* starts at the same time as the event to add, it is replaced by the new
* event. If the new event starts before the zoomed event list's last event,
* the new event is ignored and is assumed to be already part of the list.
* starts at the same time as the event to add, it is replaced by the new
* event. If the new event starts before the zoomed event list's last event,
* the new event is ignored and is assumed to be already part of the list.