public void onCheckChange(TreeNode<M> node, boolean checkable, CheckState state) {
Element checkEl = (Element) getCheckElement(node);
if (checkEl != null) {
node.setCheckElement(tree.getAppearance().onCheckChange(getElement(node),
checkEl.<XElement> cast(), checkable, state));
}
}
public void onDropChange(TreeNode<M> node, boolean drop) {
XElement e = tree.getView().getElementContainer(node);