Bags cover all collection types including arrays, collections, lists, sets, (but excluding Maps - see the next section for those), and are implemented client-side as a Javascript array. When calling a component method that accepts one of these types as a parameter, your parameter should be a Javascript array. If a component method returns one of these types, then the return value will also be a Javascript array. The remoting framework is clever enough on the server side to convert the bag to an appropriate type for the component method call.