How do I open a TabPanel within my MDI Window where I can add multiple items found in some of the viewport or layout examples? I followed the example found here https://examples1.ext.net/#/XRender/Basic/Add_Items/ and while I can add a new tab with some simple html, how I can I add a left and right panel sitting on top of a bottom panel? Do I have to create a separate form for that? If so, how I can send a menu command to a form sitting in an iframe? Users hits the save button on the toolbar and that commands gets passed to the iframe form.

Thanks in advance.