Lack of detail in new mastery...

I'm not surprised, but I am irritated. Expose Weakness: Damaging enemy champion's causes them to take 3% more damaged from your allies.

COOL STORY RIOT. How about details? How long does this last? Does this stack if multiple allies take this mastery and attack the same person? What happens if you proc Expose Weakness, and than die?

Of course I can draw assumptions, I'm sure that this mastery does NOT stack, it probably lasts anywhere from 3 to 5 seconds, and it probably doesn't stop working if you die upon activating it from attacking an enemy. Regardless of assumptions, there are no excuses for the lack of detailed information. This game makes plenty of money, hire people to review new implemented material please.