Adding a suffix to a form element
/**
 * Implements hook_form_FORM_ID_alter() for login.
 */
function MYTHEME_form_user_login_form_alter(&amp;$form, &amp;$form_state) {
  $form['register_user']['#prefix'] = &quot;&lt;div class=\&quot;form-footer\&quot;&gt; &lt;span&gt;&quot; . t(&quot;Don't have an account?&quot;) . &quot;&lt;/span&gt;&quot;;
  $form['register_user']['#suffix'] = &quot;&lt;/div&gt;&quot;;
}

This is how I've added a wrapper to a form element using prefix and suffix. Hope it helps.