It can be found in the by-laws:
“First shalt thou take out the Fluther By-laws, then shalt thou count to three, no more, no less. Three shall be the number of thine moderators, and the number of thine moderators shall be three. Four shalt thou not have, neither have’est thou two, excepting that thou then proceedeth to three. Five is right out. Once the number three, being the third number, be reached, then the number of moderators shall be reached and those, who, being naughty in their sight, shall flag it.”
Hope this clears it up.