The function is static, meaning that you should call it directly on the class, rather than on the instance:
I see the documentation doesn't say that, I'll fix it.
function OnSomeHook(a_Player) a_Player:XpForLevel(60); -- WRONG cPlayer:XpForLevel(60); -- CorrectIt's the same as cPluginManager:AddHook() and all the cFile functions.
I see the documentation doesn't say that, I'll fix it.