code: public void add(XmlReader node)
      {
          Check.notNull(node);
  
          final Element element = node.getElement();
          document.adoptNode(element);
          root.appendChild(element);
      }
docs: Add a child node.
  
  @param node The child node@throws LionEngineException If invalid argument.
  @throws LionEngineException If error when adding the node.