CD-1 issue #15: ancestor attributes of XML nodes

The issue number refers to the XLS-sheet found in this email:
http://lists.oasis-open.org/archives/xacml/200909/msg00013.html

The commenter says that the ancestor attributes in the XML case are not 
needed since the hierarchy information is already there in the XML document.

The attributes are intended to be used with the xpath match functions to 
grant access to sections of an XML document. It is probably true that 
these attributes are redundant since it is probably possible to achieve 
the same effect using xpath expressions which match sections of the XML 
document.

However, I have not done a careful analysis of whether this is really 
true, or which approach is more efficient. Also, it would be good to 
keep the attributes for compatibility with XACML 2.0.

So I propose that we make no change.

Best regards,
Erik