title: How to evalute code in the chain or pretend callback function?
body: <p>I dynamically add an image on my page :</p>
  
  <pre><code>&lt;div class="simple_overlay" id="overlay"&gt;
     &lt;img src="" /&gt;
  &lt;/div&gt;
  
  &lt;script type="text/javascript"&gt;
  $(function() {
      $("a[rel]").overlay({
          var source = this.getTrigger().attr('href');
          this.getOverlay().find("img").attr({'src': source});
      });
  });
  &lt;/script&gt;
  </code></pre>
  
  <p>Now, I need to get width of the new image and calculate <code>margin-left</code> corresponding to it. Native jQuery Tools methods doesn't work, because when overlay is loading, image hasn't yet loaded and container <code>#overlay</code> width is 0.
  Is there any option to emulate callback on this chain, so i can use <code>width()</code> right after <code>attr()</code> has evaluated?</p>