What determines the Class? A, C, Super C, B, B+, confused

Class A is a "bus style" motorhome.
Class B is a cargo van style, without a cab over feature. Class B's are usually on a regular van frame, though sometimes they are an extended frame.
Class B+ is on a larger frame than a B, but still smaller than a C. They still don't have the cab over feature.
Class C is built on a van chassis, but with a much longer frame and a cab over feature.
Super C is built on a truck chassis (think Freightliner, not F-150) and are much beefier than a regular class C.