This trigger expression works as follows:
1. It can be triggered if the operations status is down.
2. `{$IFCONTROL:"{#IFNAME}"}=1` - a user can redefine the context macro to "0", marking this interface as not important.
No new trigger will be fired if this interface is down.
3. `last(/TEMPLATE_NAME/METRIC,#1)<>last(/TEMPLATE_NAME/METRIC,#2)` - the trigger fires only if the operational status was up to (1) sometime before (so, does not fire for the 'eternal off' interfaces.)

WARNING: if closed manually - it will not fire again on the next poll, because of .diff.