/** starts a block in which nested nodes can be created.
* This block can be ended with {@link #compositeEnd()}.
* A current node is required. */
public ProcessFactory compositeNode(String nodeName) {
if (exceptionHandler!=null) {
throw new PvmException("exceptionHandler needs to be closed with exceptionHandlerEnd");
}
if (compositeElementStack==null) {
compositeElementStack = new Stack<CompositeElementImpl>();
}