def add_event_listener(evt, callback):
    """
        Add a listener to an Event object. This may be called multiple
        times for the same event. Every time the event happens, the
        callback method will be called. The callback has one argument
        (a string, the contents of the event, minus the '650' and the
        name of the event)

        FIXME: should have an interface for the callback.
        """
