Bug 317417 [Model] StackElement should be abstract and interface
StackElement is only a marker for improved containment hierarchies. We should at least make it abstract but also as an interface like WindowElement, ...
bundles/org.eclipse.e4.ui.model.workbench/src/org/eclipse/e4/ui/model/application/ui/basic/impl/BasicFactoryImpl.java
* Creates an instance of the factory.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	public BasicFactoryImpl() {
		super();
	}
	/**
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	@Override
	public EObject create(EClass eClass) {
		switch (eClass.getClassifierID()) {
			case BasicPackageImpl.PART: return (EObject)createPart();
			case BasicPackageImpl.INPUT_PART: return (EObject)createInputPart();
			case BasicPackageImpl.PART_STACK: return (EObject)createPartStack();
			case BasicPackageImpl.PART_SASH_CONTAINER: return (EObject)createPartSashContainer();
			case BasicPackageImpl.WINDOW: return (EObject)createWindow();
			case BasicPackageImpl.TRIMMED_WINDOW: return (EObject)createTrimmedWindow();
			case BasicPackageImpl.TRIM_BAR: return (EObject)createTrimBar();
			case BasicPackageImpl.STACK_ELEMENT: return (EObject)createStackElement();
			default:
				throw new IllegalArgumentException("The class '" + eClass.getName() + "' is not a valid classifier"); 
		}
	}
	/**
	 * <!-- begin-user-doc -->