The log filter:
class=oper | class="trace" & severity>10
will be evaluated as:
(class=oper) or (class=trace and severity>10)
and will log all operational messages plus trace messages with severity higher than 10.
If no log filter is given, the default filter is:
class=oper | class="audit" | class="billing"
To exclude certain classes of messages, a filter like this can be used:
! class = trace & ! class = profile