You need to register the property name, the namespace. One attendee asked whether it makes sense to register an entire namespace, in order to assert that this is a namespace I am going to use, and I want people to know. Larry Masinter stated, in his view, a property registry is almost useless. What people do with properties is they build protocols out of them. Properties rarely have an independent, separable semantics from other properties.
People define a suite of properties and then implement a protocol that goes along with it.
The suite of properties mean something together. Registering properties without defining their relationship is like defining a registry of HTTP headers without defining their relationships. A registry of XML elements doesn't tell you the semantics of the constructions you build out of them. Defining a registry by defining the properties alone is insufficient. Larry continued, stating that you need the whole schema.