Card's id, shortLink and idShort

Card’s id, shortLink and idShort - what’s the difference between these three?
idShort seems simple - card’s unique id in board’s scope.
Id unique across all boards - simple as well.
What about shortLink tho? It’s unique in scope of board like idShort - why do you need both? Is it just for convenience and creating good looking links or is there some other reason behind it? Is it unique across all boards like id?

I believe that the idShort is only used as the “card number” and is a monotonically increasing number that should be unique within the context of a board. It is only shown in the Trello client under the “Share” card button (at the bottom):

The shortLink is unique across all boards, just like the id, and is used to make a clean, short URL for linking to the card - https://trello.com/c/ZW9pCMWL, for example.