docs: function(shared) {
              var polygons = this.polygons.map(function(p) {
                  return new CSG.Polygon(p.vertices, shared, p.plane);
              });
              var result = CSG.fromPolygons(polygons);
              result.properties = this.properties; // keep original properties
              result.isRetesselated = this.isRetesselated;
              result.isCanonicalized = this.isCanonicalized;
              return result;
          }