title: In the DOM are node ids case sensititve?
body: <p>Is this HTML valid?  Or is the id 'a' the same as the id 'A'?</p>
  
  <pre><code>&lt;div id="a"&gt;alpha&lt;/div&gt;
  &lt;div id="A"&gt;Alpha&lt;/div&gt;
  </code></pre>