enhancements. Particularly prominent performance optimisations could go
here, but most should go in the L</Performance Enhancements> section.
+=head2 Non-destructive substitution
+
+The substitution operator now supports a C</r> option that
+copies the input variable, carries out the substitution on
+the copy and returns the result. The original remains unmodified.
+
+ my $old = 'cat';
+ my $new = $old =~ s/cat/dog/r;
+ # $old is 'cat' and $new is 'dog'
+
+This is particularly useful with C<map>. See L<perlop> for more examples.
+
=head1 New Platforms
XXX List any platforms that this version of perl compiles on, that previous