the action to register.
the result of the action if it is immediate, or true if it is deferred.
Execute all deferred actions that have been added to the handler. This should be called after processing rules to ensure that all deferred command actions are executed.
A promise that resolves when all deferred actions have been executed.
Add an action to the handler. Each action must have a unique hash that identifies it. If an action with the same hash is already registered, an error will be thrown. If the action is marked as immediate, it will be executed immediately using the associated plugin. If the action is deferred, it will be stored for later execution when executeDeferred() is called.