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/BasicPackageImpl.java
* @generated
	 * @ordered
	 */
	public static final int PART_SASH_CONTAINER__ELEMENT_ID = UiPackageImpl.GENERIC_TILE__ELEMENT_ID;
	/**
	 * The feature id for the '<em><b>Tags</b></em>' attribute list.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	public static final int PART_SASH_CONTAINER__TAGS = UiPackageImpl.GENERIC_TILE__TAGS;
	/**
	 * The feature id for the '<em><b>Widget</b></em>' attribute.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	public static final int PART_SASH_CONTAINER__WIDGET = UiPackageImpl.GENERIC_TILE__WIDGET;
	/**
	 * The feature id for the '<em><b>Renderer</b></em>' attribute.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	public static final int PART_SASH_CONTAINER__RENDERER = UiPackageImpl.GENERIC_TILE__RENDERER;
	/**
	 * The feature id for the '<em><b>To Be Rendered</b></em>' attribute.