Quick note: if you're trying to find out what's going on with your BPATH statement and you want to debug the traversal thereof, the central entrypoint is method CL_WCF_BPATH_PARSER=>STATUSMACHINE. This splits the string and acts on the segments.
Method CL_WCF_BPATH_PARSER=>PROCESS_ACTION is then called to delegate processing of the different segment types to different methods.
Finally, CL_WCF_BPATH_PARSER=>PROCESS_RELATION is called to process relations. Here, line 59 calls a method that calls the get_related_entities method of the BOL entity, which brings us back to standard BOL.
