That way we don't have to decode this too in the subclasses.
prefix with _, use frame type directly, use needs_swap rather than is_native so it's more clear to readers.
We will eventually be adding sub-types for the various frame types, and use this as a common ancestor for item inflation.
This will provide better namespacing for the objects inflated from the document for various frame types. By creating real objects with real properties we give ourselves quite a bit of flexibility in the data filtering language coming forth.
