code: private void addDescendantElements() throws NodeSelectorException {
          for (Node node : nodes) {
              List<Node> nl;
              if (node instanceof Document || node instanceof Element) {
                  nl = DOMHelper.getElementsByTagName(node, selector.getTagName());
              } else {
                  throw new NodeSelectorException("Only document and element nodes allowed!");
              }
              
              result.addAll(nl);
          }
      }
docs: Add descendant elements.
  
  @see <a href="http://www.w3.org/TR/css3-selectors/#descendant-combinators">Descendant combinator</a>
  
  @throws NodeSelectorException If one of the nodes have an illegal type.