Well holy crappolie. Andy Smith posted a real nugget of info related to CSS classes that I had no idea about. Maybe everyone else knows about this - but it sure was news to me. You can put multiple CSS class names inside the same class attribute separated by a space. Who knew?! Take a look.
border: 1px solid black;
<span class="foo bar"></span>
I suppose that says a lot for actually taking the time to read the spec.