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
/**
	 * The meta object id for the '{@link org.eclipse.e4.ui.model.application.ui.basic.impl.StackElementImpl <em>Stack Element</em>}' class.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @see org.eclipse.e4.ui.model.application.ui.basic.impl.StackElementImpl
	 * @see org.eclipse.e4.ui.model.application.ui.basic.impl.BasicPackageImpl#getStackElement()
	 * @generated
	 */
	public static final int STACK_ELEMENT = 10;
	/**
	 * The feature id for the '<em><b>Element Id</b></em>' attribute.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated
	 * @ordered
	 */
	public static final int STACK_ELEMENT__ELEMENT_ID = UiPackageImpl.UI_ELEMENT__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 STACK_ELEMENT__TAGS = UiPackageImpl.UI_ELEMENT__TAGS;
	/**
	 * The feature id for the '<em><b>Widget</b></em>' attribute.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @generated