The Exp Flask is an unobtainable tool used for storing vanilla Minecraft experience.
The Exp Flask cannot be obtained in survival mode.
The Exp Flask is used for storing vanilla Minecraft experience. The player can see how much Experience they have collected on the Exp Flask's tooltip.
When the Exp Flask is in the player's hotbar, any vanilla Minecraft experience from an XP Orb that the player collects will be added to the Exp Flask and not to the player's Experience bar.
The priority of Exp Flask is higher than Mending, so Mending will lose its effect completely.
The player can retrieve the experience stored in the Exp Flask by holding down the use button while holding the Exp Flask, similar to eating food. As the player holds the use button down, experience will be gradually removed from the Exp Flask and added to the player's Experience bar directly.
The priority of this usage is also greater than Mending.