At joint suggestion between Jesse + Jarda:

/** This method allows DataFolder to filter its nodes.
 *
 * @param filter filter for subdata objects
 * @return the node delegate (without parent) for this data object
 */
 final Node getClonedNodeDelegate (DataFilter filter) {
   // [PENDING] or use .class()==FolderNode.class?
   if (getNodeDelegate () instanceof FolderNode) {
     // creates normal node and filters its children
     return new ClonedFilter (filter);
   } else {
     return getNodeDelegate ().cloneNode ();
   }
 }

Should make it nicer to subclass DataFolder + FolderNode.

Also CC George.Fink@eng.sun.com.