Story #69712: Further FormEngine development
The "tabbing" in FormEngine is currently done at various (i think container only) places with methods getDynamicTabMenu() and getDynTabMenuId() from DocumentTemplate.
This should be inlined to FormEngine code, probably via method(s) located within AbstractContainer.
It might be a good idea to work on an own template for that, so maybe the ones currently referenced in getDynamicTabMenu could be copied to a location where that is only used by FormEngine.
One important thing is that the existing $this->pageRenderer->loadRequireModule() call vanishes and instead is added to "requireJsModules" of $resultArray: No render element must call pageRenderer directly or inderectly, ever.