drools-distribution-6.0.0.Final/reference_manual/html/ch06.html#d0e3594

 or on the net:

As you can see it references the .rf style.  Also the way that it is laid out has rule flow groups.  The idea is that name corresponds to the rule flow group noted in the Rule file (drl).  In the Drools 6.0 plugin, there is no rule-flow icon, only start event, end event, rule task, etc.