<span class="menu">
    <tmpl_loop page_loop>
        ...
    </tmpl_loop>
</span>

OR:

<ul class="menu">
    <tmpl_loop page_loop>
        ...
    </tmpl_loop>
</ul>

OR:

<dl class="menu">
    <tmpl_loop page_loop>
        ...
    </tmpl_loop>
</dl>

class="menu" on the containing element of the navigation; this can be a span, ul or dl. Strictly it isn't necessary, however it can be very convenient if a nav has a decriptin, containing a span or ul, for example.