+	{`\S`, `[^\t\n\f\r ]`},
+	{`\W`, `[^0-9A-Z_a-z]`},
+	{`[\d]`, `[0-9]`},
+	{`[\s]`, `[\t\n\f\r ]`},
+	{`[\w]`, `[0-9A-Z_a-z]`},
+	{`[\D]`, `[^0-9]`},
+	{`[\S]`, `[^\t\n\f\r ]`},
+	{`[\W]`, `[^0-9A-Z_a-z]`},
+
+	// Posix repetitions
+	{`a{1}`, `a`},
+	{`a{2}`, `aa`},
+	{`a{5}`, `aaaaa`},
+	{`a{0,1}`, `a?`},
+	// The next three are illegible because Simplify inserts (?:)
+	// parens instead of () parens to avoid creating extra
+	// captured subexpressions. The comments show a version with fewer parens.
+	{`(a){0,2}`, `(?:(a)(a)?)?`},                       //       (aa?)?
+	{`(a){0,4}`, `(?:(a)(?:(a)(?:(a)(a)?)?)?)?`},       //   (a(a(aa?)?)?)?
+	{`(a){2,6}`, `(a)(a)(?:(a)(?:(a)(?:(a)(a)?)?)?)?`}, // aa(a(a(aa?)?)?)?
+	{`a{0,2}`, `(?:aa?)?`},                             //       (aa?)?
+	{`a{0,4}`, `(?:a(?:a(?:aa?)?)?)?`},                 //   (a(a(aa?)?)?)?
+	{`a{2,6}`, `aa(?:a(?:a(?:aa?)?)?)?`},               // aa(a(a(aa?)?)?)?
+	{`a{0,}`, `a*`},
+	{`a{1,}`, `a+`},
+	{`a{2,}`, `aa+`},
+	{`a{5,}`, `aaaaa+`},
+
+	// Test that operators simplify their arguments.
+	{`(?:a{1,}){1,}`, `a+`},
+	{`(a{1,}b{1,})`, `(a+b+)`},
+	{`a{1,}|b{1,}`, `a+|b+`},
+	{`(?:a{1,})*`, `(?:a+)*`},
+	{`(?:a{1,})+`, `a+`},
+	{`(?:a{1,})?`, `(?:a+)?`},
+	{``, `(?:)`},
+	{`a{0}`, `(?:)`},
+
+	// Character class simplification
+	{`[ab]`, `[ab]`},
+	{`[abc]`, `[a-c]`},
+	{`[a-za-za-z]`, `[a-z]`},
+	{`[A-Za-zA-Za-z]`, `[A-Za-z]`},
+	{`[ABCDEFGH]`, `[A-H]`},
+	{`[AB-CD-EF-GH]`, `[A-H]`},
+	{`[W-ZP-XE-R]`, `[E-Z]`},
+	{`[a-ee-gg-m]`, `[a-m]`},
+	{`[a-ea-ha-m]`, `[a-m]`},
+	{`[a-ma-ha-e]`, `[a-m]`},
+	{`[a-zA-Z0-9 -~]`, `[ -~]`},
+
+	// Empty character classes
+	{`[^[:cntrl:][:^cntrl:]]`, `[^\x00-\x{10FFFF}]`},
+
+	// Full character classes
+	{`[[:cntrl:][:^cntrl:]]`, `(?s:.)`},
+
+	// Unicode case folding.
+	{`(?i)A`, `(?i:A)`},
+	{`(?i)a`, `(?i:A)`},
+	{`(?i)[A]`, `(?i:A)`},
+	{`(?i)[a]`, `(?i:A)`},
+	{`(?i)K`, `(?i:K)`},
+	{`(?i)k`, `(?i:K)`},
+	{`(?i)\x{212a}`, "(?i:K)"},
+	{`(?i)[K]`, "[Kk\u212A]"},
+	{`(?i)[k]`, "[Kk\u212A]"},
+	{`(?i)[\x{212a}]`, "[Kk\u212A]"},
+	{`(?i)[a-z]`, "[A-Za-z\u017F\u212A]"},
+	{`(?i)[\x00-\x{FFFD}]`, "[\\x00-\uFFFD]"},
+	{`(?i)[\x00-\x{10FFFF}]`, `(?s:.)`},
+
+	// Empty string as a regular expression.
+	// The empty string must be preserved inside parens in order
+	// to make submatches work right, so these tests are less
+	// interesting than they might otherwise be. String inserts
+	// explicit (?:) in place of non-parenthesized empty strings,
+	// to make them easier to spot for other parsers.
+	{`(a|b|c|)`, `([a-c]|(?:))`},
+	{`(a|b|)`, `([ab]|(?:))`},
+	{`(|)`, `()`},
+	{`a()`, `a()`},
+	{`(()|())`, `(()|())`},
+	{`(a|)`, `(a|(?:))`},
+	{`ab()cd()`, `ab()cd()`},
+	{`()`, `()`},
+	{`()*`, `()*`},
+	{`()+`, `()+`},
+	{`()?`, `()?`},
+	{`(){0}`, `(?:)`},
+	{`(){1}`, `()`},
+	{`(){1,}`, `()+`},
+	{`(){0,2}`, `(?:()()?)?`},
+}
+
+func TestSimplify(t *testing.T) {
+	for _, tt := range simplifyTests {
+		re, err := Parse(tt.Regexp, MatchNL|Perl&^OneLine)
+		if err != nil {
+			t.Errorf("Parse(%#q) = error %v", tt.Regexp, err)
+			continue
+		}
+		s := re.Simplify().String()
+		if s != tt.Simple {
+			t.Errorf("Simplify(%#q) = %#q, want %#q", tt.Regexp, s, tt.Simple)
+		}
+	}
+}
diff --git a/src/regexp/testdata/README b/src/regexp/testdata/README
new file mode 100644
index 0000000..58cec82
--- /dev/null
+++ b/src/regexp/testdata/README
@@ -0,0 +1,24 @@
+AT&T POSIX Test Files
+See textregex.c for copyright + license.
+
+testregex.c	http://www2.research.att.com/~gsf/testregex/testregex.c
+basic.dat	http://www2.research.att.com/~gsf/testregex/basic.dat
+nullsubexpr.dat	http://www2.research.att.com/~gsf/testregex/nullsubexpr.dat
+repetition.dat	http://www2.research.att.com/~gsf/testregex/repetition.dat
+
+The test data has been edited to reflect RE2/Go differences:
+  * In a star of a possibly empty match like (a*)* matching x,
+    the no match case runs the starred subexpression zero times,
+    not once.  This is consistent with (a*)* matching a, which
+    runs the starred subexpression one time, not twice.
+  * The submatch choice is first match, not the POSIX rule.
+
+Such changes are marked with 'RE2/Go'.
+
+
+RE2 Test Files
+
+re2-exhaustive.txt.bz2 and re2-search.txt are built by running
+'make log' in the RE2 distribution https://github.com/google/re2/
+
+The exhaustive file is compressed because it is huge.
diff --git a/src/regexp/testdata/basic.dat b/src/regexp/testdata/basic.dat
new file mode 100644
index 0000000..1776b1f
--- /dev/null
+++ b/src/regexp/testdata/basic.dat
@@ -0,0 +1,217 @@
+NOTE	all standard compliant implementations should pass these : 2002-05-31
+
+BE	abracadabra$	abracadabracadabra	(7,18)
+BE	a...b		abababbb		(2,7)
+BE	XXXXXX		..XXXXXX		(2,8)
+E	\)		()	(1,2)
+BE	a]		a]a	(0,2)
+B	}		}	(0,1)
+E	\}		}	(0,1)
+BE	\]		]	(0,1)
+B	]		]	(0,1)
+E	]		]	(0,1)
+B	{		{	(0,1)
+B	}		}	(0,1)
+BE	^a		ax	(0,1)
+BE	\^a		a^a	(1,3)
+BE	a\^		a^	(0,2)
+BE	a$		aa	(1,2)
+BE	a\$		a$	(0,2)
+BE	^$		NULL	(0,0)
+E	$^		NULL	(0,0)
+E	a($)		aa	(1,2)(2,2)
+E	a*(^a)		aa	(0,1)(0,1)
+E	(..)*(...)*		a	(0,0)
+E	(..)*(...)*		abcd	(0,4)(2,4)
+E	(ab|a)(bc|c)		abc	(0,3)(0,2)(2,3)
+E	(ab)c|abc		abc	(0,3)(0,2)
+E	a{0}b		ab			(1,2)
+E	(a*)(b?)(b+)b{3}	aaabbbbbbb	(0,10)(0,3)(3,4)(4,7)
+E	(a*)(b{0,1})(b{1,})b{3}	aaabbbbbbb	(0,10)(0,3)(3,4)(4,7)
+E	a{9876543210}	NULL	BADBR
+E	((a|a)|a)			a	(0,1)(0,1)(0,1)
+E	(a*)(a|aa)			aaaa	(0,4)(0,3)(3,4)
+E	a*(a.|aa)			aaaa	(0,4)(2,4)
+E	a(b)|c(d)|a(e)f			aef	(0,3)(?,?)(?,?)(1,2)
+E	(a|b)?.*			b	(0,1)(0,1)
+E	(a|b)c|a(b|c)			ac	(0,2)(0,1)
+E	(a|b)c|a(b|c)			ab	(0,2)(?,?)(1,2)
+E	(a|b)*c|(a|ab)*c		abc	(0,3)(1,2)
+E	(a|b)*c|(a|ab)*c		xc	(1,2)
+E	(.a|.b).*|.*(.a|.b)		xa	(0,2)(0,2)
+E	a?(ab|ba)ab			abab	(0,4)(0,2)
+E	a?(ac{0}b|ba)ab			abab	(0,4)(0,2)
+E	ab|abab				abbabab	(0,2)
+E	aba|bab|bba			baaabbbaba	(5,8)
+E	aba|bab				baaabbbaba	(6,9)
+E	(aa|aaa)*|(a|aaaaa)		aa	(0,2)(0,2)
+E	(a.|.a.)*|(a|.a...)		aa	(0,2)(0,2)
+E	ab|a				xabc	(1,3)
+E	ab|a				xxabc	(2,4)
+Ei	(Ab|cD)*			aBcD	(0,4)(2,4)
+BE	[^-]			--a		(2,3)
+BE	[a-]*			--a		(0,3)
+BE	[a-m-]*			--amoma--	(0,4)
+E	:::1:::0:|:::1:1:0:	:::0:::1:::1:::0:	(8,17)
+E	:::1:::0:|:::1:1:1:	:::0:::1:::1:::0:	(8,17)
+{E	[[:upper:]]		A		(0,1)	[[<element>]] not supported
+E	[[:lower:]]+		`az{		(1,3)
+E	[[:upper:]]+		@AZ[		(1,3)
+# No collation in Go
+#BE	[[-]]			[[-]]		(2,4)
+#BE	[[.NIL.]]	NULL	ECOLLATE
+#BE	[[=aleph=]]	NULL	ECOLLATE
+}
+BE$	\n		\n	(0,1)
+BEn$	\n		\n	(0,1)
+BE$	[^a]		\n	(0,1)
+BE$	\na		\na	(0,2)
+E	(a)(b)(c)	abc	(0,3)(0,1)(1,2)(2,3)
+BE	xxx		xxx	(0,3)
+E1	(^|[ (,;])((([Ff]eb[^ ]* *|0*2/|\* */?)0*[6-7]))([^0-9]|$)	feb 6,	(0,6)
+E1	(^|[ (,;])((([Ff]eb[^ ]* *|0*2/|\* */?)0*[6-7]))([^0-9]|$)	2/7	(0,3)
+E1	(^|[ (,;])((([Ff]eb[^ ]* *|0*2/|\* */?)0*[6-7]))([^0-9]|$)	feb 1,Feb 6	(5,11)
+E3	((((((((((((((((((((((((((((((x))))))))))))))))))))))))))))))	x	(0,1)(0,1)(0,1)
+E3	((((((((((((((((((((((((((((((x))))))))))))))))))))))))))))))*	xx	(0,2)(1,2)(1,2)
+E	a?(ab|ba)*	ababababababababababababababababababababababababababababababababababababababababa	(0,81)(79,81)
+E	abaa|abbaa|abbbaa|abbbbaa	ababbabbbabbbabbbbabbbbaa	(18,25)
+E	abaa|abbaa|abbbaa|abbbbaa	ababbabbbabbbabbbbabaa	(18,22)
+E	aaac|aabc|abac|abbc|baac|babc|bbac|bbbc	baaabbbabac	(7,11)
+BE$	.*			\x01\xff	(0,2)
+E	aaaa|bbbb|cccc|ddddd|eeeeee|fffffff|gggg|hhhh|iiiii|jjjjj|kkkkk|llll		XaaaXbbbXcccXdddXeeeXfffXgggXhhhXiiiXjjjXkkkXlllXcbaXaaaa	(53,57)
+L	aaaa\nbbbb\ncccc\nddddd\neeeeee\nfffffff\ngggg\nhhhh\niiiii\njjjjj\nkkkkk\nllll		XaaaXbbbXcccXdddXeeeXfffXgggXhhhXiiiXjjjXkkkXlllXcbaXaaaa	NOMATCH
+E	a*a*a*a*a*b		aaaaaaaaab	(0,10)
+BE	^			NULL		(0,0)
+BE	$			NULL		(0,0)
+BE	^$			NULL		(0,0)
+BE	^a$			a		(0,1)
+BE	abc			abc		(0,3)
+BE	abc			xabcy		(1,4)
+BE	abc			ababc		(2,5)
+BE	ab*c			abc		(0,3)
+BE	ab*bc			abc		(0,3)
+BE	ab*bc			abbc		(0,4)
+BE	ab*bc			abbbbc		(0,6)
+E	ab+bc			abbc		(0,4)
+E	ab+bc			abbbbc		(0,6)
+E	ab?bc			abbc		(0,4)
+E	ab?bc			abc		(0,3)
+E	ab?c			abc		(0,3)
+BE	^abc$			abc		(0,3)
+BE	^abc			abcc		(0,3)
+BE	abc$			aabc		(1,4)
+BE	^			abc		(0,0)
+BE	$			abc		(3,3)
+BE	a.c			abc		(0,3)
+BE	a.c			axc		(0,3)
+BE	a.*c			axyzc		(0,5)
+BE	a[bc]d			abd		(0,3)
+BE	a[b-d]e			ace		(0,3)
+BE	a[b-d]			aac		(1,3)
+BE	a[-b]			a-		(0,2)
+BE	a[b-]			a-		(0,2)
+BE	a]			a]		(0,2)
+BE	a[]]b			a]b		(0,3)
+BE	a[^bc]d			aed		(0,3)
+BE	a[^-b]c			adc		(0,3)
+BE	a[^]b]c			adc		(0,3)
+E	ab|cd			abc		(0,2)
+E	ab|cd			abcd		(0,2)
