These changes are designed to enhance the rendering of surfaces that come from unstructured grids that have quadratic cells.  Whereas before every quadratic face was tessellated on the control points, these changes allow you to select a subdivision level in vtkDataSetSurfacefilter used to convert the quadratic faces to approximating linear polygons.

There has also been some support added for rendering correct wireframes from the extracted surface.  This includes changing the painters to support a new vtkDataSetAttributes::EDGEFLAG that hides the internal edges of the approximating polygons.