Changes in an XML document may affect not only element and attribute content but, more problematically, the markup hierarchy. Markup for tracking structural changes must represent multiple, often overlapping, structures in the same document. Thus, the perennial problem of overlap becomes a subset of the problem of managing change to structured documents, such as versions of documents amended over time.
We have developed changes to the delta file. This new representation allows us to define overlapping hierarchies in a completely XML way without declaring a dominant hierarchy and while keeping element fragmentation to a minimum.