This could be added as an optional feature with no impact to existing
implementations. I would like implementers to study the feasibility and
impact of this change.
See this thread for discussion and example:
http://lists.oasis-open.org/archives/xacml-comment/200810/msg00001.html.
Here is the use case that is illustrated in the example in that thread:
When defining a product structure from re-usable components, you want to
detect or prevent adding an export-controlled component into a
non-export-controlled assembly. The rule can be written very simply by
using the ancestor list of each descendant node. However, since the
initial context is always the root of