   If the browser location changes to `/foo`, the markup changes to this:
 
       <nav>
-        <a href="/foo" up-current>Foo</a>
+        <a href="/foo" class="up-current">Foo</a>
         <a href="/bar">Bar</a>
       </nav>
 


      <a href="/reports" up-alias="/reports/*">Reports</a>

  @selector [up-current]
  @stable
  ###
  up.on 'up:fragment:inserted', ->

  The user clicks on the link. While the request is loading,
  the link has the `up-active` class:

      <a href="/foo" up-follow class="up-active">Foo</a>

  Once the link destination has loaded and rendered, the `up-active` class
  is removed and the [`up-current`](/up-current) class is added:

      <a href="/foo" up-follow class="up-current">Foo</a>

  @selector .up-active
  @stable
  ###
  sectionClicked = ($section) ->
