code: public void addHole( Polygon poly )
      {
          if( _holes == null )
          {
              _holes = new ArrayList<Polygon>();
          }
          _holes.add( poly );
          // XXX: tests could be made here to be sure it is fully inside
  //        addSubtraction( poly.getPoints() );
      }
docs: Assumes: that given polygon is fully inside the current polygon
  @param poly - a subtraction polygon