Minecraft wiki entry for End_Gateway_(block), associated text: Block entity data
Tags common to all block entities[show]
 Age: Age of the portal, in ticks. This is used to determine when the beam is rendered.
 ExactTeleport: 1 or 0 (true/false) - Teleports entities directly to the ExitPortal coordinates instead of near them.
 ExitPortal: Location entities are teleported to when entering the portal.
 X: X coordinate of target location.
 Y: Y coordinate of target location.
 Z: Z coordinate of target location.