Referential Members (3)
3.1.7 It is possible to add a referential member to a collection.
3.1.8 It is possible to remove a referential member from a collection.
3.1.9 It is possible for a referential member of a collection to carry its own properties, distinct from those of the resource it refers to.
3.1.15 A referential member of a collection is itself a resource.