CreateBehindHookLayer(li,bm,x0,y0,x1,y1,flags,hook,bm2)
                                         (a0/a1,d0/d1/d2/d3/d4/a3,a2)
                                        - Create a new layer behind all
                                          existing layers.
CreateUpfrontHookLayer(li,bm,x0,y0,x1,y1,flags,hook,bm2)
                                         (a0/a1,d0/d1/d2/d3/d4/a3,a2)
                                        - Create a new layer on top of
                                          existing layers.
InstallLayerHook(layer,hook)(a0/a1)     - Safely install a new
                                          Layer->BackFill hook.
MoveSizeLayer(layer,dx,dy,dw,dh)(a0,d0/d1/d2/d3)
                                        - Position/Size layer