+E	a\(b			a(b		(0,3)
+E	a\(*b			ab		(0,2)
+E	a\(*b			a((b		(0,4)
+E	((a))			abc		(0,1)(0,1)(0,1)
+E	(a)b(c)			abc		(0,3)(0,1)(2,3)
+E	a+b+c			aabbabc		(4,7)
+E	a*			aaa		(0,3)
+E	(a*)*			-		(0,0)(0,0)
+E	(a*)+			-		(0,0)(0,0)
+E	(a*|b)*			-		(0,0)(0,0)
+E	(a+|b)*			ab		(0,2)(1,2)
+E	(a+|b)+			ab		(0,2)(1,2)
+E	(a+|b)?			ab		(0,1)(0,1)
+BE	[^ab]*			cde		(0,3)
+E	(^)*			-		(0,0)(0,0)
+BE	a*			NULL		(0,0)
+E	([abc])*d		abbbcd		(0,6)(4,5)
+E	([abc])*bcd		abcd		(0,4)(0,1)
+E	a|b|c|d|e		e		(0,1)
+E	(a|b|c|d|e)f		ef		(0,2)(0,1)
+E	((a*|b))*		-		(0,0)(0,0)(0,0)
+BE	abcd*efg		abcdefg		(0,7)
+BE	ab*			xabyabbbz	(1,3)
+BE	ab*			xayabbbz	(1,2)
+E	(ab|cd)e		abcde		(2,5)(2,4)
+BE	[abhgefdc]ij		hij		(0,3)
+E	(a|b)c*d		abcd		(1,4)(1,2)
+E	(ab|ab*)bc		abc		(0,3)(0,1)
+E	a([bc]*)c*		abc		(0,3)(1,3)
+E	a([bc]*)(c*d)		abcd		(0,4)(1,3)(3,4)
+E	a([bc]+)(c*d)		abcd		(0,4)(1,3)(3,4)
+E	a([bc]*)(c+d)		abcd		(0,4)(1,2)(2,4)
+E	a[bcd]*dcdcde		adcdcde		(0,7)
+E	(ab|a)b*c		abc		(0,3)(0,2)
+E	((a)(b)c)(d)		abcd		(0,4)(0,3)(0,1)(1,2)(3,4)
+BE	[A-Za-z_][A-Za-z0-9_]*	alpha		(0,5)
+E	^a(bc+|b[eh])g|.h$	abh		(1,3)
+E	(bc+d$|ef*g.|h?i(j|k))	effgz		(0,5)(0,5)
+E	(bc+d$|ef*g.|h?i(j|k))	ij		(0,2)(0,2)(1,2)
+E	(bc+d$|ef*g.|h?i(j|k))	reffgz		(1,6)(1,6)
+E	(((((((((a)))))))))	a		(0,1)(0,1)(0,1)(0,1)(0,1)(0,1)(0,1)(0,1)(0,1)(0,1)
+BE	multiple words		multiple words yeah	(0,14)
+E	(.*)c(.*)		abcde		(0,5)(0,2)(3,5)
+BE	abcd			abcd		(0,4)
+E	a(bc)d			abcd		(0,4)(1,3)
+E	a[
-]?c		ac		(0,3)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Qaddafi	(0,15)(?,?)(10,12)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Mo'ammar Gadhafi	(0,16)(?,?)(11,13)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Kaddafi	(0,15)(?,?)(10,12)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Qadhafi	(0,15)(?,?)(10,12)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Gadafi	(0,14)(?,?)(10,11)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Mu'ammar Qadafi	(0,15)(?,?)(11,12)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Moamar Gaddafi	(0,14)(?,?)(9,11)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Mu'ammar Qadhdhafi	(0,18)(?,?)(13,15)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Khaddafi	(0,16)(?,?)(11,13)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Ghaddafy	(0,16)(?,?)(11,13)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Ghadafi	(0,15)(?,?)(11,12)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Ghaddafi	(0,16)(?,?)(11,13)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muamar Kaddafi	(0,14)(?,?)(9,11)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Quathafi	(0,16)(?,?)(11,13)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Muammar Gheddafi	(0,16)(?,?)(11,13)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Moammar Khadafy	(0,15)(?,?)(11,12)
+E	M[ou]'?am+[ae]r .*([AEae]l[- ])?[GKQ]h?[aeu]+([dtz][dhz]?)+af[iy]	Moammar Qudhafi	(0,15)(?,?)(10,12)
+E	a+(b|c)*d+		aabcdd			(0,6)(3,4)
+E	^.+$			vivi			(0,4)
+E	^(.+)$			vivi			(0,4)(0,4)
+E	^([^!.]+).att.com!(.+)$	gryphon.att.com!eby	(0,19)(0,7)(16,19)
+E	^([^!]+!)?([^!]+)$	bas			(0,3)(?,?)(0,3)
+E	^([^!]+!)?([^!]+)$	bar!bas			(0,7)(0,4)(4,7)
+E	^([^!]+!)?([^!]+)$	foo!bas			(0,7)(0,4)(4,7)
+E	^.+!([^!]+!)([^!]+)$	foo!bar!bas		(0,11)(4,8)(8,11)
+E	((foo)|(bar))!bas	bar!bas			(0,7)(0,3)(?,?)(0,3)
+E	((foo)|(bar))!bas	foo!bar!bas		(4,11)(4,7)(?,?)(4,7)
+E	((foo)|(bar))!bas	foo!bas			(0,7)(0,3)(0,3)
+E	((foo)|bar)!bas		bar!bas			(0,7)(0,3)
+E	((foo)|bar)!bas		foo!bar!bas		(4,11)(4,7)
+E	((foo)|bar)!bas		foo!bas			(0,7)(0,3)(0,3)
+E	(foo|(bar))!bas		bar!bas			(0,7)(0,3)(0,3)
+E	(foo|(bar))!bas		foo!bar!bas		(4,11)(4,7)(4,7)
+E	(foo|(bar))!bas		foo!bas			(0,7)(0,3)
+E	(foo|bar)!bas		bar!bas			(0,7)(0,3)
+E	(foo|bar)!bas		foo!bar!bas		(4,11)(4,7)
+E	(foo|bar)!bas		foo!bas			(0,7)(0,3)
+E	^(([^!]+!)?([^!]+)|.+!([^!]+!)([^!]+))$	foo!bar!bas	(0,11)(0,11)(?,?)(?,?)(4,8)(8,11)
+E	^([^!]+!)?([^!]+)$|^.+!([^!]+!)([^!]+)$	bas		(0,3)(?,?)(0,3)
+E	^([^!]+!)?([^!]+)$|^.+!([^!]+!)([^!]+)$	bar!bas		(0,7)(0,4)(4,7)
+E	^([^!]+!)?([^!]+)$|^.+!([^!]+!)([^!]+)$	foo!bar!bas	(0,11)(?,?)(?,?)(4,8)(8,11)
+E	^([^!]+!)?([^!]+)$|^.+!([^!]+!)([^!]+)$	foo!bas		(0,7)(0,4)(4,7)
+E	^(([^!]+!)?([^!]+)|.+!([^!]+!)([^!]+))$	bas		(0,3)(0,3)(?,?)(0,3)
+E	^(([^!]+!)?([^!]+)|.+!([^!]+!)([^!]+))$	bar!bas		(0,7)(0,7)(0,4)(4,7)
+E	^(([^!]+!)?([^!]+)|.+!([^!]+!)([^!]+))$	foo!bar!bas	(0,11)(0,11)(?,?)(?,?)(4,8)(8,11)
+E	^(([^!]+!)?([^!]+)|.+!([^!]+!)([^!]+))$	foo!bas		(0,7)(0,7)(0,4)(4,7)
+E	.*(/XXX).*			/XXX			(0,4)(0,4)
+E	.*(\\XXX).*			\XXX			(0,4)(0,4)
+E	\\XXX				\XXX			(0,4)
+E	.*(/000).*			/000			(0,4)(0,4)
+E	.*(\\000).*			\000			(0,4)(0,4)
+E	\\000				\000			(0,4)
diff --git a/src/regexp/testdata/nullsubexpr.dat b/src/regexp/testdata/nullsubexpr.dat
new file mode 100644
index 0000000..99ce0f5
--- /dev/null
+++ b/src/regexp/testdata/nullsubexpr.dat
@@ -0,0 +1,73 @@
+NOTE	null subexpression matches : 2002-06-06
+
+E	(a*)*		a		(0,1)(0,1)
+E	SAME		x		(0,0)(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	(a*)+		a		(0,1)(0,1)
+E	SAME		x		(0,0)(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	(a+)*		a		(0,1)(0,1)
+E	SAME		x		(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	(a+)+		a		(0,1)(0,1)
+E	SAME		x		NOMATCH
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+
+E	([a]*)*		a		(0,1)(0,1)
+E	SAME		x		(0,0)(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	([a]*)+		a		(0,1)(0,1)
+E	SAME		x		(0,0)(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaax		(0,6)(0,6)
+E	([^b]*)*	a		(0,1)(0,1)
+E	SAME		b		(0,0)(0,0)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		aaaaaab		(0,6)(0,6)
+E	([ab]*)*	a		(0,1)(0,1)
+E	SAME		aaaaaa		(0,6)(0,6)
+E	SAME		ababab		(0,6)(0,6)
+E	SAME		bababa		(0,6)(0,6)
+E	SAME		b		(0,1)(0,1)
+E	SAME		bbbbbb		(0,6)(0,6)
+E	SAME		aaaabcde	(0,5)(0,5)
+E	([^a]*)*	b		(0,1)(0,1)
+E	SAME		bbbbbb		(0,6)(0,6)
+E	SAME		aaaaaa		(0,0)(0,0)
+E	([^ab]*)*	ccccxx		(0,6)(0,6)
+E	SAME		ababab		(0,0)(0,0)
+
+E	((z)+|a)*	zabcde		(0,2)(1,2)
+
+#{E	a+?		aaaaaa		(0,1)	no *? +? minimal match ops
+#E	(a)		aaa		(0,1)(0,1)
+#E	(a*?)		aaa		(0,0)(0,0)
+#E	(a)*?		aaa		(0,0)
+#E	(a*?)*?		aaa		(0,0)
+#}
+
+B	\(a*\)*\(x\)		x	(0,1)(0,0)(0,1)
+B	\(a*\)*\(x\)		ax	(0,2)(0,1)(1,2)
+B	\(a*\)*\(x\)		axa	(0,2)(0,1)(1,2)
+B	\(a*\)*\(x\)\(\1\)	x	(0,1)(0,0)(0,1)(1,1)
+B	\(a*\)*\(x\)\(\1\)	ax	(0,2)(1,1)(1,2)(2,2)
+B	\(a*\)*\(x\)\(\1\)	axa	(0,3)(0,1)(1,2)(2,3)
+B	\(a*\)*\(x\)\(\1\)\(x\)	axax	(0,4)(0,1)(1,2)(2,3)(3,4)
+B	\(a*\)*\(x\)\(\1\)\(x\)	axxa	(0,3)(1,1)(1,2)(2,2)(2,3)
+
+E	(a*)*(x)		x	(0,1)(0,0)(0,1)
+E	(a*)*(x)		ax	(0,2)(0,1)(1,2)
+E	(a*)*(x)		axa	(0,2)(0,1)(1,2)
+
+E	(a*)+(x)		x	(0,1)(0,0)(0,1)
+E	(a*)+(x)		ax	(0,2)(0,1)(1,2)
+E	(a*)+(x)		axa	(0,2)(0,1)(1,2)
+
+E	(a*){2}(x)		x	(0,1)(0,0)(0,1)
+E	(a*){2}(x)		ax	(0,2)(1,1)(1,2)
+E	(a*){2}(x)		axa	(0,2)(1,1)(1,2)
diff --git a/src/regexp/testdata/re2-exhaustive.txt.bz2 b/src/regexp/testdata/re2-exhaustive.txt.bz2
new file mode 100644
index 0000000..6638476
--- /dev/null
+++ b/src/regexp/testdata/re2-exhaustive.txt.bz2
diff --git a/src/regexp/testdata/re2-search.txt b/src/regexp/testdata/re2-search.txt
new file mode 100644
index 0000000..8c4098a
--- /dev/null
+++ b/src/regexp/testdata/re2-search.txt
@@ -0,0 +1,3779 @@
+# RE2 basic search tests built by make log
+# Wed May 12 12:13:22 EDT 2021
+Regexp.SearchTests
+strings
+""
+"a"
+regexps
+"a"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a)"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"(?:a)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+strings
+""
+"zyzzyva"
+regexps
+"a"
+-;-;-;-
+-;6-7;-;6-7
+"^(?:a)$"
+-;-;-;-
+-;-;-;-
+"^(?:a)"
+-;-;-;-
+-;-;-;-
+"(?:a)$"
+-;-;-;-
+-;6-7;-;6-7
+strings
+""
+"aa"
+regexps
+"a+"
+-;-;-;-
+0-2;0-2;0-2;0-2
+"^(?:a+)$"
+-;-;-;-
+0-2;0-2;0-2;0-2
+"^(?:a+)"
+-;-;-;-
+0-2;0-2;0-2;0-2
+"(?:a+)$"
+-;-;-;-
+0-2;0-2;0-2;0-2
+strings
+""
+"ab"
+regexps
+"(a+|b)+"
+-;-;-;-
+0-2 1-2;0-2 1-2;0-2 1-2;0-2 1-2
+"^(?:(a+|b)+)$"
+-;-;-;-
+0-2 1-2;0-2 1-2;0-2 1-2;0-2 1-2
+"^(?:(a+|b)+)"
+-;-;-;-
+0-2 1-2;0-2 1-2;0-2 1-2;0-2 1-2
+"(?:(a+|b)+)$"
+-;-;-;-
+0-2 1-2;0-2 1-2;0-2 1-2;0-2 1-2
+strings
+""
+"xabcdx"
+regexps
+"ab|cd"
+-;-;-;-
+-;1-3;-;1-3
+"^(?:ab|cd)$"
+-;-;-;-
+-;-;-;-
+"^(?:ab|cd)"
+-;-;-;-
+-;-;-;-
+"(?:ab|cd)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"hello\ngoodbye\n"
+regexps
+"h.*od?"
+-;-;-;-
+-;0-5;-;0-5
+"^(?:h.*od?)$"
+-;-;-;-
+-;-;-;-
+"^(?:h.*od?)"
