+=item User-defined case-mapping '%s' is deprecated
+
+(W deprecated) You defined a function, such as C<ToLower> that overrides
+the standard case mapping, such as C<lc()> gives. This feature is being
+deprecated due to its many issues, as documented in
+L<perlunicode/User-Defined Case Mappings (for serious hackers only)>.
+It is planned to remove this feature in Perl 5.16. A CPAN module
+providing improved functionality is being prepared.
+