public void readExternal(Element element) throws InvalidDataException {
   List<Element> subPanes = element.getChildren(ELEMENT_SUBPANE);
   for (Element subPane : subPanes) {
     String subId = subPane.getAttributeValue(ATTRIBUTE_SUBID);
     TreeState treeState = new TreeState();
     treeState.readExternal(subPane);
     myReadTreeState.put(subId, treeState);
   }
 }