The draw functions inside the DrawScreenspace class (and some functions from other classes like "DrawText.WriteScreenspace()") have overloads that don't specify the camera whose screenspace should be used for drawing. When drawing with these overloads then it is first checked whether defaultCameraForDrawing is assigned. If it is not assigned then a camera for drawing is automatically searched, and this "defaultScreenspaceWindowForDrawing" setting here decides where to search first. It can be the Game View window or the Scene View Window.