title: What does class="active" really do in bootstrap 3?
body: <p>I am learning twitter bootstrap 3 these days.
  There is a class called "active" in bootstrap. I have seen this feature even in CSS. As I know it indicates the active page or link (probably it is the page that we are currently in). Please correct me if I am wrong. What I need to know is why we need to call such a class in our mark-up. Because it is upto the user to decide which page that he needs to be in.</p>
  
  <p>If I explain this further below mark-up has used class="active" in the 2nd list element. (i.e Profile). When I run the code in a browser it adds a nice blue background to Profile. <strong>Why should I add such a class? Active tabs vary when users navigate from one tab to another. Is not it?</strong></p>
  
  <pre><code>&lt;div class="container"&gt;
              &lt;div class="row"&gt;
                  &lt;nav&gt;
                      &lt;ul class="nav nav-pills nav-justified"&gt;
                          &lt;li&gt;&lt;a href="Breadcrumbs.html"&gt;Dashboard&lt;/a&gt;&lt;/li&gt;
                          &lt;li class="active"&gt;&lt;a href="Jumbotron.html"&gt;Profile&lt;/a&gt;&lt;/li&gt;
                          &lt;li&gt;&lt;a href="FavoutieActors.html"&gt;Earnings&lt;/a&gt;&lt;/li&gt;
                          &lt;li&gt;&lt;a href="Buttons.html"&gt;Settings&lt;/a&gt;&lt;/li&gt;                        
                      &lt;/ul&gt;
                  &lt;/nav&gt;
              &lt;/div&gt;
          &lt;/div&gt;
  </code></pre>