=item Malformed UTF-8 character (%s)
-(S utf8) (F) Perl detected something that didn't comply with UTF-8
-encoding rules.
+(S utf8) (F) Perl detected a string that didn't comply with UTF-8
+encoding rules, even though it had the UTF8 flag on.
-One possible cause is that you read in data that you thought to be in
-UTF-8 but it wasn't (it was for example legacy 8-bit data). Another
-possibility is careless use of utf8::upgrade().
+One possible cause is that you set the UTF8 flag yourself for data that
+you thought to be in UTF-8 but it wasn't (it was for example legacy
+8-bit data). To guard against this, you can use Encode::decode_utf8.
+
+If you use the C<:encoding(UTF-8)> PerlIO layer for input, invalid byte
+sequences are handled gracefully, but if you use C<:utf8>, the flag is
+set without validating the data, possibly resulting in this error
+message.
+
+See also L<Encode/"Handling Malformed Data">.
=item Malformed UTF-16 surrogate
(S internal) An internal warning that the grammar is screwed up.
+=item Opening dirhandle %s also as a file
+
+(W io deprecated) You used open() to associate a filehandle to
+a symbol (glob or scalar) that already holds a dirhandle.
+Although legal, this idiom might render your code confusing
+and is deprecated.
+
+=item Opening filehandle %s also as a directory
+
+(W io deprecated) You used opendir() to associate a dirhandle to
+a symbol (glob or scalar) that already holds a filehandle.
+Although legal, this idiom might render your code confusing
+and is deprecated.
+
=item Operation "%s": no method found, %s
(F) An attempt was made to perform an overloaded operation for which no
=item Warning: something's wrong
(W) You passed warn() an empty string (the equivalent of C<warn "">) or
-you called it with no args and C<$_> was empty.
+you called it with no args and C<$@> was empty.
=item Warning: unable to close filehandle %s properly