Hi Erik. FYI, if you look at the final section of appendix A you'll
see that we do actually require that no extensions introduce side-
effects. A big part of this was explicitly because of concerns over re-
ordering operation. Of course, I don't think we say the same thing
about policy reference/retrieval, so theoretically you could still
introduce side-effects at the policy-combining level.
Certainly the spec is supposed to allow you to re-order many aspects
of evaluation, though I think it does this by omission of any specific
prohibitions rather than any explicit statement. For what it's worth,
I think it's ok to include some comment about allowing re-ordering, as
long as it doesn't confuse people into thinking that there's an
obvious way that things *should* be re-ordered in practice. I think
part of why we never called this out explicitly was to make sure that
when people first look at XACML, they focus on the basic in-order,
recursive model, and then start thinking about how to extend it.
seth
