Log4j provides the option to specify marker for each individual log entry. The behaviour of these Markers can be specified in log4j config file. There is a lot what log4j can do to marked entries: hide from all and-or selected loggers, forward, encrypt, reformat etc.

Since the log4j config file is located in odlparent/karaf/opendaylight-karaf-resources/src/main/resources/etc/org.ops4j.pax.logging.cfg it is only logical to create odlparent artifact which will provide the Markers to all child ODL projects so the marking is consistent.