Bug 317405 [Model] HandledItem should be abstract
Looks like an oversight the only real types are HandledMenuItem and HandledToolItem.
bundles/org.eclipse.e4.ui.model.workbench.edit/src/org/eclipse/e4/ui/model/application/ui/advanced/provider/PerspectiveStackItemProvider.java
(createChildParameter
				(UiPackageImpl.Literals.ELEMENT_CONTAINER__CHILDREN,
				 MMenuFactory.INSTANCE.createRenderedMenu()));
		newChildDescriptors.add
			(createChildParameter
				(UiPackageImpl.Literals.ELEMENT_CONTAINER__CHILDREN,
				 MMenuFactory.INSTANCE.createRenderedToolBar()));
		newChildDescriptors.add
			(createChildParameter
				(UiPackageImpl.Literals.ELEMENT_CONTAINER__CHILDREN,
				 MMenuFactory.INSTANCE.createToolBarContribution()));
		newChildDescriptors.add
			(createChildParameter
				(UiPackageImpl.Literals.ELEMENT_CONTAINER__CHILDREN,
				 MMenuFactory.INSTANCE.createTrimContribution()));
		newChildDescriptors.add
			(createChildParameter
				(UiPackageImpl.Literals.ELEMENT_CONTAINER__CHILDREN,
				 MBasicFactory.INSTANCE.createPart()));
		newChildDescriptors.add
			(createChildParameter
				(UiPackageImpl.Literals.ELEMENT_CONTAINER__CHILDREN,
				 MBasicFactory.INSTANCE.createInputPart()));
		newChildDescriptors.add
			(createChildParameter
				(UiPackageImpl.Literals.ELEMENT_CONTAINER__CHILDREN,
				 MBasicFactory.INSTANCE.createPartStack()));
		newChildDescriptors.add
			(createChildParameter
				(UiPackageImpl.Literals.ELEMENT_CONTAINER__CHILDREN,