set o [new Observer]
Observer objects are user interface elements). Usually, you do not create objects that are directly of the Observer class. Instead, other classes derive from this class.
$o update $event ...
The Observer defines a default update method that is invoked whenever an Observable entity has an event for the Observer. The default update method looks for a method with the same name as the event that occurred. If there is such a method associated with the Observer object, it invokes the method with any additional arguments that might have been passed to update. If no such method exists, the update method simply ignores the event.
Returns: Nothing.