title: How to set a component published attribute
body: <p>I have a dart-polymer component mediator-form that I would like to add programmatically to another component. That I have done successfully. However, mediator-form is used several times. For my purpose I would like to pass @published data in the form</p>
  <pre><code>&lt;mediator-form mediator='Medication'&gt;
  </code></pre>
  <p>where the published mediator data is used.</p>
  <p>My problem is I don't know how to set the mediator='Medication' programmatically.</p>
  <p>My attempt is shown below</p>
  <h2>.html</h2>
  <pre><code>  &lt;link rel='import' href='mediator_form.html'&gt;
  </code></pre>
  <h2>.dart</h2>
  <pre><code>  var newElem = new Element.tag('mediator-form')
      ..attributes['mediator'] = 'Medication';
  </code></pre>
  <p>does not work. newElement does not have a setProperty() method so it does not seem possible.</p>
  <p>Any help is appreciated. Thanks.</p>