A Subindex<T,TKey> is attached to its parent index definition, which is an Index<T,TKey> or another Subindex<T,TKey>. The subindexes collection is stored in the parent's IndexDefinition<T>.Subindexes property.
Subindexes are optional, not required for any indexing tasks, but can provide additional optimization and help minimize memory requirements when a collection is indexed by multi-level (multi-field) keys.
System.Object
C1.LiveLinq.Indexing.SubindexCollection<T>