we used the following expression within a settings file
Filter="%_% & %_% contains extraordinary"
In case we do this, the corresponding sink doesn't emit any messages. It seems that "%_%" is not replaced by the message.
As you said, the message has not been realized using the attributes mechanism so it's not accessible as an attribute. On the other hand when defining a Formatter we can make use of the special expression "%_%". Is it possible to extend the filter mechanism to gain access to the message (within the settings file) ?
Filtering cannot be applied to log messages because message does not exist when the filter is applied. The filter you specified effectively looks for an attribute with name "_" and most probably doesn't find it.
Oh yes, I remember the part in the documentation about method open_record checking whether or not any of the sinks is interested in the record. The obviously excludes including the message in any filtering expression…
Sorry for the unnecessary noise.