|integer||Optional: The numeric index of the event to get label of|
Checks whether the specified event has been previously viewed or not and returns 'true' or 'false'. If no event is specified, the current event will be checked instead. If the event cannot be found, 'false' will be returned.
This can be used, for example, to create a "skip read" button for visual novels where users are expected to retread common sections while navigating through branching story paths.