While texture mapping is done via box projection based on the plane itself, the actual texture mapping parameters are separate values than the plane (specifical

While texture mapping is done via box projection based on the plane itself, the actual texture mapping parameters are separate values than the plane (specifically they are scaling, shifting and rotation). Some .map extensions do store vectors instead of scale/shift/rotate that allow much more flexible texture mapping (though still need to be on a plane, but can represent things like skewing), but these are still stored separately from the plane.