This class implements an event. It is something that happens along the turn duration and it is hard to represent as an attribute because it just happen and disappear after that or because it happens several times per turn.
One interesting example of this would be private chat.
When you write private messages, it is added inside the target player, but you can't represent that as an attribute because it two private chat messages happen at the same time, one of them would be lost.
So solution to this problem is add each them as RPEvent.
A RPEvent is always linked to an RPObject.
@author miguel, hendrik