WhenAbsent
What a page that does not hold the entity an event’s field names receives: each field that holds an entity declares one. A page that held the entity until it was destroyed holds it for this, and reads null there under either, as every world’s reader does once it is gone.
Enumeration Members
Section titled “Enumeration Members”Null:
"null"
The page receives the event with null in the field, and a list without the entity: a hit’s source, so a victim flinches without learning who struck her.
Withhold
Section titled “Withhold”Withhold:
"withhold"
The page receives no such event: a trigger’s entrant, whom a page that cannot see her must not learn stood on the plate.