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.edit/src/org/eclipse/e4/ui/model/application/ui/basic/provider/BasicItemProviderAdapterFactory.java
/**
	 * This keeps track of the one adapter used for all {@link org.eclipse.e4.ui.model.application.ui.basic.MStackElement} instances.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	protected StackElementItemProvider stackElementItemProvider;
	/**
	 * This creates an adapter for a {@link org.eclipse.e4.ui.model.application.ui.basic.MStackElement}.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	@Override
	public Adapter createStackElementAdapter() {
		if (stackElementItemProvider == null) {
			stackElementItemProvider = new StackElementItemProvider(this);
		}
		return stackElementItemProvider;
	}
	/**
	 * This returns the root adapter factory that contains this factory.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 */
	public ComposeableAdapterFactory getRootAdapterFactory() {
		return parentAdapterFactory == null ? this : parentAdapterFactory.getRootAdapterFactory();
	}
	/**