This trigger expression works as follows:
1. It can be triggered if the operations status is down.
2. Use $IFCONTROL macro with context "{#IFNAME}" to void trigger firing on specific interfaces. Values:
-  0 : Marks an interface as not important. Trigger does not fire when interface is down.
-  1 : Default value to fire the trigger when interface is down
3. change(//net.if.status[{#IFNAME}]) - condition prevents firing of trigger if status did not change. It helps in cases, when interfaces were initially down.
BEWARE, manual close will ceasefire until at least two status changes happens again!