Because you can make a subwindow .. or popup-window, if you prefer..
think of this:
app=CreateWindow("designer",0,0,640,480)
PaletteEditor=CreateWindow("edit palette",64,64,256,128,app)
think of this:
app=CreateWindow("designer",0,0,640,480)
PaletteEditor=CreateWindow("edit palette",64,64,256,128,app)