Implications of "set require-order no"

[Maxim Khitrov]

Hello all,

The "require-order" option has the following ominous warning:

"There may be non-trivial and non-obvious implications to an out of
order ruleset. Consider carefully before disabling the order
enforcement."

In OpenBSD 4.6 this directive was changed to 'no' by default, and it
was taken out completely in 5.0. Can someone please clarify what are
these "non-trivial and non-obvious implications" for pf 4.5 in FreeBSD
9.0?

I assumed that pf always evaluates nat and rdr rules before filtering,
meaning that a nat rule placed after a pass/block rule would still be
executed first for outgoing packets. If so, the ordering shouldn't
really matter. Is that incorrect?

- Max