Collection is a subpattern of the container pattern and is the abstract superpattern for all position independent container patterns in the container libraries, defining all common attributes of these patterns.
Collection defines the following additional attributes:
insert: takes an element reference and inserts the element in the collection.
delete: takes an element reference and deletes that element from the collection.
union: takes a reference to another collection, and unifies the elements in both collections into this(collection).