code: private void addNthChild() {
          for (Node node : nodes) {
              int count = 1;
              Node n = DOMHelper.getPreviousSiblingElement(node);
              while (n != null) {
                  count++;
                  n = DOMHelper.getPreviousSiblingElement(n);
              }
              
              if (specifier.isMatch(count)) {
                  result.add(node);
              }
          }
      }
docs: Add the {@code :nth-child} elements.
  
  @see <a href="http://www.w3.org/TR/css3-selectors/#nth-child-pseudo"><code>:nth-child</code> pseudo-class</a>