title: Add a class to polymer element
body: <p>Everytime a checkbox inside my template is selected, I want to add a class to my polymer element or change polymer element's attribute. </p>
  
  <p>Since my element uses <code>label for</code> attribute, I bound the ID of the checkbox to when instantiating the element in my markup</p>
  
  <pre><code>&lt;label for="{{uniqueid}}" on-tap="{{toggle}}" /&gt;
    &lt;input type="checkbox" id="{{uniqueid}}" class="select" checked="{{checker}}"&gt;
    &lt;img src="{{image}}" alt="" class="prod-img"&gt;
    &lt;div class="grid-details"&gt;
      &lt;span&gt;{{designer}}&lt;/span&gt;
      &lt;span&gt;{{product}}&lt;/span&gt;
      &lt;span&gt;{{currency}} {{price}}&lt;/span&gt;
      &lt;span&gt;Shipped from {{info}}&lt;/span&gt;
    &lt;/div&gt;
  &lt;/label&gt;
  </code></pre>
  
  <p>I would then call the element like so </p>
  
  <pre><code>&lt;gmselect-element uniqueid="four" image="http://i.imgur.com/fkq1QKq.jpg" designer="CUCARELIQUIA" product="Castellano Suede Bag Redder" info="Gijon, Spain" price="650" currency="$"&gt;&lt;/gmselect-element&gt;
  </code></pre>
  
  <p>My toggle function looks like below </p>
  
  <pre><code>toggle: function() {
      this.$.grid.setAttribute("class", "grid true");
      this.setAttribute("selected", "true");
    }
  </code></pre>
  
  <p>However, instead of setting it to true here, I would like to check the value of the checkbox's checked property. Since ID is not static, I can't get element using the $ functionality. I also don't know how to escape a data bound in moustache's to get its value inside a method.</p>