mark pilgrim is toying with the (admitedly evil) idea of intentionally adding a "bug" to safari's handling of CSS for the sake of allowing designers to detect the browser. this functionality can be achieved with minimal harm. a CSS statement such as onlysafari body { display: none; } would be technically valid, and could be interpretted only by safari (despite the lack of any actual <onlysafari> tags in the displayed page). additionally, similar syntax could be handled by all browsers without doing significant damage to the CSS standard.
bugging CSS
Brilliant! It is indeed his duty to do it! Youngpup makes a very good point.