> In Section 5, business rule #2 states:
 >
 > "Nonzas SHOULD NOT have a 'from' or 'to' attribute."
 >
 > I have a few questions:
 >
 > - When is it sensible to make an exception to this SHOULD NOT?

I can not think of one. However, this does not mean that there may be
one, hence the defensive wording.


 > - How should the 'from' and especially 'to' attributes be handled in the
 > light of RFC 6120 §4.7?

Hard to answer without any experience with Nonzas carrying a 'from' or
'to' attribute.