How is DocumentReference.content.attachment to be used when the content is a document Bundle? Must the document Bundle be seralized into a Binary? It seems logical that DocumentReference.content.attachment.url could point at the document Bundle, but it is not clear given that this element is a url datatype and not a Reference datatype. If the solution is to just have the URL be the full URL to the Bundle, then please indicate that in the DocumentReference notes. If this is the solution, then what would the mapping be, other than the existing mapping from Composition. That is to ask should the Bundle id or Bundle identifier be preserved somewhere in the DocumentReference? Might this go into DocumentReference.content.identifier rather than the Composition.identifier?