Check -> [url removed, login to view]
Now click on tab 4, or 5.
As you can see, there are no "subtabs" there.
Tabs 4 and 5 were added calling the already done "AddTab" function at the end of the page.
All you have to do is a function to add the "SUB" tab there.
After that a RemoveSubTab should be called to to remove the dynamic subtab you added what wouldn't be a problem.
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This should be a clean JS (jQuery) solution. I've done this things many times, and it shouldn't be any problems. Please contact me to discuss this issue further.