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
public EClass getWindow() {
		return windowEClass;
	}
	/**
	 * Returns the meta object for the containment reference '{@link org.eclipse.e4.ui.model.application.ui.basic.MWindow#getMainMenu <em>Main Menu</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for the containment reference '<em>Main Menu</em>'.
	 * @see org.eclipse.e4.ui.model.application.ui.basic.MWindow#getMainMenu()
	 * @see #getWindow()
	 * @generated
	 */
	public EReference getWindow_MainMenu() {
		return (EReference)windowEClass.getEStructuralFeatures().get(0);
	}
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.e4.ui.model.application.ui.basic.MWindow#getX <em>X</em>}'.
	 * <!-- begin-user-doc -->
	 * <!-- end-user-doc -->
	 * @return the meta object for the attribute '<em>X</em>'.
	 * @see org.eclipse.e4.ui.model.application.ui.basic.MWindow#getX()
	 * @see #getWindow()
	 * @generated
	 */
	public EAttribute getWindow_X() {
		return (EAttribute)windowEClass.getEStructuralFeatures().get(1);
	}
	/**
	 * Returns the meta object for the attribute '{@link org.eclipse.e4.ui.model.application.ui.basic.MWindow#getY <em>Y</em>}'.
	 * <!-- begin-user-doc -->