+-;-;-;-
+-;0-5;-;0-5
+"(?:h.*od?)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"hello\ngoodbye\n"
+regexps
+"h.*o"
+-;-;-;-
+-;0-5;-;0-5
+"^(?:h.*o)$"
+-;-;-;-
+-;-;-;-
+"^(?:h.*o)"
+-;-;-;-
+-;0-5;-;0-5
+"(?:h.*o)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"goodbye\nhello\n"
+regexps
+"h.*o"
+-;-;-;-
+-;8-13;-;8-13
+"^(?:h.*o)$"
+-;-;-;-
+-;-;-;-
+"^(?:h.*o)"
+-;-;-;-
+-;-;-;-
+"(?:h.*o)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"hello world"
+regexps
+"h.*o"
+-;-;-;-
+-;0-8;-;0-8
+"^(?:h.*o)$"
+-;-;-;-
+-;-;-;-
+"^(?:h.*o)"
+-;-;-;-
+-;0-8;-;0-8
+"(?:h.*o)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"othello, world"
+regexps
+"h.*o"
+-;-;-;-
+-;2-11;-;2-11
+"^(?:h.*o)$"
+-;-;-;-
+-;-;-;-
+"^(?:h.*o)"
+-;-;-;-
+-;-;-;-
+"(?:h.*o)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"aaaaaaa"
+regexps
+"[^\\s\\S]"
+-;-;-;-
+-;-;-;-
+"^(?:[^\\s\\S])$"
+-;-;-;-
+-;-;-;-
+"^(?:[^\\s\\S])"
+-;-;-;-
+-;-;-;-
+"(?:[^\\s\\S])$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"aaaaaaa"
+regexps
+"a"
+-;-;-;-
+-;0-1;-;0-1
+"^(?:a)$"
+-;-;-;-
+-;-;-;-
+"^(?:a)"
+-;-;-;-
+-;0-1;-;0-1
+"(?:a)$"
+-;-;-;-
+-;6-7;-;6-7
+strings
+""
+"aaaaaaa"
+regexps
+"a*"
+0-0;0-0;0-0;0-0
+0-7;0-7;0-7;0-7
+"^(?:a*)$"
+0-0;0-0;0-0;0-0
+0-7;0-7;0-7;0-7
+"^(?:a*)"
+0-0;0-0;0-0;0-0
+0-7;0-7;0-7;0-7
+"(?:a*)$"
+0-0;0-0;0-0;0-0
+0-7;0-7;0-7;0-7
+strings
+""
+""
+regexps
+"a*"
+0-0;0-0;0-0;0-0
+0-0;0-0;0-0;0-0
+"^(?:a*)$"
+0-0;0-0;0-0;0-0
+0-0;0-0;0-0;0-0
+"^(?:a*)"
+0-0;0-0;0-0;0-0
+0-0;0-0;0-0;0-0
+"(?:a*)$"
+0-0;0-0;0-0;0-0
+0-0;0-0;0-0;0-0
+strings
+""
+"xabcdx"
+regexps
+"ab|cd"
+-;-;-;-
+-;1-3;-;1-3
+"^(?:ab|cd)$"
+-;-;-;-
+-;-;-;-
+"^(?:ab|cd)"
+-;-;-;-
+-;-;-;-
+"(?:ab|cd)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"cab"
+regexps
+"a"
+-;-;-;-
+-;1-2;-;1-2
+"^(?:a)$"
+-;-;-;-
+-;-;-;-
+"^(?:a)"
+-;-;-;-
+-;-;-;-
+"(?:a)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"cab"
+regexps
+"a*b"
+-;-;-;-
+-;1-3;-;1-3
+"^(?:a*b)$"
+-;-;-;-
+-;-;-;-
+"^(?:a*b)"
+-;-;-;-
+-;-;-;-
+"(?:a*b)$"
+-;-;-;-
+-;1-3;-;1-3
+strings
+""
+"x"
+regexps
+"((((((((((((((((((((x))))))))))))))))))))"
+-;-;-;-
+0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1
+"^(?:((((((((((((((((((((x)))))))))))))))))))))$"
+-;-;-;-
+0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1
+"^(?:((((((((((((((((((((x)))))))))))))))))))))"
+-;-;-;-
+0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1
+"(?:((((((((((((((((((((x)))))))))))))))))))))$"
+-;-;-;-
+0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1;0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1 0-1
+strings
+""
+"xxxabcdxxx"
+regexps
+"[abcd]"
+-;-;-;-
+-;3-4;-;3-4
+"^(?:[abcd])$"
+-;-;-;-
+-;-;-;-
+"^(?:[abcd])"
+-;-;-;-
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+-;-;-;-
+"(?:(?m)d[ex][fy]$)$"
+-;-;-;-
+-;3-6;-;3-6
+strings
+""
+"abcdeff"
+regexps
+"(?m)d[ex][fy]$"
+-;-;-;-
+-;-;-;-
+"^(?:(?m)d[ex][fy]$)$"
+-;-;-;-
+-;-;-;-
+"^(?:(?m)d[ex][fy]$)"
+-;-;-;-
+-;-;-;-
+"(?:(?m)d[ex][fy]$)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"abcdef"
+regexps
+"(?m)[dz][ex][fy]$"
+-;-;-;-
+-;3-6;-;3-6
+"^(?:(?m)[dz][ex][fy]$)$"
+-;-;-;-
+-;-;-;-
+"^(?:(?m)[dz][ex][fy]$)"
+-;-;-;-
+-;-;-;-
+"(?:(?m)[dz][ex][fy]$)$"
+-;-;-;-
+-;3-6;-;3-6
+strings
+""
+"abcdeff"
+regexps
+"(?m)[dz][ex][fy]$"
+-;-;-;-
+-;-;-;-
+"^(?:(?m)[dz][ex][fy]$)$"
+-;-;-;-
+-;-;-;-
+"^(?:(?m)[dz][ex][fy]$)"
+-;-;-;-
+-;-;-;-
+"(?:(?m)[dz][ex][fy]$)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"a"
+regexps
+"^"
+0-0;0-0;0-0;0-0
+-;0-0;-;0-0
+"^(?:^)$"
+0-0;0-0;0-0;0-0
+-;-;-;-
+"^(?:^)"
+0-0;0-0;0-0;0-0
+-;0-0;-;0-0
+"(?:^)$"
+0-0;0-0;0-0;0-0
+-;-;-;-
+strings
+""
+"a"
+regexps
+"^^"
+0-0;0-0;0-0;0-0
+-;0-0;-;0-0
+"^(?:^^)$"
+0-0;0-0;0-0;0-0
+-;-;-;-
+"^(?:^^)"
+0-0;0-0;0-0;0-0
+-;0-0;-;0-0
+"(?:^^)$"
+0-0;0-0;0-0;0-0
+-;-;-;-
+strings
+""
+"a"
+regexps
+"a"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a)"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"(?:a)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+strings
+""
+"a"
+regexps
+"ab*"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:ab*)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:ab*)"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"(?:ab*)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+strings
+""
+"a"
+regexps
+"a\\C*"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a\\C*)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a\\C*)"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"(?:a\\C*)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+strings
+""
+"a"
+regexps
+"a\\C+"
+-;-;-;-
+-;-;-;-
+"^(?:a\\C+)$"
+-;-;-;-
+-;-;-;-
+"^(?:a\\C+)"
+-;-;-;-
+-;-;-;-
+"(?:a\\C+)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"a"
+regexps
+"a\\C?"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a\\C?)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a\\C?)"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"(?:a\\C?)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+strings
+""
+"a"
+regexps
+"a\\C*?"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a\\C*?)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a\\C*?)"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"(?:a\\C*?)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+strings
+""
+"a"
+regexps
+"a\\C+?"
+-;-;-;-
+-;-;-;-
+"^(?:a\\C+?)$"
+-;-;-;-
+-;-;-;-
+"^(?:a\\C+?)"
+-;-;-;-
+-;-;-;-
+"(?:a\\C+?)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"a"
+regexps
+"a\\C??"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a\\C??)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"^(?:a\\C??)"
+-;-;-;-
+0-1;0-1;0-1;0-1
+"(?:a\\C??)$"
+-;-;-;-
+0-1;0-1;0-1;0-1
+strings
+""
+"baba"
+regexps
+"a\\C*|ba\\C"
+-;-;-;-
+-;0-3;-;0-3
+"^(?:a\\C*|ba\\C)$"
+-;-;-;-
+-;-;-;-
+"^(?:a\\C*|ba\\C)"
+-;-;-;-
+-;0-3;-;0-3
+"(?:a\\C*|ba\\C)$"
+-;-;-;-
+-;1-4;-;1-4
+strings
+""
+"Inc."
+regexps
+"\\w*I\\w*"
+-;-;-;-
+-;0-3;-;0-3
+"^(?:\\w*I\\w*)$"
+-;-;-;-
+-;-;-;-
+"^(?:\\w*I\\w*)"
+-;-;-;-
+-;0-3;-;0-3
+"(?:\\w*I\\w*)$"
+-;-;-;-
+-;-;-;-
+strings
+""
+"aaa"
+regexps
+"(?:|a)*"
+0-0;0-0;0-0;0-0
+0-3;0-0;0-3;0-3
+"^(?:(?:|a)*)$"
+0-0;0-0;0-0;0-0
+0-3;0-3;0-3;0-3
+"^(?:(?:|a)*)"
+0-0;0-0;0-0;0-0
+0-3;0-0;0-3;0-3
+"(?:(?:|a)*)$"
+0-0;0-0;0-0;0-0
+0-3;0-3;0-3;0-3
+strings
+""
+"aaa"
+regexps
+"(?:|a)+"
+0-0;0-0;0-0;0-0
+0-3;0-0;0-3;0-3
+"^(?:(?:|a)+)$"
+0-0;0-0;0-0;0-0
+0-3;0-3;0-3;0-3
+"^(?:(?:|a)+)"
+0-0;0-0;0-0;0-0
+0-3;0-0;0-3;0-3
+"(?:(?:|a)+)$"
+0-0;0-0;0-0;0-0
+0-3;0-3;0-3;0-3
diff --git a/src/regexp/testdata/repetition.dat b/src/regexp/testdata/repetition.dat
new file mode 100644
index 0000000..e6361f5
--- /dev/null
+++ b/src/regexp/testdata/repetition.dat
@@ -0,0 +1,163 @@
+NOTE	implicit vs. explicit repetitions : 2009-02-02
+
+# Glenn Fowler <gsf@research.att.com>
+# conforming matches (column 4) must match one of the following BREs
+#	NOMATCH
+#	(0,.)\((\(.\),\(.\))(?,?)(\2,\3)\)*
+#	(0,.)\((\(.\),\(.\))(\2,\3)(?,?)\)*
+# i.e., each 3-tuple has two identical elements and one (?,?)
+
+E	((..)|(.))				NULL		NOMATCH
+E	((..)|(.))((..)|(.))			NULL		NOMATCH
+E	((..)|(.))((..)|(.))((..)|(.))		NULL		NOMATCH
+
+E	((..)|(.)){1}				NULL		NOMATCH
+E	((..)|(.)){2}				NULL		NOMATCH
+E	((..)|(.)){3}				NULL		NOMATCH
+
+E	((..)|(.))*				NULL		(0,0)
+
+E	((..)|(.))				a		(0,1)(0,1)(?,?)(0,1)
+E	((..)|(.))((..)|(.))			a		NOMATCH
+E	((..)|(.))((..)|(.))((..)|(.))		a		NOMATCH
+
+E	((..)|(.)){1}				a		(0,1)(0,1)(?,?)(0,1)
+E	((..)|(.)){2}				a		NOMATCH
+E	((..)|(.)){3}				a		NOMATCH
+
+E	((..)|(.))*				a		(0,1)(0,1)(?,?)(0,1)
+
+E	((..)|(.))				aa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.))((..)|(.))			aa		(0,2)(0,1)(?,?)(0,1)(1,2)(?,?)(1,2)
+E	((..)|(.))((..)|(.))((..)|(.))		aa		NOMATCH
+
+E	((..)|(.)){1}				aa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.)){2}				aa		(0,2)(1,2)(?,?)(1,2)
+E	((..)|(.)){3}				aa		NOMATCH
+
+E	((..)|(.))*				aa		(0,2)(0,2)(0,2)(?,?)
+
+E	((..)|(.))				aaa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.))((..)|(.))			aaa		(0,3)(0,2)(0,2)(?,?)(2,3)(?,?)(2,3)
+E	((..)|(.))((..)|(.))((..)|(.))		aaa		(0,3)(0,1)(?,?)(0,1)(1,2)(?,?)(1,2)(2,3)(?,?)(2,3)
+
+E	((..)|(.)){1}				aaa		(0,2)(0,2)(0,2)(?,?)
+#E	((..)|(.)){2}				aaa		(0,3)(2,3)(?,?)(2,3)
+E	((..)|(.)){2}				aaa		(0,3)(2,3)(0,2)(2,3)	RE2/Go
+E	((..)|(.)){3}				aaa		(0,3)(2,3)(?,?)(2,3)
+
+#E	((..)|(.))*				aaa		(0,3)(2,3)(?,?)(2,3)
+E	((..)|(.))*				aaa		(0,3)(2,3)(0,2)(2,3)	RE2/Go
+
+E	((..)|(.))				aaaa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.))((..)|(.))			aaaa		(0,4)(0,2)(0,2)(?,?)(2,4)(2,4)(?,?)
+E	((..)|(.))((..)|(.))((..)|(.))		aaaa		(0,4)(0,2)(0,2)(?,?)(2,3)(?,?)(2,3)(3,4)(?,?)(3,4)
+
+E	((..)|(.)){1}				aaaa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.)){2}				aaaa		(0,4)(2,4)(2,4)(?,?)
+#E	((..)|(.)){3}				aaaa		(0,4)(3,4)(?,?)(3,4)
+E	((..)|(.)){3}				aaaa		(0,4)(3,4)(0,2)(3,4)	RE2/Go
+
+E	((..)|(.))*				aaaa		(0,4)(2,4)(2,4)(?,?)
+
+E	((..)|(.))				aaaaa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.))((..)|(.))			aaaaa		(0,4)(0,2)(0,2)(?,?)(2,4)(2,4)(?,?)
+E	((..)|(.))((..)|(.))((..)|(.))		aaaaa		(0,5)(0,2)(0,2)(?,?)(2,4)(2,4)(?,?)(4,5)(?,?)(4,5)
+
+E	((..)|(.)){1}				aaaaa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.)){2}				aaaaa		(0,4)(2,4)(2,4)(?,?)
+#E	((..)|(.)){3}				aaaaa		(0,5)(4,5)(?,?)(4,5)
+E	((..)|(.)){3}				aaaaa		(0,5)(4,5)(2,4)(4,5)	RE2/Go
+
+#E	((..)|(.))*				aaaaa		(0,5)(4,5)(?,?)(4,5)
+E	((..)|(.))*				aaaaa		(0,5)(4,5)(2,4)(4,5)	RE2/Go
+
+E	((..)|(.))				aaaaaa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.))((..)|(.))			aaaaaa		(0,4)(0,2)(0,2)(?,?)(2,4)(2,4)(?,?)
+E	((..)|(.))((..)|(.))((..)|(.))		aaaaaa		(0,6)(0,2)(0,2)(?,?)(2,4)(2,4)(?,?)(4,6)(4,6)(?,?)
+
+E	((..)|(.)){1}				aaaaaa		(0,2)(0,2)(0,2)(?,?)
+E	((..)|(.)){2}				aaaaaa		(0,4)(2,4)(2,4)(?,?)
+E	((..)|(.)){3}				aaaaaa		(0,6)(4,6)(4,6)(?,?)
+
+E	((..)|(.))*				aaaaaa		(0,6)(4,6)(4,6)(?,?)
+
+NOTE	additional repetition tests graciously provided by Chris Kuklewicz www.haskell.org 2009-02-02
+
+# These test a bug in OS X / FreeBSD / NetBSD, and libtree. 
+# Linux/GLIBC gets the {8,} and {8,8} wrong.
