title: Passing down Polymer's HTML attributes to nested components
body: <p>I have a custom element <code>&lt;x-marker&gt;</code> with a <code>&lt;paper-checkbox&gt;</code> inside of it.</p>
  
  <p>I want an <code>checked</code> attribute on my element to reflect down on the <code>&lt;paper-checkbox&gt;</code> but my solution doesn't seem to be the way to do it.</p>
  
  <p>HTML:</p>
  
  <pre><code>&lt;x-marker is-checked="&lt;%= someBoolean %&gt;"&gt;&lt;/x-marker&gt;
  </code></pre>
  
  <p>Element:</p>
  
  <pre><code>&lt;dom-module id="x-marker"&gt;
  
    &lt;template&gt;
      &lt;div&gt;
        &lt;paper-checkbox id="checkbox"&gt;&lt;/paper-checkbox&gt;
      &lt;/div&gt;
    &lt;/template&gt;
  
    &lt;script&gt;
      Polymer({
        is: 'x-marker',
  
        properties: {
          isChecked: String
        },
  
        listeners: {
          change: 'changeHandler'
        },
  
        attached: function() {
          if (this.isChecked === 'true') {
            this.$.checkbox.setAttribute('checked', this.isChecked);
          }
        },
  
        changeHandler: function (event, detail, sender) {
          //...
        }
      });
    &lt;/script&gt;
  
  &lt;/dom-module&gt;
  </code></pre>
  
  <p>In Polymer 0.5 you could use <code>checked?="{{isChecked}}"</code>, but that doesn't seem to work in 1.0 anymore. Also hard coding <code>&lt;paper-checkbox checked="false"&gt;</code> still <em>checks</em> the checkbox as long as the attribute is present. The value doesn't seem to matter, that's why the attribute itself has to be bound, and not its value.</p>
  
  <p>I can't seem to figure this out, including treating the property as a string <code>=== 'true'</code> instead of a boolean, and bind it straight to the <code>&lt;paper-checkbox&gt;</code></p>