title: Multiple viewports in ToggleWindow
body: <p>I have a toggle window (with <code>2D</code> graphic) with several <code>Viewports</code>. How do I now which <code>Viewport</code> that is active? Is there an <code>API</code> where I can get access to the <code>Viewports</code>? I haven't found any documentation about this.</p>