title: Polymer paper-checkbox properties
body: <p>I am trying to create a register page using pure polymer. I used a paper-checkbox to let user check and agree the term of use. And my intention was only to display the submit button, (paper-button ) if the user has checked the user agreement. I am just wondering if there is a way that I can accomplish this using pure polymer instead of java script. I know paper-checkbox has a boolean property called "checked". I figure it would be nice that I could access this property inside my submit button and disable the button if checked is false.</p>
  
  <p>Here is what I have, but it does not work</p>
  
  <pre><code>&lt;paper-checkbox id="checkbox" checked$="{{ checked }}"&gt; I agree user terms
  &lt;/paper-checkbox&gt;
  &lt;paper-button raised disabled$="{{ checked }}" onclick="submitForm()"&gt;Create  
  ID&lt;/paper-button&gt;
  </code></pre>