Minecraft wiki entry for experience, associated text: Specifies the amount of experience points or levels to be added to the player. Negative values remove experience instead of adding them.
Must be a 32-bit integer number.
If the amount is expressed in points, it must be between 0 and 2,147,483,647 (inclusive, without the commas).
If the amount is expressed in levels, it must be between -2,147,483,648 and 2,147,483,647 (inclusive, without the commas).