This is useful for letting mechanisms convey information which may be
useful in making a decision whether an action is OK. For example,
NetworkManager could use this to provide the phone-number parameter
with a hypothetical "nm-dialup" action. Then a site or vendor can
provide insert

 mandatory polkit-run-program.so program="/usr/lib/check-dialup-number.sh" privilege="nm-dialup"

into /etc/PolicyKit/PolicyKit.conf and have said program check

 $POLKIT_ACTION_PARAM_PHONE_NUMBER

in that program.