+
+:HA#100:E	X(.?){0,}Y	X1234567Y	(0,9)(7,8)
+:HA#101:E	X(.?){1,}Y	X1234567Y	(0,9)(7,8)
+:HA#102:E	X(.?){2,}Y	X1234567Y	(0,9)(7,8)
+:HA#103:E	X(.?){3,}Y	X1234567Y	(0,9)(7,8)
+:HA#104:E	X(.?){4,}Y	X1234567Y	(0,9)(7,8)
+:HA#105:E	X(.?){5,}Y	X1234567Y	(0,9)(7,8)
+:HA#106:E	X(.?){6,}Y	X1234567Y	(0,9)(7,8)
+:HA#107:E	X(.?){7,}Y	X1234567Y	(0,9)(7,8)
+:HA#108:E	X(.?){8,}Y	X1234567Y	(0,9)(8,8)
+#:HA#110:E	X(.?){0,8}Y	X1234567Y	(0,9)(7,8)
+:HA#110:E	X(.?){0,8}Y	X1234567Y	(0,9)(8,8)	RE2/Go
+#:HA#111:E	X(.?){1,8}Y	X1234567Y	(0,9)(7,8)
+:HA#111:E	X(.?){1,8}Y	X1234567Y	(0,9)(8,8)	RE2/Go
+#:HA#112:E	X(.?){2,8}Y	X1234567Y	(0,9)(7,8)
+:HA#112:E	X(.?){2,8}Y	X1234567Y	(0,9)(8,8)	RE2/Go
+#:HA#113:E	X(.?){3,8}Y	X1234567Y	(0,9)(7,8)
+:HA#113:E	X(.?){3,8}Y	X1234567Y	(0,9)(8,8)	RE2/Go
+#:HA#114:E	X(.?){4,8}Y	X1234567Y	(0,9)(7,8)
+:HA#114:E	X(.?){4,8}Y	X1234567Y	(0,9)(8,8)	RE2/Go
+#:HA#115:E	X(.?){5,8}Y	X1234567Y	(0,9)(7,8)
+:HA#115:E	X(.?){5,8}Y	X1234567Y	(0,9)(8,8)	RE2/Go
+#:HA#116:E	X(.?){6,8}Y	X1234567Y	(0,9)(7,8)
+:HA#116:E	X(.?){6,8}Y	X1234567Y	(0,9)(8,8)	RE2/Go
+#:HA#117:E	X(.?){7,8}Y	X1234567Y	(0,9)(7,8)
+:HA#117:E	X(.?){7,8}Y	X1234567Y	(0,9)(8,8)	RE2/Go
+:HA#118:E	X(.?){8,8}Y	X1234567Y	(0,9)(8,8)
+
+# These test a fixed bug in my regex-tdfa that did not keep the expanded
+# form properly grouped, so right association did the wrong thing with
+# these ambiguous patterns (crafted just to test my code when I became
+# suspicious of my implementation).  The first subexpression should use
+# "ab" then "a" then "bcd".
+
+# OS X / FreeBSD / NetBSD badly fail many of these, with impossible
+# results like (0,6)(4,5)(6,6).
+
+:HA#260:E	(a|ab|c|bcd){0,}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#261:E	(a|ab|c|bcd){1,}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#262:E	(a|ab|c|bcd){2,}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#263:E	(a|ab|c|bcd){3,}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#264:E	(a|ab|c|bcd){4,}(d*)	ababcd	NOMATCH
+:HA#265:E	(a|ab|c|bcd){0,10}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#266:E	(a|ab|c|bcd){1,10}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#267:E	(a|ab|c|bcd){2,10}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#268:E	(a|ab|c|bcd){3,10}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#269:E	(a|ab|c|bcd){4,10}(d*)	ababcd	NOMATCH
+:HA#270:E	(a|ab|c|bcd)*(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#271:E	(a|ab|c|bcd)+(d*)	ababcd	(0,6)(3,6)(6,6)
+
+# The above worked on Linux/GLIBC but the following often fail.
+# They also trip up OS X / FreeBSD / NetBSD:
+
+#:HA#280:E	(ab|a|c|bcd){0,}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#280:E	(ab|a|c|bcd){0,}(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+#:HA#281:E	(ab|a|c|bcd){1,}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#281:E	(ab|a|c|bcd){1,}(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+#:HA#282:E	(ab|a|c|bcd){2,}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#282:E	(ab|a|c|bcd){2,}(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+#:HA#283:E	(ab|a|c|bcd){3,}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#283:E	(ab|a|c|bcd){3,}(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+:HA#284:E	(ab|a|c|bcd){4,}(d*)	ababcd	NOMATCH
+#:HA#285:E	(ab|a|c|bcd){0,10}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#285:E	(ab|a|c|bcd){0,10}(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+#:HA#286:E	(ab|a|c|bcd){1,10}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#286:E	(ab|a|c|bcd){1,10}(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+#:HA#287:E	(ab|a|c|bcd){2,10}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#287:E	(ab|a|c|bcd){2,10}(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+#:HA#288:E	(ab|a|c|bcd){3,10}(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#288:E	(ab|a|c|bcd){3,10}(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+:HA#289:E	(ab|a|c|bcd){4,10}(d*)	ababcd	NOMATCH
+#:HA#290:E	(ab|a|c|bcd)*(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#290:E	(ab|a|c|bcd)*(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
+#:HA#291:E	(ab|a|c|bcd)+(d*)	ababcd	(0,6)(3,6)(6,6)
+:HA#291:E	(ab|a|c|bcd)+(d*)	ababcd	(0,6)(4,5)(5,6)	RE2/Go
diff --git a/src/regexp/testdata/testregex.c b/src/regexp/testdata/testregex.c
new file mode 100644
index 0000000..37545d0
--- /dev/null
+++ b/src/regexp/testdata/testregex.c
@@ -0,0 +1,2286 @@
+#pragma prototyped noticed
+
+/*
+ * regex(3) test harness
+ *
+ * build:	cc -o testregex testregex.c
+ * help:	testregex --man
+ * note:	REG_* features are detected by #ifdef; if REG_* are enums
+ *		then supply #define REG_foo REG_foo for each enum REG_foo
+ *
+ *	Glenn Fowler <gsf@research.att.com>
+ *	AT&T Research
+ *
+ * PLEASE: publish your tests so everyone can benefit
+ *
+ * The following license covers testregex.c and all associated test data.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of THIS SOFTWARE FILE (the "Software"), to deal in the Software
+ * without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do
+ * so, subject to the following disclaimer:
+ *
+ * THIS SOFTWARE IS PROVIDED BY AT&T ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
+ * IN NO EVENT SHALL AT&T BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+static const char id[] = "\n@(#)$Id: testregex (AT&T Research) 2010-06-10 $\0\n";
+
+#if _PACKAGE_ast
+#include <ast.h>
+#else
+#include <sys/types.h>
+#endif
+
+#include <stdio.h>
+#include <regex.h>
+#include <ctype.h>
+#include <setjmp.h>
+#include <signal.h>
+#include <string.h>
+#include <unistd.h>
+
+#ifdef	__STDC__
+#include <stdlib.h>
+#include <locale.h>
+#endif
+
+#ifndef RE_DUP_MAX
+#define RE_DUP_MAX	32767
+#endif
+
+#if !_PACKAGE_ast
+#undef	REG_DISCIPLINE
+#endif
+
+#ifndef REG_DELIMITED
+#undef	_REG_subcomp
+#endif
+
+#define TEST_ARE		0x00000001
+#define TEST_BRE		0x00000002
+#define TEST_ERE		0x00000004
+#define TEST_KRE		0x00000008
+#define TEST_LRE		0x00000010
+#define TEST_SRE		0x00000020
+
+#define TEST_EXPAND		0x00000100
+#define TEST_LENIENT		0x00000200
+
+#define TEST_QUERY		0x00000400
+#define TEST_SUB		0x00000800
+#define TEST_UNSPECIFIED	0x00001000
+#define TEST_VERIFY		0x00002000
+#define TEST_AND		0x00004000
+#define TEST_OR			0x00008000
+
+#define TEST_DELIMIT		0x00010000
+#define TEST_OK			0x00020000
+#define TEST_SAME		0x00040000
+
+#define TEST_ACTUAL		0x00100000
+#define TEST_BASELINE		0x00200000
+#define TEST_FAIL		0x00400000
+#define TEST_PASS		0x00800000
+#define TEST_SUMMARY		0x01000000
+
+#define TEST_IGNORE_ERROR	0x02000000
+#define TEST_IGNORE_OVER	0x04000000
+#define TEST_IGNORE_POSITION	0x08000000
+
+#define TEST_CATCH		0x10000000
+#define TEST_VERBOSE		0x20000000
+
+#define TEST_DECOMP		0x40000000
+
+#define TEST_GLOBAL		(TEST_ACTUAL|TEST_AND|TEST_BASELINE|TEST_CATCH|TEST_FAIL|TEST_IGNORE_ERROR|TEST_IGNORE_OVER|TEST_IGNORE_POSITION|TEST_OR|TEST_PASS|TEST_SUMMARY|TEST_VERBOSE)
+
+#ifdef REG_DISCIPLINE
+
+
+#include <stk.h>
+
+typedef struct Disc_s
+{
+	regdisc_t	disc;
+	int		ordinal;
+	Sfio_t*		sp;
+} Disc_t;
+
+static void*
+compf(const regex_t* re, const char* xstr, size_t xlen, regdisc_t* disc)
+{
+	Disc_t*		dp = (Disc_t*)disc;
+
+	return (void*)((char*)0 + ++dp->ordinal);
+}
+
+static int
+execf(const regex_t* re, void* data, const char* xstr, size_t xlen, const char* sstr, size_t slen, char** snxt, regdisc_t* disc)
+{
+	Disc_t*		dp = (Disc_t*)disc;
+
+	sfprintf(dp->sp, "{%-.*s}(%lu:%d)", xlen, xstr, (char*)data - (char*)0, slen);
+	return atoi(xstr);
+}
+
+static void*
+resizef(void* handle, void* data, size_t size)
+{
+	if (!size)
+		return 0;
+	return stkalloc((Sfio_t*)handle, size);
+}
+
+#endif
+
+#ifndef NiL
+#ifdef	__STDC__
+#define NiL		0
+#else
+#define NiL		(char*)0
+#endif
+#endif
+
+#define H(x)		do{if(html)fprintf(stderr,x);}while(0)
+#define T(x)		fprintf(stderr,x)
+
+static void
+help(int html)
+{
+H("<!DOCTYPE HTML PUBLIC \"-//IETF//DTD HTML//EN\">\n");
+H("<HTML>\n");
+H("<HEAD>\n");
+H("<TITLE>testregex man document</TITLE>\n");
+H("</HEAD>\n");
+H("<BODY bgcolor=white>\n");
+H("<PRE>\n");
+T("NAME\n");
+T("  testregex - regex(3) test harness\n");
+T("\n");
+T("SYNOPSIS\n");
+T("  testregex [ options ]\n");
+T("\n");
+T("DESCRIPTION\n");
+T("  testregex reads regex(3) test specifications, one per line, from the\n");
+T("  standard input and writes one output line for each failed test. A\n");
+T("  summary line is written after all tests are done. Each successful\n");
+T("  test is run again with REG_NOSUB. Unsupported features are noted\n");
+T("  before the first test, and tests requiring these features are\n");
+T("  silently ignored.\n");
+T("\n");
+T("OPTIONS\n");
+T("  -c	catch signals and non-terminating calls\n");
+T("  -e	ignore error return mismatches\n");
+T("  -h	list help on standard error\n");
+T("  -n	do not repeat successful tests with regnexec()\n");
+T("  -o	ignore match[] overrun errors\n");
+T("  -p	ignore negative position mismatches\n");
+T("  -s	use stack instead of malloc\n");
+T("  -x	do not repeat successful tests with REG_NOSUB\n");
+T("  -v	list each test line\n");
+T("  -A	list failed test lines with actual answers\n");
+T("  -B	list all test lines with actual answers\n");
+T("  -F	list failed test lines\n");
+T("  -P	list passed test lines\n");
+T("  -S	output one summary line\n");
+T("\n");
+T("INPUT FORMAT\n");
+T("  Input lines may be blank, a comment beginning with #, or a test\n");
+T("  specification. A specification is five fields separated by one\n");
+T("  or more tabs. NULL denotes the empty string and NIL denotes the\n");
+T("  0 pointer.\n");
+T("\n");
+T("  Field 1: the regex(3) flags to apply, one character per REG_feature\n");
+T("  flag. The test is skipped if REG_feature is not supported by the\n");
+T("  implementation. If the first character is not [BEASKLP] then the\n");
+T("  specification is a global control line. One or more of [BEASKLP] may be\n");
+T("  specified; the test will be repeated for each mode.\n");
+T("\n");
+T("    B 	basic			BRE	(grep, ed, sed)\n");
+T("    E 	REG_EXTENDED		ERE	(egrep)\n");
+T("    A	REG_AUGMENTED		ARE	(egrep with negation)\n");
+T("    S	REG_SHELL		SRE	(sh glob)\n");
+T("    K	REG_SHELL|REG_AUGMENTED	KRE	(ksh glob)\n");
+T("    L	REG_LITERAL		LRE	(fgrep)\n");
+T("\n");
+T("    a	REG_LEFT|REG_RIGHT	implicit ^...$\n");
+T("    b	REG_NOTBOL		lhs does not match ^\n");
+T("    c	REG_COMMENT		ignore space and #...\\n\n");
+T("    d	REG_SHELL_DOT		explicit leading . match\n");
+T("    e	REG_NOTEOL		rhs does not match $\n");
+T("    f	REG_MULTIPLE		multiple \\n separated patterns\n");
+T("    g	FNM_LEADING_DIR		testfnmatch only -- match until /\n");
+T("    h	REG_MULTIREF		multiple digit backref\n");
+T("    i	REG_ICASE		ignore case\n");
+T("    j	REG_SPAN		. matches \\n\n");
+T("    k	REG_ESCAPE		\\ to ecape [...] delimiter\n");
+T("    l	REG_LEFT		implicit ^...\n");
+T("    m	REG_MINIMAL		minimal match\n");
+T("    n	REG_NEWLINE		explicit \\n match\n");
+T("    o	REG_ENCLOSED		(|&) magic inside [@|&](...)\n");
+T("    p	REG_SHELL_PATH		explicit / match\n");
+T("    q	REG_DELIMITED		delimited pattern\n");
+T("    r	REG_RIGHT		implicit ...$\n");
+T("    s	REG_SHELL_ESCAPED	\\ not special\n");
+T("    t	REG_MUSTDELIM		all delimiters must be specified\n");
+T("    u	standard unspecified behavior -- errors not counted\n");
+T("    v	REG_CLASS_ESCAPE	\\ special inside [...]\n");
+T("    w	REG_NOSUB		no subexpression match array\n");
+T("    x	REG_LENIENT		let some errors slide\n");
+T("    y	REG_LEFT		regexec() implicit ^...\n");
+T("    z	REG_NULL		NULL subexpressions ok\n");
+T("    $	                        expand C \\c escapes in fields 2 and 3\n");
+T("    /	                        field 2 is a regsubcomp() expression\n");
+T("    =	                        field 3 is a regdecomp() expression\n");
+T("\n");
+T("  Field 1 control lines:\n");
+T("\n");
+T("    C		set LC_COLLATE and LC_CTYPE to locale in field 2\n");
+T("\n");
+T("    ?test ...	output field 5 if passed and != EXPECTED, silent otherwise\n");
+T("    &test ...	output field 5 if current and previous passed\n");
+T("    |test ...	output field 5 if current passed and previous failed\n");
+T("    ; ...	output field 2 if previous failed\n");
+T("    {test ...	skip if failed until }\n");
+T("    }		end of skip\n");
+T("\n");
+T("    : comment		comment copied as output NOTE\n");
+T("    :comment:test	:comment: ignored\n");
+T("    N[OTE] comment	comment copied as output NOTE\n");
+T("    T[EST] comment	comment\n");
+T("\n");
+T("    number		use number for nmatch (20 by default)\n");
+T("\n");
+T("  Field 2: the regular expression pattern; SAME uses the pattern from\n");
+T("    the previous specification. RE_DUP_MAX inside {...} expands to the\n");
+T("    value from <limits.h>.\n");
+T("\n");
+T("  Field 3: the string to match. X...{RE_DUP_MAX} expands to RE_DUP_MAX\n");
+T("    copies of X.\n");
