The requirement to put the version and/or retrieval time in as a child element sort of violates the rule about Extent in 9.3, which is that you only use non-refs for primitive children with no further extent; complex children should generally be represented with refs. Conceptually I think it’s helpful not to have to ask again for these additional details, but it is the first place a client looks, and it violates the rule. The ‘rule’ is a should, not a must, so it’s not a definite problem, but still worth noting and considering.