Tied filehandles are still incomplete. sysopen(), truncate(),
flock(), fcntl(), stat() and -X can't currently be trapped.
+The bucket usage information provided by C<scalar(%hash)> is not
+available. If C<%hash> is tied, this will currently result in a
+fatal error.
+
+Counting the number of entries in a hash via C<scalar(keys(%hash))> or
+C<scalar(values(%hash)>) is inefficient since it needs to iterate
+through all the entries with FIRSTKEY/NEXTKEY.
+
=head1 AUTHOR
Tom Christiansen