Uses that are functioning in two directions, e.g. books that can be read from both sides.
Contributed by Filipe Lampejo
Contributed by Stéphane Darricau
Contributed by Jean Wojciechowski
Contributed by Sven Sorić
Contributed by Wibke Bramesfeld
Contributed by Jolin Masson
Contributed by Nolan Paparelli
Contributed by Gareth Hague