Hi Dave, instead of an HTML tag for viewports, there is an XML tag for it called <ViewPanel> in the very top level MainWindowLayout.xml file.

It can be a bit difficult to control the very top level window layout in HTML, so there is a custom layout mechanism to handle the particular needs of that. The view panel gets arranged with that layout mechanism rather than being embedded within an HTML panel.

I do intend to set up something in the future to allow for creating additional Top-level windows that have their own XML defined layouts, which could then specify view panels or HTML UI panels within them. That's the part that would allow for creating a second frame window with an additional set of viewports in it.

- Michael