title: Defining a `required` field in Bootstrap
body: <p>How do I define text field as required (with red border) in Twitter Bootstrap 3?</p>
  
  <p><code>required="required"</code> doesn't work...</p>
  
  <pre class="lang-html prettyprint-override"><code>&lt;form role="form"&gt;
    &lt;div class="form-group"&gt;
      &lt;label for="exampleInputEmail1"&gt;Email address&lt;/label&gt;
      &lt;input type="email" class="form-control" id="exampleInputEmail1" placeholder="Enter email"&gt;
    &lt;/div&gt;
    &lt;div class="form-group"&gt;
      &lt;label for="exampleInputPassword1"&gt;Password&lt;/label&gt;
      &lt;input type="password" class="form-control" id="exampleInputPassword1" placeholder="Password"&gt;
    &lt;/div&gt;
    &lt;div class="form-group"&gt;
      &lt;label for="exampleInputFile"&gt;File input&lt;/label&gt;
      &lt;input type="file" id="exampleInputFile"&gt;
      &lt;p class="help-block"&gt;Example block-level help text here.&lt;/p&gt;
    &lt;/div&gt;
    &lt;div class="checkbox"&gt;
      &lt;label&gt;
        &lt;input type="checkbox"&gt; Check me out
      &lt;/label&gt;
    &lt;/div&gt;
    &lt;button type="submit" class="btn btn-default"&gt;Submit&lt;/button&gt;
  &lt;/form&gt;
  </code></pre>