What about the XML Information Set?
The W3C's XML Information Set project is a great thing, and it is urgently needed in order to allow the addresses of XML document components to be interchangeable.
If the XML Information Set were expressed as a “Property Set”, then it would be a description of a grove -- an XML grove. In any case, it will be very similar to a property set for XML.
The XML Information Set is expected to be a description of the features of XML, but not described in a fashion that could be used for other notations.