Jeff:
As for the certificates field, it is a SET OF, not a SEQUENCE OF.
Therefore, there is no meaning to the order of certificates found in
there. In fact, if someone's software is automatically encoding as DER
(as opposed to BER) then the ordering will be strictly according to the
encoded bytes of each certificate - that is, irrelevant of the meaning of
each certificate. The certificates field is therefore an unordered
"bag o' certificates". The same goes for CRLs.
The use of "SEQUENCE OF" is necessary when order is important, but it can
also be used when order is not important. And, it has much less overhead
that "SET OF" when DER is used since a sort is not required. Either
"SEQUENCE OF" or "SET OF" can be used to carry a "bag o' certificates".
I see no benefit to "SET OF."
Russ