title: What's the purpose of separate navbar and navbar-inner classes?
body: <p>In Twitter bootstrap's starter-template.html, the navbar is written as</p>
  
  <pre><code>&lt;div class="navbar"&gt;
    &lt;div class="navbar-inner"&gt;
      &lt;div class="container"&gt;
      ...
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>However, if I change the markup to </p>
  
  <pre><code>&lt;div class="navbar navbar-inner"&gt;
    &lt;div class="container"&gt;
    ...
    &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>everything seems to work fine and there's no discernible visual differences as far as I can tell. What's the reason to have separate <code>navbar</code> and <code>navbar-inner</code> classes associated with two divs? Why not just have a <code>navbar</code> class that combines styles of both?</p>