On the rules page, it says no killing players unless you're in a designated player killer area and no looting the corpses of dead players. But yet, at least one task I have come across specifically tells you to loot the corpse of the player you've killed in a player killer area. Therefore, in "reality" there's only one rule: no killing players unless you're in a designated player killer area. And since it's the only rule, it's clearly a very important one.