Which definition of putExtra is used when a Messenger is packed into an Intent

I am starting a Service from an Activity by passing an Intent like this:

intent.putExtra("MESSENGER", new Messenger(handler));

The above line works correctly, but I would like to understand how it works since I have not converted the Messenger into a Parcel. Is this definition of putExtra being used?

putExtra(String name, Serializable value) 

-Amit