Allow attaching schemas to proxies:
- one or more schemas to be available on all proxies (independently of the type of the doc to which a proxy points),
- read/write of properties on the proxy for this schema goes to the proxy's data,
- queries on this schema for proxies go to the proxy's data,
- if the same schema is available on the document to which a proxy points then it is hidden (shadowed) when accessing through the proxy.
Note, ACLs already behave this way (except for the query part which doesn't exist).