ICU-22722 toTitle does not use UTR 21

icu4c/source/common/unicode/ucasemap.h

@@ -202,8 +202,8 @@ ucasemap_setBreakIterator(UCaseMap *csm, UBreakIterator *iterToAdopt, UErrorCode
  *
  * The titlecase break iterator can be provided to customize for arbitrary
  * styles, using rules and dictionaries beyond the standard iterators.
- * The standard titlecase iterator for the root locale implements the
- * algorithm of Unicode TR 21.
+ * If the break iterator passed in is null, the default Unicode algorithm
+ * will be used to determine the titlecase positions.
  *
  * This function uses only the setText(), first() and next() methods of the
  * provided break iterator.
@@ -312,8 +312,8 @@ ucasemap_utf8ToUpper(const UCaseMap *csm,
  *
  * The titlecase break iterator can be provided to customize for arbitrary
  * styles, using rules and dictionaries beyond the standard iterators.
- * The standard titlecase iterator for the root locale implements the
- * algorithm of Unicode TR 21.
+ * If the break iterator passed in is null, the default Unicode algorithm
+ * will be used to determine the titlecase positions.
  *
  * This function uses only the setUText(), first(), next() and close() methods of the
  * provided break iterator.

icu4c/source/common/unicode/unistr.h

@@ -2793,8 +2793,8 @@ class U_COMMON_API UnicodeString : public Replaceable
    * styles, using rules and dictionaries beyond the standard iterators.
    * It may be more efficient to always provide an iterator to avoid
    * opening and closing one for each string.
-   * The standard titlecase iterator for the root locale implements the
-   * algorithm of Unicode TR 21.
+   * If the break iterator passed in is null, the default Unicode algorithm
+   * will be used to determine the titlecase positions.
    *
    * This function uses only the setText(), first() and next() methods of the
    * provided break iterator.
@@ -2821,8 +2821,8 @@ class U_COMMON_API UnicodeString : public Replaceable
    * styles, using rules and dictionaries beyond the standard iterators.
    * It may be more efficient to always provide an iterator to avoid
    * opening and closing one for each string.
-   * The standard titlecase iterator for the root locale implements the
-   * algorithm of Unicode TR 21.
+   * If the break iterator passed in is null, the default Unicode algorithm
+   * will be used to determine the titlecase positions.
    *
    * This function uses only the setText(), first() and next() methods of the
    * provided break iterator.
@@ -2850,8 +2850,8 @@ class U_COMMON_API UnicodeString : public Replaceable
    * styles, using rules and dictionaries beyond the standard iterators.
    * It may be more efficient to always provide an iterator to avoid
    * opening and closing one for each string.
-   * The standard titlecase iterator for the root locale implements the
-   * algorithm of Unicode TR 21.
+   * If the break iterator passed in is null, the default Unicode algorithm
+   * will be used to determine the titlecase positions.
    *
    * This function uses only the setText(), first() and next() methods of the
    * provided break iterator.

icu4c/source/common/unicode/ustring.h

@@ -1107,8 +1107,8 @@ u_strToLower(UChar *dest, int32_t destCapacity,
  * styles, using rules and dictionaries beyond the standard iterators.
  * It may be more efficient to always provide an iterator to avoid
  * opening and closing one for each string.
- * The standard titlecase iterator for the root locale implements the
- * algorithm of Unicode TR 21.
+ * If the break iterator passed in is null, the default Unicode algorithm
+ * will be used to determine the titlecase positions.
  *
  * This function uses only the setText(), first() and next() methods of the
  * provided break iterator.