regexp: add example for ReplaceAll

Updates #21450

Change-Id: Ia31c20b52bae5daeb33d918234c2f0944a8aeb07
GitHub-Last-Rev: cc8554477024277c3c1b4122344e9d14427680b3
GitHub-Pull-Request: golang/go#33489
Reviewed-on: https://go-review.googlesource.com/c/go/+/189137
Run-TryBot: Sylvain Zimmer <sylvinus@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/regexp/example_test.go

@@ -181,6 +181,19 @@ func ExampleRegexp_MatchString() {
 	// true
 }
 
+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")))
+	// Output:
+	// -T-T-
+	// --xx-
+	// ---
+	// -W-xxW-
+}
+
 func ExampleRegexp_ReplaceAllLiteralString() {
 	re := regexp.MustCompile(`a(x*)b`)
 	fmt.Println(re.ReplaceAllLiteralString("-ab-axxb-", "T"))