+T("\n");
+T("  Field 4: the test outcome. This is either one of the posix error\n");
+T("    codes (with REG_ omitted) or the match array, a list of (m,n)\n");
+T("    entries with m and n being first and last+1 positions in the\n");
+T("    field 3 string, or NULL if REG_NOSUB is in effect and success\n");
+T("    is expected. BADPAT is acceptable in place of any regcomp(3)\n");
+T("    error code. The match[] array is initialized to (-2,-2) before\n");
+T("    each test. All array elements from 0 to nmatch-1 must be specified\n");
+T("    in the outcome. Unspecified endpoints (offset -1) are denoted by ?.\n");
+T("    Unset endpoints (offset -2) are denoted by X. {x}(o:n) denotes a\n");
+T("    matched (?{...}) expression, where x is the text enclosed by {...},\n");
+T("    o is the expression ordinal counting from 1, and n is the length of\n");
+T("    the unmatched portion of the subject string. If x starts with a\n");
+T("    number then that is the return value of re_execf(), otherwise 0 is\n");
+T("    returned. RE_DUP_MAX[-+]N expands to the <limits.h> value -+N.\n");
+T("\n");
+T("  Field 5: optional comment appended to the report.\n");
+T("\n");
+T("CAVEAT\n");
+T("    If a regex implementation misbehaves with memory then all bets are off.\n");
+T("\n");
+T("CONTRIBUTORS\n");
+T("  Glenn Fowler    gsf@research.att.com        (ksh strmatch, regex extensions)\n");
+T("  David Korn      dgk@research.att.com        (ksh glob matcher)\n");
+T("  Doug McIlroy    mcilroy@dartmouth.edu       (ast regex/testre in C++)\n");
+T("  Tom Lord        lord@regexps.com            (rx tests)\n");
+T("  Henry Spencer   henry@zoo.toronto.edu       (original public regex)\n");
+T("  Andrew Hume     andrew@research.att.com     (gre tests)\n");
+T("  John Maddock    John_Maddock@compuserve.com (regex++ tests)\n");
+T("  Philip Hazel    ph10@cam.ac.uk              (pcre tests)\n");
+T("  Ville Laurikari vl@iki.fi                   (libtre tests)\n");
+H("</PRE>\n");
+H("</BODY>\n");
+H("</HTML>\n");
+}
+
+#ifndef elementsof
+#define elementsof(x)	(sizeof(x)/sizeof(x[0]))
+#endif
+
+#ifndef streq
+#define streq(a,b)	(*(a)==*(b)&&!strcmp(a,b))
+#endif
+
+#define HUNG		2
+#define NOTEST		(~0)
+
+#ifndef REG_TEST_DEFAULT
+#define REG_TEST_DEFAULT	0
+#endif
+
+#ifndef REG_EXEC_DEFAULT
+#define REG_EXEC_DEFAULT	0
+#endif
+
+static const char* unsupported[] =
+{
+	"BASIC",
+#ifndef REG_EXTENDED
+	"EXTENDED",
+#endif
+#ifndef REG_AUGMENTED
+	"AUGMENTED",
+#endif
+#ifndef REG_SHELL
+	"SHELL",
+#endif
+
+#ifndef REG_CLASS_ESCAPE
+	"CLASS_ESCAPE",
+#endif
+#ifndef REG_COMMENT
+	"COMMENT",
+#endif
+#ifndef REG_DELIMITED
+	"DELIMITED",
+#endif
+#ifndef REG_DISCIPLINE
+	"DISCIPLINE",
+#endif
+#ifndef REG_ESCAPE
+	"ESCAPE",
+#endif
+#ifndef REG_ICASE
+	"ICASE",
+#endif
+#ifndef REG_LEFT
+	"LEFT",
+#endif
+#ifndef REG_LENIENT
+	"LENIENT",
+#endif
+#ifndef REG_LITERAL
+	"LITERAL",
+#endif
+#ifndef REG_MINIMAL
+	"MINIMAL",
+#endif
+#ifndef REG_MULTIPLE
+	"MULTIPLE",
+#endif
+#ifndef REG_MULTIREF
+	"MULTIREF",
+#endif
+#ifndef REG_MUSTDELIM
+	"MUSTDELIM",
+#endif
+#ifndef REG_NEWLINE
+	"NEWLINE",
+#endif
+#ifndef REG_NOTBOL
+	"NOTBOL",
+#endif
+#ifndef REG_NOTEOL
+	"NOTEOL",
+#endif
+#ifndef REG_NULL
+	"NULL",
+#endif
+#ifndef REG_RIGHT
+	"RIGHT",
+#endif
+#ifndef REG_SHELL_DOT
+	"SHELL_DOT",
+#endif
+#ifndef REG_SHELL_ESCAPED
+	"SHELL_ESCAPED",
+#endif
+#ifndef REG_SHELL_GROUP
+	"SHELL_GROUP",
+#endif
+#ifndef REG_SHELL_PATH
+	"SHELL_PATH",
+#endif
+#ifndef REG_SPAN
+	"SPAN",
+#endif
+#if REG_NOSUB & REG_TEST_DEFAULT
+	"SUBMATCH",
+#endif
+#if !_REG_nexec
+	"regnexec",
+#endif
+#if !_REG_subcomp
+	"regsubcomp",
+#endif
+#if !_REG_decomp
+	"redecomp",
+#endif
+	0
+};
+
+#ifndef REG_CLASS_ESCAPE
+#define REG_CLASS_ESCAPE	NOTEST
+#endif
+#ifndef REG_COMMENT
+#define REG_COMMENT	NOTEST
+#endif
+#ifndef REG_DELIMITED
+#define REG_DELIMITED	NOTEST
+#endif
+#ifndef REG_ESCAPE
+#define REG_ESCAPE	NOTEST
+#endif
+#ifndef REG_ICASE
+#define REG_ICASE	NOTEST
+#endif
+#ifndef REG_LEFT
+#define REG_LEFT	NOTEST
+#endif
+#ifndef REG_LENIENT
+#define REG_LENIENT	0
+#endif
+#ifndef REG_MINIMAL
+#define REG_MINIMAL	NOTEST
+#endif
+#ifndef REG_MULTIPLE
+#define REG_MULTIPLE	NOTEST
+#endif
+#ifndef REG_MULTIREF
+#define REG_MULTIREF	NOTEST
+#endif
+#ifndef REG_MUSTDELIM
+#define REG_MUSTDELIM	NOTEST
+#endif
+#ifndef REG_NEWLINE
+#define REG_NEWLINE	NOTEST
+#endif
+#ifndef REG_NOTBOL
+#define REG_NOTBOL	NOTEST
+#endif
+#ifndef REG_NOTEOL
+#define REG_NOTEOL	NOTEST
+#endif
+#ifndef REG_NULL
+#define REG_NULL	NOTEST
+#endif
+#ifndef REG_RIGHT
+#define REG_RIGHT	NOTEST
+#endif
+#ifndef REG_SHELL_DOT
+#define REG_SHELL_DOT	NOTEST
+#endif
+#ifndef REG_SHELL_ESCAPED
+#define REG_SHELL_ESCAPED	NOTEST
+#endif
+#ifndef REG_SHELL_GROUP
+#define REG_SHELL_GROUP	NOTEST
+#endif
+#ifndef REG_SHELL_PATH
+#define REG_SHELL_PATH	NOTEST
+#endif
+#ifndef REG_SPAN
+#define REG_SPAN	NOTEST
+#endif
+
+#define REG_UNKNOWN	(-1)
+
+#ifndef REG_ENEWLINE
+#define REG_ENEWLINE	(REG_UNKNOWN-1)
+#endif
+#ifndef REG_ENULL
+#ifndef REG_EMPTY
+#define REG_ENULL	(REG_UNKNOWN-2)
+#else
+#define REG_ENULL	REG_EMPTY
+#endif
+#endif
+#ifndef REG_ECOUNT
+#define REG_ECOUNT	(REG_UNKNOWN-3)
+#endif
+#ifndef REG_BADESC
+#define REG_BADESC	(REG_UNKNOWN-4)
+#endif
+#ifndef REG_EMEM
+#define REG_EMEM	(REG_UNKNOWN-5)
+#endif
+#ifndef REG_EHUNG
+#define REG_EHUNG	(REG_UNKNOWN-6)
+#endif
+#ifndef REG_EBUS
+#define REG_EBUS	(REG_UNKNOWN-7)
+#endif
+#ifndef REG_EFAULT
+#define REG_EFAULT	(REG_UNKNOWN-8)
+#endif
+#ifndef REG_EFLAGS
+#define REG_EFLAGS	(REG_UNKNOWN-9)
+#endif
+#ifndef REG_EDELIM
+#define REG_EDELIM	(REG_UNKNOWN-9)
+#endif
+
+static const struct { int code; char* name; } codes[] =
+{
+	REG_UNKNOWN,	"UNKNOWN",
+	REG_NOMATCH,	"NOMATCH",
+	REG_BADPAT,	"BADPAT",
+	REG_ECOLLATE,	"ECOLLATE",
+	REG_ECTYPE,	"ECTYPE",
+	REG_EESCAPE,	"EESCAPE",
+	REG_ESUBREG,	"ESUBREG",
+	REG_EBRACK,	"EBRACK",
+	REG_EPAREN,	"EPAREN",
+	REG_EBRACE,	"EBRACE",
+	REG_BADBR,	"BADBR",
+	REG_ERANGE,	"ERANGE",
+	REG_ESPACE,	"ESPACE",
+	REG_BADRPT,	"BADRPT",
+	REG_ENEWLINE,	"ENEWLINE",
+	REG_ENULL,	"ENULL",
+	REG_ECOUNT,	"ECOUNT",
+	REG_BADESC,	"BADESC",
+	REG_EMEM,	"EMEM",
+	REG_EHUNG,	"EHUNG",
+	REG_EBUS,	"EBUS",
+	REG_EFAULT,	"EFAULT",
+	REG_EFLAGS,	"EFLAGS",
+	REG_EDELIM,	"EDELIM",
+};
+
+static struct
+{
+	regmatch_t	NOMATCH;
+	int		errors;
+	int		extracted;
+	int		ignored;
+	int		lineno;
+	int		passed;
+	int		signals;
+	int		unspecified;
+	int		verify;
+	int		warnings;
+	char*		file;
+	char*		stack;
+	char*		which;
+	jmp_buf		gotcha;
+#ifdef REG_DISCIPLINE
+	Disc_t		disc;
+#endif
+} state;
+
+static void
+quote(char* s, int len, unsigned long test)
+{
+	unsigned char*	u = (unsigned char*)s;
+	unsigned char*	e;
+	int		c;
+#ifdef MB_CUR_MAX
+	int		w;
+#endif
+
+	if (!u)
+		printf("NIL");
+	else if (!*u && len <= 1)
+		printf("NULL");
+	else if (test & TEST_EXPAND)
+	{
+		if (len < 0)
+			len = strlen((char*)u);
+		e = u + len;
+		if (test & TEST_DELIMIT)
+			printf("\"");
+		while (u < e)
+			switch (c = *u++)
+			{
+			case '\\':
+				printf("\\\\");
+				break;
+			case '"':
+				if (test & TEST_DELIMIT)
+					printf("\\\"");
+				else
+					printf("\"");
+				break;
+			case '\a':
+				printf("\\a");
+				break;
+			case '\b':
+				printf("\\b");
+				break;
+			case 033:
+				printf("\\e");
+				break;
+			case '\f':
+				printf("\\f");
+				break;
+			case '\n':
+				printf("\\n");
+				break;
+			case '\r':
+				printf("\\r");
+				break;
+			case '\t':
+				printf("\\t");
+				break;
+			case '\v':
+				printf("\\v");
+				break;
+			default:
+#ifdef MB_CUR_MAX
+				s = (char*)u - 1;
+				if ((w = mblen(s, (char*)e - s)) > 1)
+				{
+					u += w - 1;
+					fwrite(s, 1, w, stdout);
+				}
+				else
+#endif
+				if (!iscntrl(c) && isprint(c))
+					putchar(c);
+				else
+					printf("\\x%02x", c);
+				break;
+			}
+		if (test & TEST_DELIMIT)
+			printf("\"");
+	}
+	else
+		printf("%s", s);
+}
+
+static void
+report(char* comment, char* fun, char* re, char* s, int len, char* msg, int flags, unsigned long test)
+{
+	if (state.file)
+		printf("%s:", state.file);
+	printf("%d:", state.lineno);
+	if (re)
+	{
+		printf(" ");
+		quote(re, -1, test|TEST_DELIMIT);
+		if (s)
+		{
+			printf(" versus ");
+			quote(s, len, test|TEST_DELIMIT);
+		}
+	}
+	if (test & TEST_UNSPECIFIED)
+	{
+		state.unspecified++;
+		printf(" unspecified behavior");
+	}
+	else
+		state.errors++;
+	if (state.which)
+		printf(" %s", state.which);
+	if (flags & REG_NOSUB)
+		printf(" NOSUB");
+	if (fun)
+		printf(" %s", fun);
+	if (comment[strlen(comment)-1] == '\n')
+		printf(" %s", comment);
+	else
+	{
+		printf(" %s: ", comment);
+		if (msg)
+			printf("%s: ", msg);
+	}
+}
+
+static void
+error(regex_t* preg, int code)
+{
+	char*	msg;
+	char	buf[256];
+
+	switch (code)
+	{
+	case REG_EBUS:
+		msg = "bus error";
+		break;
+	case REG_EFAULT:
+		msg = "memory fault";
+		break;
+	case REG_EHUNG:
+		msg = "did not terminate";
+		break;
+	default:
+		regerror(code, preg, msg = buf, sizeof buf);
+		break;
+	}
+	printf("%s\n", msg);
+}
+
+static void
+bad(char* comment, char* re, char* s, int len, unsigned long test)
+{
+	printf("bad test case ");
+	report(comment, NiL, re, s, len, NiL, 0, test);
+	exit(1);
+}
+
+static int
+escape(char* s)
+{
+	char*	b;
+	char*	t;
+	char*	q;
+	char*	e;
+	int	c;
+
+	for (b = t = s; *t = *s; s++, t++)
+		if (*s == '\\')
+			switch (*++s)
+			{
+			case '\\':
+				break;
+			case 'a':
+				*t = '\a';
+				break;
+			case 'b':
+				*t = '\b';
+				break;
+			case 'c':
+				if (*t = *++s)
+					*t &= 037;
+				else
+					s--;
+				break;
+			case 'e':
+			case 'E':
+				*t = 033;
+				break;
+			case 'f':
+				*t = '\f';
+				break;
+			case 'n':
+				*t = '\n';
+				break;
+			case 'r':
+				*t = '\r';
+				break;
+			case 's':
+				*t = ' ';
+				break;
+			case 't':
+				*t = '\t';
+				break;
+			case 'v':
+				*t = '\v';
+				break;
+			case 'u':
+			case 'x':
+				c = 0;
+				q = c == 'u' ? (s + 5) : (char*)0;
+				e = s + 1;
+				while (!e || !q || s < q)
+				{
+					switch (*++s)
+					{
+					case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
+						c = (c << 4) + *s - 'a' + 10;
+						continue;
+					case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
+						c = (c << 4) + *s - 'A' + 10;
+						continue;
+					case '0': case '1': case '2': case '3': case '4':
+					case '5': case '6': case '7': case '8': case '9':
+						c = (c << 4) + *s - '0';
+						continue;
+					case '{':
+					case '[':
+						if (s != e)
+						{
+							s--;
+							break;
+						}
+						e = 0;
+						continue;
+					case '}':
+					case ']':
+						if (e)
+							s--;
+						break;
+					default:
+						s--;
+						break;
+					}
+					break;
+				}
+				*t = c;
+				break;
+			case '0': case '1': case '2': case '3':
+			case '4': case '5': case '6': case '7':
+				c = *s - '0';
+				q = s + 2;
+				while (s < q)
+				{
+					switch (*++s)
+					{
+					case '0': case '1': case '2': case '3':
+					case '4': case '5': case '6': case '7':
+						c = (c << 3) + *s - '0';
+						break;
+					default:
+						q = --s;
+						break;
+					}
+				}
+				*t = c;
+				break;
+			default:
+				*(s + 1) = 0;
+				bad("invalid C \\ escape\n", s - 1, NiL, 0, 0);
+			}
+	return t - b;
+}
+
+static void
+matchoffprint(int off)
+{
+	switch (off)
+	{
+	case -2:
+		printf("X");
+		break;
+	case -1:
+		printf("?");
+		break;
+	default:
+		printf("%d", off);
+		break;
+	}
+}
+
+static void
+matchprint(regmatch_t* match, int nmatch, int nsub, char* ans, unsigned long test)
+{
+	int	i;
+
+	for (; nmatch > nsub + 1; nmatch--)
+		if ((match[nmatch-1].rm_so != -1 || match[nmatch-1].rm_eo != -1) && (!(test & TEST_IGNORE_POSITION) || match[nmatch-1].rm_so >= 0 && match[nmatch-1].rm_eo >= 0))
+			break;
+	for (i = 0; i < nmatch; i++)
+	{
+		printf("(");
+		matchoffprint(match[i].rm_so);
+		printf(",");
+		matchoffprint(match[i].rm_eo);
+		printf(")");
+	}
+	if (!(test & (TEST_ACTUAL|TEST_BASELINE)))
+	{
+		if (ans)
+			printf(" expected: %s", ans);
+		printf("\n");
+	}
+}
+
+static int
+matchcheck(regmatch_t* match, int nmatch, int nsub, char* ans, char* re, char* s, int len, int flags, unsigned long test)
+{
+	char*	p;
+	int	i;
+	int	m;
+	int	n;
+
+	if (streq(ans, "OK"))
+		return test & (TEST_BASELINE|TEST_PASS|TEST_VERIFY);
+	for (i = 0, p = ans; i < nmatch && *p; i++)
+	{
+		if (*p == '{')
+		{
+#ifdef REG_DISCIPLINE
+			char*	x;
+
+			if (!(x = sfstruse(state.disc.sp)))
+				bad("out of space [discipline string]\n", NiL, NiL, 0, 0);
+			if (strcmp(p, x))
+			{
+				if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+					return 0;
+				report("callout failed", NiL, re, s, len, NiL, flags, test);
+				quote(p, -1, test);
+				printf(" expected, ");
+				quote(x, -1, test);
+				printf(" returned\n");
+			}
+#endif
+			break;
+		}
+		if (*p++ != '(')
+			bad("improper answer\n", re, s, -1, test);
+		if (*p == '?')
