Abstract: An annotation system includes first annotation data for annotating a manifestation of a first instance of a first XML document. The first instance of the first XML document is served by a document system. The first annotation data includes a first XML document identifier for the first XML document. The first annotation data is uniquely identified by a first annotation data identifier. The document system is configured to respond to a request containing the first XML document identifier with a manifestation of a second instance of the first XML document. The annotation system: (A) receives a request containing the first annotation data identifier; (B) issues a request containing the first XML document identifier to the document system; and (C) in response to the request containing the first annotation data identifier, manifests the first annotation data in connection with a manifestation of a second instance of the XML document.