In Ff3.0.x, Ff3.5.x, IE6 and IE7, this will be interpreted as a single opening tag, therefore everything coming later will be inside that class.
I haven't tested it with browsers others than those listed above, because it does not help me out if Opera, Chrome, Safari or whatever correctly supports it. (Though it would be nice to see that they do.)
Has anybody a faint idea what is the reasoning behind this strange and shocking behaviour?