ReadonlyACTOR: "actor"The action is targeted at the actor of the item that owns the action, or if the owner is an actor, then the actor itself.
ReadonlyITEM: "item"The action is targeted at the item that owns the action, or if the owner is not an item, then the action has no effect.
ReadonlyOTHER: "other"The action is targeted at something else.
ReadonlySELF: "self"The action is targeted at the document that owns the action.
Map of action-scope key → value.