For fifty years I have seen door manufacturers glue the four parts of a door, flat surface to flat surface. No matter how many coats of paint we apply to them they always form a gap at the joints of exterior exposure doors. This guy solved the problem and he doesn't even know it. Laser cut this wonderful joinery with a computer then glue it together with Gorilla Glue and it forms a permanent bond that will never separate and form a gap at the joints like conventional door manufacturing does.