title: Reason for span tags in Bootstrap nav bar header
body: <p>I was learning bootstrap from w3schools. Please find the link.
  <a href="http://www.w3schools.com/bootstrap/tryit.asp?filename=trybs_navbar_collapse&amp;stacked=h" rel="nofollow">http://www.w3schools.com/bootstrap/tryit.asp?filename=trybs_navbar_collapse&amp;stacked=h</a></p>
  
  <p>In this link, in nav bar header I could notice the span tag as </p>
  
  <pre><code>&lt;span class="icon-bar"&gt;&lt;/span&gt;
  </code></pre>
  
  <p>it is used more than once in nav bar header. I removed those span tags from code.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  &lt;html lang="en"&gt;
  &lt;head&gt;
    &lt;title&gt;Bootstrap Case&lt;/title&gt;
    &lt;meta charset="utf-8"&gt;
    &lt;meta name="viewport" content="width=device-width, initial-scale=1"&gt;
    &lt;link rel="stylesheet" href="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css"&gt;
    &lt;script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.2/jquery.min.js"&gt;&lt;/script&gt;
    &lt;script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"&gt;&lt;/script&gt;
  &lt;/head&gt;
  &lt;body&gt;
  
  &lt;nav class="navbar navbar-inverse"&gt;
    &lt;div class="container-fluid"&gt;
      &lt;div class="navbar-header"&gt;
        &lt;button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#myNavbar"&gt;
                               
        &lt;/button&gt;
        &lt;a class="navbar-brand" href="#"&gt;WebSiteName&lt;/a&gt;
      &lt;/div&gt;
      &lt;div class="collapse navbar-collapse" id="myNavbar"&gt;
        &lt;ul class="nav navbar-nav"&gt;
          &lt;li class="active"&gt;&lt;a href="#"&gt;Home&lt;/a&gt;&lt;/li&gt;
          &lt;li class="dropdown"&gt;
            &lt;a class="dropdown-toggle" data-toggle="dropdown" href="#"&gt;Page 1 &lt;span class="caret"&gt;&lt;/span&gt;&lt;/a&gt;
            &lt;ul class="dropdown-menu"&gt;
              &lt;li&gt;&lt;a href="#"&gt;Page 1-1&lt;/a&gt;&lt;/li&gt;
              &lt;li&gt;&lt;a href="#"&gt;Page 1-2&lt;/a&gt;&lt;/li&gt;
              &lt;li&gt;&lt;a href="#"&gt;Page 1-3&lt;/a&gt;&lt;/li&gt;
            &lt;/ul&gt;
          &lt;/li&gt;
          &lt;li&gt;&lt;a href="#"&gt;Page 2&lt;/a&gt;&lt;/li&gt;
          &lt;li&gt;&lt;a href="#"&gt;Page 3&lt;/a&gt;&lt;/li&gt;
        &lt;/ul&gt;
        &lt;ul class="nav navbar-nav navbar-right"&gt;
          &lt;li&gt;&lt;a href="#"&gt;&lt;span class="glyphicon glyphicon-user"&gt;&lt;/span&gt; Sign Up&lt;/a&gt;&lt;/li&gt;
          &lt;li&gt;&lt;a href="#"&gt;&lt;span class="glyphicon glyphicon-log-in"&gt;&lt;/span&gt; Login&lt;/a&gt;&lt;/li&gt;
        &lt;/ul&gt;
      &lt;/div&gt;
    &lt;/div&gt;
  &lt;/nav&gt;
    
  &lt;div class="container"&gt;
    &lt;h3&gt;Collapsible Navbar&lt;/h3&gt;
    &lt;p&gt;In this example, the navigation bar is hidden on small screens and replaced by a button in the top right corner (try to re-size this window).
    &lt;p&gt;Only when the button is clicked, the navigation bar will be displayed.&lt;/p&gt;
  &lt;/div&gt;
  
  &lt;/body&gt;
  &lt;/html&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Still the code is responsive and no visible changes were there.. Is there any use of it? <br>
  Also could you please simply explain why class "sr-only" is used? Thanks in advance.</p>