How are all diminishing returns calculated in League of Legends?
I know that Cooldown Reduction is capped at 40%, and Attack Speed at 2.5 (i.e. +150% to cap?). What are the various caps for all the equipment properties (life steal, armor, +%damage etc.), and which of these are limited to just a single source? (e.g. Rabadon's Deathcap gives +%AP, I'm not aware of any other item with this property).