title: Can an HTML element have the same attribute twice?
body: <p>I'm considering writing code which produces an HTML tag that could have duplicate attributes, like this:</p>
  
  <pre><code>&lt;div data-foo="bar" class="some-class" data-foo="baz"&gt;
  </code></pre>
  
  <p>Is this legal HTML? Does one of the <code>data-foo</code>-values take precendence over the other? Can I count on semi-modern browsers (IE >= 9) to parse it without choking?</p>
  
  <p>Or am I about to do something really stupid here?</p>