David,
This doesn't have the appearance of a non-normative note. And, as Marty has
mentioned, it may be worthwhile limiting this to a disclaimer:
"persistDuration doesn't have anything to do with message order
implementation." Some explanation might be sensible.
This goes the other way, recommending a specific implementation.
I recommended, in my comments on the schema and the second half, removal of
the messageOrderSemantics attribute and requiring SequenceNumber in
MessageOrder. The current module is more complicated than necessary,
seemingly allowing a sender to provide information the receiver can randomly
choose to use. It raises a red flag to see text like "X element MUST appear
when Y attribute has the value Z".
thanx,
doug