Hi,
I think that my colleague has already answered these questions in a ticket few days ago. I just want to put it here for other visitors.
1) Actually this is purpose of this field. It is intended to be rather suffix to actual class.
2)You can use context selector, i.e. enwrap menu with div with some class, e.g. 'myMenu' and then specify styles for ul within this div using sample code bellow:
.myMenu ul
{
//styles for ul tag within menu
}
Best Regards,
Juraj Ondrus