This trigger expression works as follows:
1. It can be triggered if the health check state is dead.
2. `{$SDWAN.HEALTH.IF.CONTROL:"{#HNAME}"}=1` - a user can redefine the context macro to "0", marking this health check as not important. No new trigger will be fired if this health check is dead.
3. `{TEMPLATE_NAME:METRIC.diff()}=1` - the trigger fires only if the health check state was up to "1" sometime before.

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