I understand what you suggestion mean and it actually is very good suggestion, but in the case with the design of the widgets which are standalone controls this will not be possible. To achieve what you desire I have a partial solution creating custom layout controls
that can be used to nest multiple widgets.
I have attached a sample custom layout control with tabs that is showing in preview and rendering properly in preview. Please examine this approach which is different from the one mentioned in the forum and tell me if it works for you.
To register the control add App_Code folder and place the code file in it. The template can remain in the root folder.
To register the control
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