platforms without change. Attempts to change the locale away from the
"C" locale will, of course, fail.
+=head2 PERL_DEBUG_READONLY_COW
+
+On some operating systems Perl can be compiled in such a way that any
+attempt to modify string buffers shared by multiple SVs will crash. This
+way XS authors can test that their modules handle copy-on-write scalars
+correctly. See L<perlguts/"Copy on Write"> for detail.
+
+This feature was actually added in 5.19.8, but was unintentionally omitted
+from its delta document.
+
=head1 Security
XXX Any security-related notices go here. In particular, any security
However, any changes to F<pod/perldiag.pod> should go in the L</Diagnostics>
section.
-=head3 L<XXX>
+=head3 L<perlguts>
=over 4
=item *
-XXX Description of the change here
+New sections on L<Read-Only Values|perlguts/"Read-Only Values"> and
+L<Copy on Write|perlguts/"Copy on Write"> have been added. They were
+actually added in 5.19.8 but accidentally omitted from its delta document.
=back