ContainsAll returns true if this set of resources contains that set of (presumably pre-validated) resources.

Flatten is deprecated and should only be used when dealing w/ resources in pre-reservation-refinement format.

Reduce applies the given Reducer to produce a final Resource, iterating left-to-right over the given resources; panics if the Reducer is nil.

Reducer applies some operation to possibly combine an accumulator (acc) and a resource (x), returning either the combined result or nil.