Objects of a partitioned type
When data objects of different types appear in the same place in the data, the types must be distinguishable. The data must be distinguishable in the type definition. When a partition is part of a partitioned object, the process of cycling through the partitioned subtree begins to make the determination of which partition the data object belongs to.
In a partitioned type, each partition must be content-distinguishable from the type of each partition that follows it.