title: Update template variable using setAttribute/property
body: <p>In my Polymer Element, I have a binding defined using the mustache syntax, e.g. <code>&lt;input value="{{nick}}"&gt;</code>.</p>
  
  <p>I would like to update the value of that input as well as the bound <code>nick</code> template variable using regular DOM operations, such as <code>nickInput.setAttribute("value", newVal)</code> or <code>nickInput.value = newVal</code> but neither works. </p>
  
  <p>Is there a way to achieve this?</p>
  
  <p>Demo: <a href="http://jsfiddle.net/warpech/nvbwqqqx/" rel="nofollow">http://jsfiddle.net/warpech/nvbwqqqx/</a> </p>