Ratings do not have to be embedded in the document. PICS-NG is like PICS but uses XML so you can define your own tags. Many ways to associate assertions and resources. Can reify properties so they can be assigned properties. RDF has defined serialization, assertions, and structure.
Client can manipulate objects from client.
Class hierarchy rooted at document with HTML and XML subtypes. You get a generic interface. A purchase order is a generic object. Use Java tag for object code. Use RDF to define relations to other code.