Drop rate settings explanation

Can someone explain how the worldserver.conf drop rate settings work?

Rate.Drop.Item.Legendary = 1

If I set that to 2 is that a x2 chance on the default rate?

Why does setting it to 0 for Poor and Normal still result in drops?

What is

Rate.Drop.Item.Referenced = 1

And

Rate.Drop.Item.ReferencedAmount = 1