strings: clarify usage of Title and ToTitle

This is intended to help clear up confusion around the usage of the
Title and ToTitle functions. It includes a link to define title case
to distinguish it from upper case. It also includes an additional
example for the ToTitle function to showcase the difference in behavior
between it and the Title function.

Fixes #33302

Change-Id: I44e62962fb04d0d22966a39eda3a2d16de7a2291
Reviewed-on: https://go-review.googlesource.com/c/go/+/187825Reviewed-by: Rob Pike <r@golang.org>

src/strings/example_test.go

@@ -247,14 +247,23 @@ func ExampleSplitAfterN() {
 }
 
 func ExampleTitle() {
+	// Compare this example to the ToTitle example.
 	fmt.Println(strings.Title("her royal highness"))
-	// Output: Her Royal Highness
+	fmt.Println(strings.Title("loud noises"))
+	fmt.Println(strings.Title("хлеб"))
+	// Output:
+	// Her Royal Highness
+	// Loud Noises
+	// Хлеб
 }
 
 func ExampleToTitle() {
+	// Compare this example to the Title example.
+	fmt.Println(strings.ToTitle("her royal highness"))
 	fmt.Println(strings.ToTitle("loud noises"))
 	fmt.Println(strings.ToTitle("хлеб"))
 	// Output:
+	// HER ROYAL HIGHNESS
 	// LOUD NOISES
 	// ХЛЕБ
 }

src/strings/strings.go

@@ -610,7 +610,8 @@ func ToLower(s string) string {
 	return Map(unicode.ToLower, s)
 }
 
-// ToTitle returns a copy of the string s with all Unicode letters mapped to their title case.
+// ToTitle returns a copy of the string s with all Unicode letters mapped to
+// their Unicode title case.
 func ToTitle(s string) string { return Map(unicode.ToTitle, s) }
 
 // ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their
@@ -626,7 +627,7 @@ func ToLowerSpecial(c unicode.SpecialCase, s string) string {
 }
 
 // ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their
-// title case, giving priority to the special casing rules.
+// Unicode title case, giving priority to the special casing rules.
 func ToTitleSpecial(c unicode.SpecialCase, s string) string {
 	return Map(c.ToTitle, s)
 }
@@ -707,7 +708,7 @@ func isSeparator(r rune) bool {
 }
 
 // Title returns a copy of the string s with all Unicode letters that begin words
-// mapped to their title case.
+// mapped to their Unicode title case.
 //
 // BUG(rsc): The rule Title uses for word boundaries does not handle Unicode punctuation properly.
 func Title(s string) string {