code: private void addFirstChildElements() {
  		for (Node node : nodes) {
  			Index index = helper.getIndexInParent(node, false);
  			if (index.index == 0)
  				result.add(node);
  		}
  	}
docs: Add {@code :first-child} elements.
  
  @see <a href="http://www.w3.org/TR/css3-selectors/#first-child-pseudo"><code>:first-child</code> pseudo-class</a>