Here is the method I employed
<li>
<ul>
<li>Father</li>
<li>Mother</li>
</ul>
<a href="http://www.clarkeology.com/names/clarke/21/james">James CLARKE1779 - 1860</a>
<div itemprop="spouse">
<a href="http://www.clarkeology.com/names/cole/19/elizabeth">Elizabeth COLE 1794 - 1865</a>
</div>
<ol>
<li><a>Child</a></li>
<li><a>Child</a></li>
<li><a>Child</a></li>
</ol>
</li>
In this setup, any <li>
within the structure can repeat in a similar manner (though adding both children and parents to all may cause confusion... usually just add one or the other beyond the main individual in focus.
You can find a practical demonstration on with detailed css at /css/_tree.css, and the script used to interpret a GEDCOM file and generate the required html code at https://github.com/pauly/js-gedcom
I utilized itemprop
instead of class
above to integrate schema.org microformats into my project as well, although using class would serve the same purpose.
I was particularly impressed by the original css design I came across recently, and working on this has been quite enjoyable. Feel free to submit pull requests for my code!