Internally, the contents of a container can be stored as one or more requests. The atomic parts of the container contents is interface, model, resource and sub-request.
The use of sub-requests, et al, will sometimes save a lot of time and space, because wo don't have to know exactly what resources are contained in the container until someone actualy wants to iterate through the members or determine an exact size.
Iteraters can be used to avoid having all the elements in memory.
See the API for examples.
Not implemented