title: Dart polymer paper element - how to set attributes (dismissive and affirmative)
body: <p>I am trying this:  </p>
  
  
  
  <pre class="lang-dart prettyprint-override"><code>PaperButton pbOK = new PaperButton();
  pbOK.innerHtml="OK";
  pbOK.attributes={"affirmative":"xxxxx"};//wrong of course..??
  </code></pre>
  
  <p>which is Dart compiler-legal, but is incorrect.<br>
  What should it be please?</p>