Test your skills further by creating your own split view controller. Use an ordinary NSView and not NSSplitView – you will do the view arranging yourself in the view controller. Keep it simple for now: assume there will only be two child view controllers and always vertically or horizontally split. As NSSplitViewController does, create a pane for each child view controller. Use Auto Layout to set the width of the panes to be equal. Do not worry about the draggable divider for now.