This is a controlling interface for containers that have an unknown (at compile time) or
potentially large number of children (such as an address book). To prevent the need to
load ALL children when the container is created, the IVfsCacheContainer
will create and
destroy child nodes on-the-fly, as they are required. To do this, each IVfsCacheContainer
has a number of cache slots that hold 'active' children (i.e. children that are being observed
or read). Once a child becomes inactive, it may be removed from its cache slot and deleted, and
the cache slot re-used.