Hello. I have a mainwindow, I want 3 dockwidget (dw1 dw2 & dw3)
I want dw3 to span entire bottom and dw1 & dw2 to split remainder of
window horizontally, what Dockarea do I set for dw1 & dw2? I dont use
any of the space for central widget. If dw1 is undocked, dw2 should fill
all space above dw3, and if dw2 is undocked, dw1 should remain same
size and uncovered centralwidget space should remain empty of other
widgets.

addDockWidget(Qt::BottomDockWidgetArea,dw3);
addDockWidget(Qt::???, dw1);
addDockWidget(Qt::???, dw2);;