KnpMenuBundle and Twitter Bootstrap styles

Params:
Symfony2.1 RC2 and appropriate KnpMenuBundle
Twitter Bootstrap 2.1

Problem:
Need to customize Menu by Bootstrap css classes.
For example, I need to add attribute class="nav" to <ul> element of generated menu.

Solution:
Using methods setAttribute(), setChildrenAttributes(), ...
Example:
$menu = $factory->createItem('root');
$menu->setChildrenAttributes(array('class' => 'nav'));
$menu->addChild('Home', array('route' => 'bst_app_homepage'));
...
The output will be:
<ul class="nav">
   <li>...</li>
</ul>