+		{
+			m = -1;
+			p++;
+		}
+		else if (*p == 'R' && !memcmp(p, "RE_DUP_MAX", 10))
+		{
+			m = RE_DUP_MAX;
+			p += 10;
+			if (*p == '+' || *p == '-')
+				m += strtol(p, &p, 10);
+		}
+		else
+			m = strtol(p, &p, 10);
+		if (*p++ != ',')
+			bad("improper answer\n", re, s, -1, test);
+		if (*p == '?')
+		{
+			n = -1;
+			p++;
+		}
+		else if (*p == 'R' && !memcmp(p, "RE_DUP_MAX", 10))
+		{
+			n = RE_DUP_MAX;
+			p += 10;
+			if (*p == '+' || *p == '-')
+				n += strtol(p, &p, 10);
+		}
+		else
+			n = strtol(p, &p, 10);
+		if (*p++ != ')')
+			bad("improper answer\n", re, s, -1, test);
+		if (m!=match[i].rm_so || n!=match[i].rm_eo)
+		{
+			if (!(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY)))
+			{
+				report("failed: match was", NiL, re, s, len, NiL, flags, test);
+				matchprint(match, nmatch, nsub, ans, test);
+			}
+			return 0;
+		}
+	}
+	for (; i < nmatch; i++)
+	{
+		if (match[i].rm_so!=-1 || match[i].rm_eo!=-1)
+		{
+			if (!(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_VERIFY)))
+			{
+				if ((test & TEST_IGNORE_POSITION) && (match[i].rm_so<0 || match[i].rm_eo<0))
+				{
+					state.ignored++;
+					return 0;
+				}
+				if (!(test & TEST_SUMMARY))
+				{
+					report("failed: match was", NiL, re, s, len, NiL, flags, test);
+					matchprint(match, nmatch, nsub, ans, test);
+				}
+			}
+			return 0;
+		}
+	}
+	if (!(test & TEST_IGNORE_OVER) && match[nmatch].rm_so != state.NOMATCH.rm_so)
+	{
+		if (!(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY)))
+		{
+			report("failed: overran match array", NiL, re, s, len, NiL, flags, test);
+			matchprint(match, nmatch + 1, nsub, NiL, test);
+		}
+		return 0;
+	}
+	return 1;
+}
+
+static void
+sigunblock(int s)
+{
+#ifdef SIG_SETMASK
+	int		op;
+	sigset_t	mask;
+
+	sigemptyset(&mask);
+	if (s)
+	{
+		sigaddset(&mask, s);
+		op = SIG_UNBLOCK;
+	}
+	else op = SIG_SETMASK;
+	sigprocmask(op, &mask, NiL);
+#else
+#ifdef sigmask
+	sigsetmask(s ? (sigsetmask(0L) & ~sigmask(s)) : 0L);
+#endif
+#endif
+}
+
+static void
+gotcha(int sig)
+{
+	int	ret;
+
+	signal(sig, gotcha);
+	alarm(0);
+	state.signals++;
+	switch (sig)
+	{
+	case SIGALRM:
+		ret = REG_EHUNG;
+		break;
+	case SIGBUS:
+		ret = REG_EBUS;
+		break;
+	default:
+		ret = REG_EFAULT;
+		break;
+	}
+	sigunblock(sig);
+	longjmp(state.gotcha, ret);
+}
+
+static char*
+getline(FILE* fp)
+{
+	static char	buf[32 * 1024];
+
+	register char*	s = buf;
+	register char*	e = &buf[sizeof(buf)];
+	register char*	b;
+
+	for (;;)
+	{
+		if (!(b = fgets(s, e - s, fp)))
+			return 0;
+		state.lineno++;
+		s += strlen(s);
+		if (s == b || *--s != '\n' || s == b || *(s - 1) != '\\')
+		{
+			*s = 0;
+			break;
+		}
+		s--;
+	}
+	return buf;
+}
+
+static unsigned long
+note(unsigned long level, char* msg, unsigned long skip, unsigned long test)
+{
+	if (!(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_SUMMARY)) && !skip)
+	{
+		printf("NOTE\t");
+		if (msg)
+			printf("%s: ", msg);
+		printf("skipping lines %d", state.lineno);
+	}
+	return skip | level;
+}
+
+#define TABS(n)		&ts[7-((n)&7)]
+
+static char		ts[] = "\t\t\t\t\t\t\t";
+
+static unsigned long
+extract(int* tabs, char* spec, char* re, char* s, char* ans, char* msg, char* accept, regmatch_t* match, int nmatch, int nsub, unsigned long skip, unsigned long level, unsigned long test)
+{
+	if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_OK|TEST_PASS|TEST_SUMMARY))
+	{
+		state.extracted = 1;
+		if (test & TEST_OK)
+		{
+			state.passed++;
+			if ((test & TEST_VERIFY) && !(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_SUMMARY)))
+			{
+				if (msg && strcmp(msg, "EXPECTED"))
+					printf("NOTE\t%s\n", msg);
+				return skip;
+			}
+			test &= ~(TEST_PASS|TEST_QUERY);
+		}
+		if (test & (TEST_QUERY|TEST_VERIFY))
+		{
+			if (test & TEST_BASELINE)
+				test &= ~(TEST_BASELINE|TEST_PASS);
+			else
+				test |= TEST_PASS;
+			skip |= level;
+		}
+		if (!(test & TEST_OK))
+		{
+			if (test & TEST_UNSPECIFIED)
+				state.unspecified++;
+			else
+				state.errors++;
+		}
+		if (test & (TEST_PASS|TEST_SUMMARY))
+			return skip;
+		test &= ~TEST_DELIMIT;
+		printf("%s%s", spec, TABS(*tabs++));
+		if ((test & (TEST_BASELINE|TEST_SAME)) == (TEST_BASELINE|TEST_SAME))
+			printf("SAME");
+		else
+			quote(re, -1, test);
+		printf("%s", TABS(*tabs++));
+		quote(s, -1, test);
+		printf("%s", TABS(*tabs++));
+		if (!(test & (TEST_ACTUAL|TEST_BASELINE)) || !accept && !match)
+			printf("%s", ans);
+		else if (accept)
+			printf("%s", accept);
+		else
+			matchprint(match, nmatch, nsub, NiL, test);
+		if (msg)
+			printf("%s%s", TABS(*tabs++), msg);
+		putchar('\n');
+	}
+	else if (test & TEST_QUERY)
+		skip = note(level, msg, skip, test);
+	else if (test & TEST_VERIFY)
+		state.extracted = 1;
+	return skip;
+}
+
+static int
+catchfree(regex_t* preg, int flags, int* tabs, char* spec, char* re, char* s, char* ans, char* msg, char* accept, regmatch_t* match, int nmatch, int nsub, unsigned long skip, unsigned long level, unsigned long test)
+{
+	int	eret;
+
+	if (!(test & TEST_CATCH))
+	{
+		regfree(preg);
+		eret = 0;
+	}
+	else if (!(eret = setjmp(state.gotcha)))
+	{
+		alarm(HUNG);
+		regfree(preg);
+		alarm(0);
+	}
+	else if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+		extract(tabs, spec, re, s, ans, msg, NiL, NiL, 0, 0, skip, level, test);
+	else
+	{
+		report("failed", "regfree", re, NiL, -1, msg, flags, test);
+		error(preg, eret);
+	}
+	return eret;
+}
+
+static char*
+expand(char* os, char* ot)
+{
+	char*	s = os;
+	char*	t;
+	int	n = 0;
+	int	r;
+	long	m;
+
+	for (;;)
+	{
+		switch (*s++)
+		{
+		case 0:
+			break;
+		case '{':
+			n++;
+			continue;
+		case '}':
+			n--;
+			continue;
+		case 'R':
+			if (n == 1 && !memcmp(s, "E_DUP_MAX", 9))
+			{
+				s--;
+				for (t = ot; os < s; *t++ = *os++);
+				r = ((t - ot) >= 5 && t[-1] == '{' && t[-2] == '.' && t[-3] == '.' && t[-4] == '.') ? t[-5] : 0;
+				os = ot;
+				m = RE_DUP_MAX;
+				if (*(s += 10) == '+' || *s == '-')
+					m += strtol(s, &s, 10);
+				if (r)
+				{
+					t -= 5;
+					while (m-- > 0)
+						*t++ = r;
+					while (*s && *s++ != '}');
+				}
+				else
+					t += snprintf(t, 32, "%ld", m);
+				while (*t = *s++)
+					t++;
+				break;
+			}
+			continue;
+		default:
+			continue;
+		}
+		break;
+	}
+	return os;
+}
+
+int
+main(int argc, char** argv)
+{
+	int		flags;
+	int		cflags;
+	int		eflags;
+	int		nmatch;
+	int		nexec;
+	int		nstr;
+	int		cret;
+	int		eret;
+	int		nsub;
+	int		i;
+	int		j;
+	int		expected;
+	int		got;
+	int		locale;
+	int		subunitlen;
+	int		testno;
+	unsigned long	level;
+	unsigned long	skip;
+	char*		p;
+	char*		line;
+	char*		spec;
+	char*		re;
+	char*		s;
+	char*		ans;
+	char*		msg;
+	char*		fun;
+	char*		ppat;
+	char*		subunit;
+	char*		version;
+	char*		field[6];
+	char*		delim[6];
+	FILE*		fp;
+	int		tabs[6];
+	char		unit[64];
+	regmatch_t	match[100];
+	regex_t		preg;
+
+	static char	pat[32 * 1024];
+	static char	patbuf[32 * 1024];
+	static char	strbuf[32 * 1024];
+
+	int		nonosub = REG_NOSUB == 0;
+	int		nonexec = 0;
+
+	unsigned long	test = 0;
+
+	static char*	filter[] = { "-", 0 };
+
+	state.NOMATCH.rm_so = state.NOMATCH.rm_eo = -2;
+	p = unit;
+	version = (char*)id + 10;
+	while (p < &unit[sizeof(unit)-1] && (*p = *version++) && !isspace(*p))
+		p++;
+	*p = 0;
+	while ((p = *++argv) && *p == '-')
+		for (;;)
+		{
+			switch (*++p)
+			{
+			case 0:
+				break;
+			case 'c':
+				test |= TEST_CATCH;
+				continue;
+			case 'e':
+				test |= TEST_IGNORE_ERROR;
+				continue;
+			case 'h':
+			case '?':
+				help(0);
+				return 2;
+			case '-':
+				help(p[1] == 'h');
+				return 2;
+			case 'n':
+				nonexec = 1;
+				continue;
+			case 'o':
+				test |= TEST_IGNORE_OVER;
+				continue;
+			case 'p':
+				test |= TEST_IGNORE_POSITION;
+				continue;
+			case 's':
+#ifdef REG_DISCIPLINE
+				if (!(state.stack = stkalloc(stkstd, 0)))
+					fprintf(stderr, "%s: out of space [stack]", unit);
+				state.disc.disc.re_resizef = resizef;
+				state.disc.disc.re_resizehandle = (void*)stkstd;
+#endif
+				continue;
+			case 'x':
+				nonosub = 1;
+				continue;
+			case 'v':
+				test |= TEST_VERBOSE;
+				continue;
+			case 'A':
+				test |= TEST_ACTUAL;
+				continue;
+			case 'B':
+				test |= TEST_BASELINE;
+				continue;
+			case 'F':
+				test |= TEST_FAIL;
+				continue;
+			case 'P':
+				test |= TEST_PASS;
+				continue;
+			case 'S':
+				test |= TEST_SUMMARY;
+				continue;
+			default:
+				fprintf(stderr, "%s: %c: invalid option\n", unit, *p);
+				return 2;
+			}
+			break;
+		}
+	if (!*argv)
+		argv = filter;
+	locale = 0;
+	while (state.file = *argv++)
+	{
+		if (streq(state.file, "-") || streq(state.file, "/dev/stdin") || streq(state.file, "/dev/fd/0"))
+		{
+			state.file = 0;
+			fp = stdin;
+		}
+		else if (!(fp = fopen(state.file, "r")))
+		{
+			fprintf(stderr, "%s: %s: cannot read\n", unit, state.file);
+			return 2;
+		}
+		testno = state.errors = state.ignored = state.lineno = state.passed =
+		state.signals = state.unspecified = state.warnings = 0;
+		skip = 0;
+		level = 1;
+		if (!(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_SUMMARY)))
+		{
+			printf("TEST\t%s ", unit);
+			if (s = state.file)
+			{
+				subunit = p = 0;
+				for (;;)
+				{
+					switch (*s++)
+					{
+					case 0:
+						break;
+					case '/':
+						subunit = s;
+						continue;
+					case '.':
+						p = s - 1;
+						continue;
+					default:
+						continue;
+					}
+					break;
+				}
+				if (!subunit)
+					subunit = state.file;
+				if (p < subunit)
+					p = s - 1;
+				subunitlen = p - subunit;
+				printf("%-.*s ", subunitlen, subunit);
+			}
+			else
+				subunit = 0;
+			for (s = version; *s && (*s != ' ' || *(s + 1) != '$'); s++)
+				putchar(*s);
+			if (test & TEST_CATCH)
+				printf(", catch");
+			if (test & TEST_IGNORE_ERROR)
+				printf(", ignore error code mismatches");
+			if (test & TEST_IGNORE_POSITION)
+				printf(", ignore negative position mismatches");
+#ifdef REG_DISCIPLINE
+			if (state.stack)
+				printf(", stack");
+#endif
+			if (test & TEST_VERBOSE)
+				printf(", verbose");
+			printf("\n");
+#ifdef REG_VERSIONID
+			if (regerror(REG_VERSIONID, NiL, pat, sizeof(pat)) > 0)
+				s = pat;
+			else
+#endif
+#ifdef REG_TEST_VERSION
+			s = REG_TEST_VERSION;
+#else
+			s = "regex";
+#endif
+			printf("NOTE\t%s\n", s);
+			if (elementsof(unsupported) > 1)
+			{
+#if (REG_TEST_DEFAULT & (REG_AUGMENTED|REG_EXTENDED|REG_SHELL)) || !defined(REG_EXTENDED)
+				i = 0;
+#else
+				i = REG_EXTENDED != 0;
+#endif
+				for (got = 0; i < elementsof(unsupported) - 1; i++)
+				{
+					if (!got)
+					{
+						got = 1;
+						printf("NOTE\tunsupported: %s", unsupported[i]);
+					}
+					else
