title: Can I set a (valid) empty src on an audio source tag?
body: <p>I'm setting up a website, and want to create an HTML5 audio player, but inject the source later on with JavaScript. I have prepared the following HTML:</p>
  
  <pre><code>&lt;audio id=show&gt;
      &lt;source id=oggFile type=audio/ogg /&gt;
      &lt;source id=mp3File type=audio/mpeg /&gt;
  &lt;/audio&gt;
  </code></pre>
  
  <p>Unfortunately, the W3C validator is panning my code, claiming <code>src</code> is a required attribute. Due to the way collateral code interacts with the player, I would strongly prefer not having this set to a valid audio file. I have for testing set the <code>src</code> to a dummy file...</p>
  
  <pre><code>&lt;audio id=show&gt;
      &lt;source id=oggFile src=/audio/does-not-exist.ogg type=audio/ogg /&gt;
      &lt;source id=mp3File src=/audio/does-not-exist.mp3 type=audio/mpeg /&gt;
  &lt;/audio&gt;
  </code></pre>
  
  <p>...but I'm not sure this is the best approach, and, in Firefox at least, it throws up warnings in the console.</p>
  
  <p>Is there a way I can set an effectively-blank <code>src</code> attribute that still validates?</p>