=head2 Variable length lookbehind in regular expression pattern matching
is now experimentally supported
-Using a lookbehind assertion (like C<(?<=foo)> or C<(?<!bar)> previously
+Using a lookbehind assertion (like C<(?<=foo?)> or C<(?<!ba{1,9}r)> previously
would generate an error and refuse to compile. Now it compiles (if the
maximum lookbehind is at most 255 characters), but raises a warning in
the new C<experimental::vlb> warnings category. This is to caution you