title: What is attribute md-nav-sref of md-nav-item is used for?
body: <p>In below simple navigator bar example, there is a attribute called <code>md-nav-sref="some"</code>. Without that attribute, Angular doesn't display the navigator bar buttons. What is <code>md-nav-sref</code> used for? Is there anyway I can used <code>md-nav-sref</code> to change the content of <code>#show-this</code> <code>div</code> element?</p>
  
  <pre><code>&lt;md-nav-bar md-selected-nav-item="projectContentType"&gt;
    &lt;md-nav-item md-nav-sref="some" name="module-view"&gt;module view&lt;/md-nav-item&gt;
  &lt;/md-nav-bar&gt;
  &lt;div id="show-this"&gt; {{projectContentType}} &lt;/div&gt;
  </code></pre>