Bug 327933 Unrendering container with invalid selectedElement can cause target element to be unrendered
bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/PartRenderingEngine.java
if (factoryUrl == null) {
			factoryUrl = defaultFactoryUrl;
		}
		this.factoryUrl = factoryUrl;
	}
	protected void fixZOrder(MUIElement element) {
		MElementContainer<MUIElement> parent = element.getParent();
		if (parent == null || !(element.getWidget() instanceof Control))
			return;
		Control elementCtrl = (Control) element.getWidget();
		Control prevCtrl = null;
		for (MUIElement kid : parent.getChildren()) {
			if (kid == element) {
				if (prevCtrl != null)
					elementCtrl.moveBelow(prevCtrl);
				else
					elementCtrl.moveAbove(null);
				return;
			} else if (kid.getWidget() instanceof Control) {
				prevCtrl = (Control) kid.getWidget();
			}
		}
	}
	/**
	 * Initialize a part renderer from the extension point.
	 * 
	 * @param context
	 *            the context for the part factories
	 */
	@PostConstruct