This trigger expression works as follows:
1. Can be triggered if operations status is down.
2. {$IFCONTROL:\\"{#IFNAME}\\"}=1 - user can redefine Context macro to value - 0. That marks this interface as not important.
    No new trigger will be fired if this interface is down.
3. {TEMPLATE_NAME:METRIC.diff()}=1) - trigger fires only if operational status is different from Connected(2).

WARNING: if closed manually - won't fire again on next poll, because of .diff.