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/basic/provider/WindowItemProvider.java
(createChildParameter
				(BasicPackageImpl.Literals.WINDOW__WINDOWS,
				 MBasicFactory.INSTANCE.createTrimmedWindow()));
		newChildDescriptors.add
			(createChildParameter
				(BasicPackageImpl.Literals.WINDOW__SHARED_ELEMENTS,
				 MBasicFactory.INSTANCE.createPart()));
		newChildDescriptors.add
			(createChildParameter
				(BasicPackageImpl.Literals.WINDOW__SHARED_ELEMENTS,
				 MBasicFactory.INSTANCE.createInputPart()));
		newChildDescriptors.add
			(createChildParameter
				(BasicPackageImpl.Literals.WINDOW__SHARED_ELEMENTS,
				 MBasicFactory.INSTANCE.createPartStack()));
		newChildDescriptors.add
			(createChildParameter
				(BasicPackageImpl.Literals.WINDOW__SHARED_ELEMENTS,
				 MBasicFactory.INSTANCE.createPartSashContainer()));
		newChildDescriptors.add
			(createChildParameter
				(BasicPackageImpl.Literals.WINDOW__SHARED_ELEMENTS,
				 MBasicFactory.INSTANCE.createWindow()));
		newChildDescriptors.add
			(createChildParameter
				(BasicPackageImpl.Literals.WINDOW__SHARED_ELEMENTS,
				 MBasicFactory.INSTANCE.createTrimmedWindow()));
		newChildDescriptors.add
			(createChildParameter
				(BasicPackageImpl.Literals.WINDOW__SHARED_ELEMENTS,