openbsd5.3-beta, pf.conf, new keyword : once

[Wesley M.A.]

Hi,

I just see this in the pf.conf manpage:
once    Creates a one shot rule that will remove itself from an active
        ruleset after the first match.  In case this is the only rule 
in
        the anchor, the anchor will be destroyed automatically after 
the
        rule is matched.

It is a excellent feature, is it possible to have a example of use ?

Cheers,

Wesley.