+						printf(",%s", unsupported[i]);
+				}
+				if (got)
+					printf("\n");
+			}
+		}
+#ifdef REG_DISCIPLINE
+		state.disc.disc.re_version = REG_VERSION;
+		state.disc.disc.re_compf = compf;
+		state.disc.disc.re_execf = execf;
+		if (!(state.disc.sp = sfstropen()))
+			bad("out of space [discipline string stream]\n", NiL, NiL, 0, 0);
+		preg.re_disc = &state.disc.disc;
+#endif
+		if (test & TEST_CATCH)
+		{
+			signal(SIGALRM, gotcha);
+			signal(SIGBUS, gotcha);
+			signal(SIGSEGV, gotcha);
+		}
+		while (p = getline(fp))
+		{
+
+		/* parse: */
+
+			line = p;
+			if (*p == ':' && !isspace(*(p + 1)))
+			{
+				while (*++p && *p != ':');
+				if (!*p++)
+				{
+					if (test & TEST_BASELINE)
+						printf("%s\n", line);
+					continue;
+				}
+			}
+			while (isspace(*p))
+				p++;
+			if (*p == 0 || *p == '#' || *p == 'T')
+			{
+				if (test & TEST_BASELINE)
+					printf("%s\n", line);
+				continue;
+			}
+			if (*p == ':' || *p == 'N')
+			{
+				if (test & TEST_BASELINE)
+					printf("%s\n", line);
+				else if (!(test & (TEST_ACTUAL|TEST_FAIL|TEST_PASS|TEST_SUMMARY)))
+				{
+					while (*++p && !isspace(*p));
+					while (isspace(*p))
+						p++;
+					printf("NOTE	%s\n", p);
+				}
+				continue;
+			}
+			j = 0;
+			i = 0;
+			field[i++] = p;
+			for (;;)
+			{
+				switch (*p++)
+				{
+				case 0:
+					p--;
+					j = 0;
+					goto checkfield;
+				case '\t':
+					*(delim[i] = p - 1) = 0;
+					j = 1;
+				checkfield:
+					s = field[i - 1];
+					if (streq(s, "NIL"))
+						field[i - 1] = 0;
+					else if (streq(s, "NULL"))
+						*s = 0;
+					while (*p == '\t')
+					{
+						p++;
+						j++;
+					}
+					tabs[i - 1] = j;
+					if (!*p)
+						break;
+					if (i >= elementsof(field))
+						bad("too many fields\n", NiL, NiL, 0, 0);
+					field[i++] = p;
+					/*FALLTHROUGH*/
+				default:
+					continue;
+				}
+				break;
+			}
+			if (!(spec = field[0]))
+				bad("NIL spec\n", NiL, NiL, 0, 0);
+
+		/* interpret: */
+
+			cflags = REG_TEST_DEFAULT;
+			eflags = REG_EXEC_DEFAULT;
+			test &= TEST_GLOBAL;
+			state.extracted = 0;
+			nmatch = 20;
+			nsub = -1;
+			for (p = spec; *p; p++)
+			{
+				if (isdigit(*p))
+				{
+					nmatch = strtol(p, &p, 10);
+					if (nmatch >= elementsof(match))
+						bad("nmatch must be < 100\n", NiL, NiL, 0, 0);
+					p--;
+					continue;
+				}
+				switch (*p)
+				{
+				case 'A':
+					test |= TEST_ARE;
+					continue;
+				case 'B':
+					test |= TEST_BRE;
+					continue;
+				case 'C':
+					if (!(test & TEST_QUERY) && !(skip & level))
+						bad("locale must be nested\n", NiL, NiL, 0, 0);
+					test &= ~TEST_QUERY;
+					if (locale)
+						bad("locale nesting not supported\n", NiL, NiL, 0, 0);
+					if (i != 2)
+						bad("locale field expected\n", NiL, NiL, 0, 0);
+					if (!(skip & level))
+					{
+#if defined(LC_COLLATE) && defined(LC_CTYPE)
+						s = field[1];
+						if (!s || streq(s, "POSIX"))
+							s = "C";
+						if ((ans = setlocale(LC_COLLATE, s)) && streq(ans, "POSIX"))
+							ans = "C";
+						if (!ans || !streq(ans, s) && streq(s, "C"))
+							ans = 0;
+						else if ((ans = setlocale(LC_CTYPE, s)) && streq(ans, "POSIX"))
+							ans = "C";
+						if (!ans || !streq(ans, s) && streq(s, "C"))
+							skip = note(level, s, skip, test);
+						else
+						{
+							if (!(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_SUMMARY)))
+								printf("NOTE	\"%s\" locale\n", s);
+							locale = level;
+						}
+#else
+						skip = note(level, skip, test, "locales not supported");
+#endif
+					}
+					cflags = NOTEST;
+					continue;
+				case 'E':
+					test |= TEST_ERE;
+					continue;
+				case 'K':
+					test |= TEST_KRE;
+					continue;
+				case 'L':
+					test |= TEST_LRE;
+					continue;
+				case 'S':
+					test |= TEST_SRE;
+					continue;
+
+				case 'a':
+					cflags |= REG_LEFT|REG_RIGHT;
+					continue;
+				case 'b':
+					eflags |= REG_NOTBOL;
+					continue;
+				case 'c':
+					cflags |= REG_COMMENT;
+					continue;
+				case 'd':
+					cflags |= REG_SHELL_DOT;
+					continue;
+				case 'e':
+					eflags |= REG_NOTEOL;
+					continue;
+				case 'f':
+					cflags |= REG_MULTIPLE;
+					continue;
+				case 'g':
+					cflags |= NOTEST;
+					continue;
+				case 'h':
+					cflags |= REG_MULTIREF;
+					continue;
+				case 'i':
+					cflags |= REG_ICASE;
+					continue;
+				case 'j':
+					cflags |= REG_SPAN;
+					continue;
+				case 'k':
+					cflags |= REG_ESCAPE;
+					continue;
+				case 'l':
+					cflags |= REG_LEFT;
+					continue;
+				case 'm':
+					cflags |= REG_MINIMAL;
+					continue;
+				case 'n':
+					cflags |= REG_NEWLINE;
+					continue;
+				case 'o':
+					cflags |= REG_SHELL_GROUP;
+					continue;
+				case 'p':
+					cflags |= REG_SHELL_PATH;
+					continue;
+				case 'q':
+					cflags |= REG_DELIMITED;
+					continue;
+				case 'r':
+					cflags |= REG_RIGHT;
+					continue;
+				case 's':
+					cflags |= REG_SHELL_ESCAPED;
+					continue;
+				case 't':
+					cflags |= REG_MUSTDELIM;
+					continue;
+				case 'u':
+					test |= TEST_UNSPECIFIED;
+					continue;
+				case 'v':
+					cflags |= REG_CLASS_ESCAPE;
+					continue;
+				case 'w':
+					cflags |= REG_NOSUB;
+					continue;
+				case 'x':
+					if (REG_LENIENT)
+						cflags |= REG_LENIENT;
+					else
+						test |= TEST_LENIENT;
+					continue;
+				case 'y':
+					eflags |= REG_LEFT;
+					continue;
+				case 'z':
+					cflags |= REG_NULL;
+					continue;
+
+				case '$':
+					test |= TEST_EXPAND;
+					continue;
+
+				case '/':
+					test |= TEST_SUB;
+					continue;
+
+				case '=':
+					test |= TEST_DECOMP;
+					continue;
+
+				case '?':
+					test |= TEST_VERIFY;
+					test &= ~(TEST_AND|TEST_OR);
+					state.verify = state.passed;
+					continue;
+				case '&':
+					test |= TEST_VERIFY|TEST_AND;
+					test &= ~TEST_OR;
+					continue;
+				case '|':
+					test |= TEST_VERIFY|TEST_OR;
+					test &= ~TEST_AND;
+					continue;
+				case ';':
+					test |= TEST_OR;
+					test &= ~TEST_AND;
+					continue;
+
+				case '{':
+					level <<= 1;
+					if (skip & (level >> 1))
+					{
+						skip |= level;
+						cflags = NOTEST;
+					}
+					else
+					{
+						skip &= ~level;
+						test |= TEST_QUERY;
+					}
+					continue;
+				case '}':
+					if (level == 1)
+						bad("invalid {...} nesting\n", NiL, NiL, 0, 0);
+					if ((skip & level) && !(skip & (level>>1)))
+					{
+						if (!(test & (TEST_BASELINE|TEST_SUMMARY)))
+						{
+							if (test & (TEST_ACTUAL|TEST_FAIL))
+								printf("}\n");
+							else if (!(test & TEST_PASS))
+								printf("-%d\n", state.lineno);
+						}
+					}
+#if defined(LC_COLLATE) && defined(LC_CTYPE)
+					else if (locale & level)
+					{
+						locale = 0;
+						if (!(skip & level))
+						{
+							s = "C";
+							setlocale(LC_COLLATE, s);
+							setlocale(LC_CTYPE, s);
+							if (!(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_SUMMARY)))
+								printf("NOTE	\"%s\" locale\n", s);
+							else if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_PASS))
+								printf("}\n");
+						}
+						else if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL))
+							printf("}\n");
+					}
+#endif
+					level >>= 1;
+					cflags = NOTEST;
+					continue;
+
+				default:
+					bad("bad spec\n", spec, NiL, 0, test);
+					break;
+
+				}
+				break;
+			}
+			if ((cflags|eflags) == NOTEST || (skip & level) && (test & TEST_BASELINE))
+			{
+				if (test & TEST_BASELINE)
+				{
+					while (i > 1)
+						*delim[--i] = '\t';
+					printf("%s\n", line);
+				}
+				continue;
+			}
+			if (test & TEST_OR)
+			{
+				if (!(test & TEST_VERIFY))
+				{
+					test &= ~TEST_OR;
+					if (state.passed == state.verify && i > 1)
+						printf("NOTE\t%s\n", field[1]);
+					continue;
+				}
+				else if (state.passed > state.verify)
+					continue;
+			}
+			else if (test & TEST_AND)
+			{
+				if (state.passed == state.verify)
+					continue;
+				state.passed = state.verify;
+			}
+			if (i < ((test & TEST_DECOMP) ? 3 : 4))
+				bad("too few fields\n", NiL, NiL, 0, test);
+			while (i < elementsof(field))
+				field[i++] = 0;
+			if (re = field[1])
+			{
+				if (streq(re, "SAME"))
+				{
+					re = ppat;
+					test |= TEST_SAME;
+				}
+				else
+				{
+					if (test & TEST_EXPAND)
+						escape(re);
+					re = expand(re, patbuf);
+					strcpy(ppat = pat, re);
+				}
+			}
+			else
+				ppat = 0;
+			nstr = -1;
+			if (s = field[2])
+			{
+				s = expand(s, strbuf);
+				if (test & TEST_EXPAND)
+				{
+					nstr = escape(s);
+#if _REG_nexec
+					if (nstr != strlen(s))
+						nexec = nstr;
+#endif
+				}
+			}
+			if (!(ans = field[(test & TEST_DECOMP) ? 2 : 3]))
+				bad("NIL answer\n", NiL, NiL, 0, test);
+			msg = field[4];
+			fflush(stdout);
+			if (test & TEST_SUB)
+#if _REG_subcomp
+				cflags |= REG_DELIMITED;
+#else
+				continue;
+#endif
+#if !_REG_decomp
+			if (test & TEST_DECOMP)
+				continue;
+#endif
+
+		compile:
+
+			if (state.extracted || (skip & level))
+				continue;
+#if !(REG_TEST_DEFAULT & (REG_AUGMENTED|REG_EXTENDED|REG_SHELL))
+#ifdef REG_EXTENDED
+			if (REG_EXTENDED != 0 && (test & TEST_BRE))
+#else
+			if (test & TEST_BRE)
+#endif
+			{
+				test &= ~TEST_BRE;
+				flags = cflags;
+				state.which = "BRE";
+			}
+			else
+#endif
+#ifdef REG_EXTENDED
+			if (test & TEST_ERE)
+			{
+				test &= ~TEST_ERE;
+				flags = cflags | REG_EXTENDED;
+				state.which = "ERE";
+			}
+			else
+#endif
+#ifdef REG_AUGMENTED
+			if (test & TEST_ARE)
+			{
+				test &= ~TEST_ARE;
+				flags = cflags | REG_AUGMENTED;
+				state.which = "ARE";
+			}
+			else
+#endif
+#ifdef REG_LITERAL
+			if (test & TEST_LRE)
+			{
+				test &= ~TEST_LRE;
+				flags = cflags | REG_LITERAL;
+				state.which = "LRE";
+			}
+			else
+#endif
+#ifdef REG_SHELL
+			if (test & TEST_SRE)
+			{
+				test &= ~TEST_SRE;
+				flags = cflags | REG_SHELL;
+				state.which = "SRE";
+			}
+			else
+#ifdef REG_AUGMENTED
+			if (test & TEST_KRE)
+			{
+				test &= ~TEST_KRE;
+				flags = cflags | REG_SHELL | REG_AUGMENTED;
+				state.which = "KRE";
+			}
+			else
+#endif
+#endif
+			{
+				if (test & (TEST_BASELINE|TEST_PASS|TEST_VERIFY))
+					extract(tabs, line, re, s, ans, msg, NiL, NiL, 0, 0, skip, level, test|TEST_OK);
+				continue;
+			}
+			if ((test & (TEST_QUERY|TEST_VERBOSE|TEST_VERIFY)) == TEST_VERBOSE)
+			{
+				printf("test %-3d %s ", state.lineno, state.which);
+				quote(re, -1, test|TEST_DELIMIT);
+				printf(" ");
+				quote(s, nstr, test|TEST_DELIMIT);
+				printf("\n");
+			}
+
+		nosub:
+			fun = "regcomp";
+#if _REG_nexec
+			if (nstr >= 0 && nstr != strlen(s))
+				nexec = nstr;
+
+			else
+#endif
+				nexec = -1;
+			if (state.extracted || (skip & level))
+				continue;
