Think of it as a persistent DOM with versioning functionality especially well suited for flash-based storage. Furthermore diff-algorithms facilitate the import of differences between tree-structures. A GUI which currently needs some work to be up to date with the core-projects facilitates a Visual Analytics approach for comparing tree-structures through a bunch of interactive visualizations on top of the diff-algorithms. Saxon is usable to query the system. However I'm currently working on incremental indexes to support an upcoming brackit.org binding for full XQuery 1.0 and XQuery Update Facility support with a query optimizer.