This is an optimization over getNode to get many nodes in one call. If
the transport implementation does not optimize, it can just loop over the
paths and call getNode repeatedly.
If a transport can do it, it should also implement
NodeTypeFilterInterface.
For prefetch, there are two mechanisms: As with getNode, the stdClass
structure may be recursive. Additionally, the transport is allowed to
return additional entries that where not requested in the returned
array. Jackalope takes care of only returning nodes that where actually
requested by the client and caching the rest.