Main Menu Display Description as span Tag
Looks like your friend is: $element['#original_link']['depth'];

You would adjust your conditional to be something like:

 // Not sure if top level depth is 0 or 1 for this so experiment with that a bit.
 if ($element['#original_link']['menu_name'] == "main-menu" &amp;&amp; 
     isset($element['#localized_options']['attributes']['title']) &amp;&amp;
     $element['#original_link']['depth'] == 0
 ){
    $element['#title'] .= '&lt;span class="description"&gt;' . $element['#localized_options']['attributes']['title'] . '&lt;/span&gt;';
 }


Check out this comment from the drupal documentation.