title: Disable navigation item
body: <p>I want to disable my navigation item using this code:</p>
  
  <pre><code>md-nav-bar
      md-nav-item A
      md-nav-item(ng-disabled=false) B
  </code></pre>
  
  <p>However, it doesn't work. Looking for the docs but couldn't find anything. How to disable navigation item in correct way?</p>