title: When is a closing </li> not optional?
body: <p><a href="http://www.w3.org/TR/html-markup/li.html" rel="noreferrer">W3 says</a>:</p>
  
  <blockquote>
    <p>An <code>li</code> element’s end tag may be omitted if the <code>li</code> element is immediately followed by another <code>li</code> element or if there is no more content in the parent element.</p>
  </blockquote>
  
  <p>But this:</p>
  
  <pre><code>&lt;ol&gt;
      &lt;li&gt;one
      &lt;li&gt;two
      &lt;li&gt;three
          &lt;ol&gt;
              &lt;li&gt;three.one
              &lt;li&gt;three.two
          &lt;/ol&gt;
      &lt;li&gt;four
  &lt;/ol&gt;
  </code></pre>
  
  <p>Appears to <a href="http://jsfiddle.net/yt94J/" rel="noreferrer">render fine</a>.</p>
  
  <p>I don't know if four's <code>li</code> is considered to "immediately follow" three's <code>li</code> or not because there's an <code>ol</code> inbetween. The spec isn't really clear -- technically the text "one" represents a TextNode so two's <code>li</code> doesn't really immediately follow either.</p>
  
  <p>Is there <em>actually</em> any scenario where a closing <code>&lt;/li&gt;</code> is necessary? </p>
  
  <p>I've only got Chrome and Firefox installed, but they both render the above how I would expect.</p>
  
  <p>As far as I'm aware, the only legal direct children of <code>ul</code> and <code>ol</code> are <code>li</code> so there <em>can't</em> be any ambiguity, right?</p>