code: protected void writeCombiner( TupleCombiner combiner)
      {
      writer_
        .element( COMBINE_TAG)
        .attribute( TUPLES_ATR, String.valueOf( combiner.getTupleSize()))
        .content( () ->
          {
          Arrays.stream( combiner.getIncluded())
            .sorted()
            .forEach( this::writeIncluded);
          
          Arrays.stream( combiner.getExcluded())
            .sorted()
            .forEach( this::writeExcluded);
  
          toStream( combiner.getOnceTuples()).forEach( this::writeOnceTuple);
          })
        .write();
      }
docs: Writes the given combiner definition.