Read Thread: Spoiler tags?
Actually.... it is on the markup comparisons page. I was a little lazy trying to work it into the Wiki and HTML markup pages, though, neither of which is as complete as the markup comparisons page. (You also won't find the wassa tag except on the comparisons page.)
I'll get around to fixing the other pages... eventually. =)
Hmm, I was unaware of that page. Good to know. Thanks!