+			if (!(test & TEST_QUERY))
+				testno++;
+#ifdef REG_DISCIPLINE
+			if (state.stack)
+				stkset(stkstd, state.stack, 0);
+			flags |= REG_DISCIPLINE;
+			state.disc.ordinal = 0;
+			sfstrseek(state.disc.sp, 0, SEEK_SET);
+#endif
+			if (!(test & TEST_CATCH))
+				cret = regcomp(&preg, re, flags);
+			else if (!(cret = setjmp(state.gotcha)))
+			{
+				alarm(HUNG);
+				cret = regcomp(&preg, re, flags);
+				alarm(0);
+			}
+#if _REG_subcomp
+			if (!cret && (test & TEST_SUB))
+			{
+				fun = "regsubcomp";
+				p = re + preg.re_npat;
+				if (!(test & TEST_CATCH))
+					cret = regsubcomp(&preg, p, NiL, 0, 0);
+				else if (!(cret = setjmp(state.gotcha)))
+				{
+					alarm(HUNG);
+					cret = regsubcomp(&preg, p, NiL, 0, 0);
+					alarm(0);
+				}
+				if (!cret && *(p += preg.re_npat) && !(preg.re_sub->re_flags & REG_SUB_LAST))
+				{
+					if (catchfree(&preg, flags, tabs, line, re, s, ans, msg, NiL, NiL, 0, 0, skip, level, test))
+						continue;
+					cret = REG_EFLAGS;
+				}
+			}
+#endif
+#if _REG_decomp
+			if (!cret && (test & TEST_DECOMP))
+			{
+				char	buf[128];
+
+				if ((j = nmatch) > sizeof(buf))
+					j = sizeof(buf);
+				fun = "regdecomp";
+				p = re + preg.re_npat;
+				if (!(test & TEST_CATCH))
+					i = regdecomp(&preg, -1, buf, j);
+				else if (!(cret = setjmp(state.gotcha)))
+				{
+					alarm(HUNG);
+					i = regdecomp(&preg, -1, buf, j);
+					alarm(0);
+				}
+				if (!cret)
+				{
+					catchfree(&preg, flags, tabs, line, re, s, ans, msg, NiL, NiL, 0, 0, skip, level, test);
+					if (i > j)
+					{
+						if (i != (strlen(ans) + 1))
+						{
+							report("failed", fun, re, s, nstr, msg, flags, test);
+							printf(" %d byte buffer supplied, %d byte buffer required\n", j, i);
+						}
+					}
+					else if (strcmp(buf, ans))
+					{
+						report("failed", fun, re, s, nstr, msg, flags, test);
+						quote(ans, -1, test|TEST_DELIMIT);
+						printf(" expected, ");
+						quote(buf, -1, test|TEST_DELIMIT);
+						printf(" returned\n");
+					}
+					continue;
+				}
+			}
+#endif
+			if (!cret)
+			{
+				if (!(flags & REG_NOSUB) && nsub < 0 && *ans == '(')
+				{
+					for (p = ans; *p; p++)
+						if (*p == '(')
+							nsub++;
+						else if (*p == '{')
+							nsub--;
+					if (nsub >= 0)
+					{
+						if (test & TEST_IGNORE_OVER)
+						{
+							if (nmatch > nsub)
+								nmatch = nsub + 1;
+						}
+						else if (nsub != preg.re_nsub)
+						{
+							if (nsub > preg.re_nsub)
+							{
+								if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+									skip = extract(tabs, line, re, s, ans, msg, "OK", NiL, 0, 0, skip, level, test|TEST_DELIMIT);
+								else
+								{
+									report("re_nsub incorrect", fun, re, NiL, -1, msg, flags, test);
+									printf("at least %d expected, %d returned\n", nsub, preg.re_nsub);
+									state.errors++;
+								}
+							}
+							else
+								nsub = preg.re_nsub;
+						}
+					}
+				}
+				if (!(test & (TEST_DECOMP|TEST_SUB)) && *ans && *ans != '(' && !streq(ans, "OK") && !streq(ans, "NOMATCH"))
+				{
+					if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+						skip = extract(tabs, line, re, s, ans, msg, "OK", NiL, 0, 0, skip, level, test|TEST_DELIMIT);
+					else if (!(test & TEST_LENIENT))
+					{
+						report("failed", fun, re, NiL, -1, msg, flags, test);
+						printf("%s expected, OK returned\n", ans);
+					}
+					catchfree(&preg, flags, tabs, line, re, s, ans, msg, NiL, NiL, 0, 0, skip, level, test);
+					continue;
+				}
+			}
+			else
+			{
+				if (test & TEST_LENIENT)
+					/* we'll let it go this time */;
+				else if (!*ans || ans[0]=='(' || cret == REG_BADPAT && streq(ans, "NOMATCH"))
+				{
+					got = 0;
+					for (i = 1; i < elementsof(codes); i++)
+						if (cret==codes[i].code)
+							got = i;
+					if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+						skip = extract(tabs, line, re, s, ans, msg, codes[got].name, NiL, 0, 0, skip, level, test|TEST_DELIMIT);
+					else
+					{
+						report("failed", fun, re, NiL, -1, msg, flags, test);
+						printf("%s returned: ", codes[got].name);
+						error(&preg, cret);
+					}
+				}
+				else
+				{
+					expected = got = 0;
+					for (i = 1; i < elementsof(codes); i++)
+					{
+						if (streq(ans, codes[i].name))
+							expected = i;
+						if (cret==codes[i].code)
+							got = i;
+					}
+					if (!expected)
+					{
+						if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+							skip = extract(tabs, line, re, s, ans, msg, codes[got].name, NiL, 0, 0, skip, level, test|TEST_DELIMIT);
+						else
+						{
+							report("failed: invalid error code", NiL, re, NiL, -1, msg, flags, test);
+							printf("%s expected, %s returned\n", ans, codes[got].name);
+						}
+					}
+					else if (cret != codes[expected].code && cret != REG_BADPAT)
+					{
+						if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+							skip = extract(tabs, line, re, s, ans, msg, codes[got].name, NiL, 0, 0, skip, level, test|TEST_DELIMIT);
+						else if (test & TEST_IGNORE_ERROR)
+							state.ignored++;
+						else
+						{
+							report("should fail and did", fun, re, NiL, -1, msg, flags, test);
+							printf("%s expected, %s returned: ", ans, codes[got].name);
+							state.errors--;
+							state.warnings++;
+							error(&preg, cret);
+						}
+					}
+				}
+				goto compile;
+			}
+
+#if _REG_nexec
+		execute:
+			if (nexec >= 0)
+				fun = "regnexec";
+			else
+#endif
+				fun = "regexec";
+			
+			for (i = 0; i < elementsof(match); i++)
+				match[i] = state.NOMATCH;
+
+#if _REG_nexec
+			if (nexec >= 0)
+			{
+				eret = regnexec(&preg, s, nexec, nmatch, match, eflags);
+				s[nexec] = 0;
+			}
+			else
+#endif
+			{
+				if (!(test & TEST_CATCH))
+					eret = regexec(&preg, s, nmatch, match, eflags);
+				else if (!(eret = setjmp(state.gotcha)))
+				{
+					alarm(HUNG);
+					eret = regexec(&preg, s, nmatch, match, eflags);
+					alarm(0);
+				}
+			}
+#if _REG_subcomp
+			if ((test & TEST_SUB) && !eret)
+			{
+				fun = "regsubexec";
+				if (!(test & TEST_CATCH))
+					eret = regsubexec(&preg, s, nmatch, match);
+				else if (!(eret = setjmp(state.gotcha)))
+				{
+					alarm(HUNG);
+					eret = regsubexec(&preg, s, nmatch, match);
+					alarm(0);
+				}
+			}
+#endif
+			if (flags & REG_NOSUB)
+			{
+				if (eret)
+				{
+					if (eret != REG_NOMATCH || !streq(ans, "NOMATCH"))
+					{
+						if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+							skip = extract(tabs, line, re, s, ans, msg, "NOMATCH", NiL, 0, 0, skip, level, test|TEST_DELIMIT);
+						else
+						{
+							report("REG_NOSUB failed", fun, re, s, nstr, msg, flags, test);
+							error(&preg, eret);
+						}
+					}
+				}
+				else if (streq(ans, "NOMATCH"))
+				{
+					if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+						skip = extract(tabs, line, re, s, ans, msg, NiL, match, nmatch, nsub, skip, level, test|TEST_DELIMIT);
+					else
+					{
+						report("should fail and didn't", fun, re, s, nstr, msg, flags, test);
+						error(&preg, eret);
+					}
+				}
+			}
+			else if (eret)
+			{
+				if (eret != REG_NOMATCH || !streq(ans, "NOMATCH"))
+				{
+					if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+						skip = extract(tabs, line, re, s, ans, msg, "NOMATCH", NiL, 0, nsub, skip, level, test|TEST_DELIMIT);
+					else
+					{
+						report("failed", fun, re, s, nstr, msg, flags, test);
+						if (eret != REG_NOMATCH)
+							error(&preg, eret);
+						else if (*ans)
+							printf("expected: %s\n", ans);
+						else
+							printf("\n");
+					}
+				}
+			}
+			else if (streq(ans, "NOMATCH"))
+			{
+				if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+					skip = extract(tabs, line, re, s, ans, msg, NiL, match, nmatch, nsub, skip, level, test|TEST_DELIMIT);
+				else
+				{
+					report("should fail and didn't", fun, re, s, nstr, msg, flags, test);
+					matchprint(match, nmatch, nsub, NiL, test);
+				}
+			}
+#if _REG_subcomp
+			else if (test & TEST_SUB)
+			{
+				p = preg.re_sub->re_buf;
+				if (strcmp(p, ans))
+				{
+					report("failed", fun, re, s, nstr, msg, flags, test);
+					quote(ans, -1, test|TEST_DELIMIT);
+					printf(" expected, ");
+					quote(p, -1, test|TEST_DELIMIT);
+					printf(" returned\n");
+				}
+			}
+#endif
+			else if (!*ans)
+			{
+				if (match[0].rm_so != state.NOMATCH.rm_so)
+				{
+					if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+						skip = extract(tabs, line, re, s, ans, msg, NiL, NiL, 0, 0, skip, level, test);
+					else
+					{
+						report("failed: no match but match array assigned", NiL, re, s, nstr, msg, flags, test);
+						matchprint(match, nmatch, nsub, NiL, test);
+					}
+				}
+			}
+			else if (matchcheck(match, nmatch, nsub, ans, re, s, nstr, flags, test))
+			{
+#if _REG_nexec
+				if (nexec < 0 && !nonexec)
+				{
+					nexec = nstr >= 0 ? nstr : strlen(s);
+					s[nexec] = '\n';
+					testno++;
+					goto execute;
+				}
+#endif
+				if (!(test & (TEST_DECOMP|TEST_SUB|TEST_VERIFY)) && !nonosub)
+				{
+					if (catchfree(&preg, flags, tabs, line, re, s, ans, msg, NiL, NiL, 0, 0, skip, level, test))
+						continue;
+					flags |= REG_NOSUB;
+					goto nosub;
+				}
+				if (test & (TEST_BASELINE|TEST_PASS|TEST_VERIFY))
+					skip = extract(tabs, line, re, s, ans, msg, NiL, match, nmatch, nsub, skip, level, test|TEST_OK);
+			}
+			else if (test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS|TEST_QUERY|TEST_SUMMARY|TEST_VERIFY))
+				skip = extract(tabs, line, re, s, ans, msg, NiL, match, nmatch, nsub, skip, level, test|TEST_DELIMIT);
+			if (catchfree(&preg, flags, tabs, line, re, s, ans, msg, NiL, NiL, 0, 0, skip, level, test))
+				continue;
+			goto compile;
+		}
+		if (test & TEST_SUMMARY)
+			printf("tests=%-4d errors=%-4d warnings=%-2d ignored=%-2d unspecified=%-2d signals=%d\n", testno, state.errors, state.warnings, state.ignored, state.unspecified, state.signals);
+		else if (!(test & (TEST_ACTUAL|TEST_BASELINE|TEST_FAIL|TEST_PASS)))
+		{
+			printf("TEST\t%s", unit);
+			if (subunit)
+				printf(" %-.*s", subunitlen, subunit);
+			printf(", %d test%s", testno, testno == 1 ? "" : "s");
+			if (state.ignored)
+				printf(", %d ignored mismatche%s", state.ignored, state.ignored == 1 ? "" : "s");
+			if (state.warnings)
+				printf(", %d warning%s", state.warnings, state.warnings == 1 ? "" : "s");
+			if (state.unspecified)
+				printf(", %d unspecified difference%s", state.unspecified, state.unspecified == 1 ? "" : "s");
+			if (state.signals)
+				printf(", %d signal%s", state.signals, state.signals == 1 ? "" : "s");
+			printf(", %d error%s\n", state.errors, state.errors == 1 ? "" : "s");
+		}
+		if (fp != stdin)
+			fclose(fp);
+	}
+	return 0;
+}