code: private ProtoNetwork stage5(final Document document) {
          beginStage(PHASE1_STAGE5_HDR, "5", NUM_PHASES);
          final StringBuilder bldr = new StringBuilder();
  
          bldr.append("Building proto-network for ");
          bldr.append(document.getName());
          stageOutput(bldr.toString());
  
          long t1 = currentTimeMillis();
          ProtoNetwork ret = p1.stage5Building(document);
          long t2 = currentTimeMillis();
  
          bldr.setLength(0);
          markTime(bldr, t1, t2);
          markEndStage(bldr);
          stageOutput(bldr.toString());
  
          return ret;
      }
docs: Stage five build of proto-network.
  
  @param document BEL common document