This works great as all the controls in the box appear, but the
boxView expands to take up the full frame of the selectedTabViewItem.
This is a problem because I want to use the different between the
boxView and the selectedTabViewItem to resize the window, thus
preventing a lot of empty space in the window.
I've tried setting autoResizeMask to NSViewNotSizable, and turned off
all the automatic sizing options in IB, but the box still expands.