Regarding Draft -08
Assume no base uri for posted entries
Entries being posted to a collection have no base uri.
Add to section 8.1
Within an Atom Entry document that is being posted to create a new entry, the BASE URI [RFC3896#sec-reference] is not defined, unless explicitly specified within the Entry Document, for example with xml:base. Thus, these Atom Entry documents SHOULD NOT include relative URI references [RFC3986#sec-ref]