title: content attribute of img elements
body: <p>While inspecting the Chrome Dev tools, I noticed the following CSS fragment:</p>
  
  <pre><code>img {
      content: url(image-src.png);
  }
  </code></pre>
  
  <p>which works perfectly in Chrome (see Screenshot below).</p>
  
  <p><img src="https://i.stack.imgur.com/WMhbD.png" alt="Chrome Dev Tools"></p>
  
  <p>This allows me to define the src attribute of an &lt;img&gt; tag via CSS. Doesn't work in Firefox. Until now I thought that is not possible to directly modify the src attribute via css and I have not found anyone talking about this. <strong>So, is this just a proprietary addition in Chrome or is Chrome implementing a W3C draft or something comparable I am not aware of?</strong></p>