title: Why is e.parameter.source undefined?
body: <p>I am trying to find out where a callback function came from, but <code>e.parameter.source</code> has been undefined. </p>
  
  <p>The code I'me using to create the callback event is:</p>
  
  <pre><code>var temp_handler = app.createServerHandler("do_things");
  container.add(app.createButton(s_list[i][2]).setId("goto_"+s_list[i][1]).addClickHandler(temp_handler));
  container.add(app.createLabel("goto_"+s_list[i][1]));
  </code></pre>
  
  <p>where <code>container</code> is later added to the app.</p>
  
  <p>The first part of the function that gets called is:</p>
  
  <pre><code>function do_things (e)
  {
    var app = UiApp.getActiveApplication();
    Logger.log(e.parameter);
    var src = e.parameter.source;
  </code></pre>
  
  <p>From this, I have been able to tell that <code>e.parameter</code> is:</p>
  
  <pre><code>{clientY=61, clientX=38, button=1, alt=false, eventType=click, screenY=278, ctrl=false, screenX=493, y=11, shift=false, meta=false, x=34}
  </code></pre>
  
  <p>This does not include <code>source</code>. I find this peculiar because as far as I can tell, other callback functions in the same file have been able to access and use <code>e.parameter.source</code> without issue. </p>
  
  <p>Does anyone know what I am doing wrong in this callback such that the source parameter is inaccessible?</p>