Courtesy of KN, the forums now have a new way to hide those game spoilers from accidentally ruining someone else's game experience.
To hide the spoiler, use "["spoiler"]"the text you want to block"["/spoiler"]"
...but lose the quotation marks. End result should look [spoiler]like this[/spoiler]... and you can mouse over the dark area to see what is underneath, if you want.
No button for this yet, but it's a very handy little extra.
Big thanks to KN! :D