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