Description:
------------
---
From manual page: http://www.php.net/class.serializable
---
> Classes that implement this interface no longer support __sleep() and
> __wakeup().

There is, however, a notable exception: when an instance of such a class is
unserialized from a old representation ("O" instead of "C"), __wakeup() is
called (and not unserialize()). That feature can be very helpful for migration
(e.g. session data), but might also cause confusion, unless it's documented.