Xantcha, Sleeper Agent has the ability:
As Xantcha, Sleeper Agent enters the battlefield, an opponent of your choice gains control of it.
The release notes for Commander 2018 describe what happens when a player who controls a permanent owned by another player leaves the game as:
If that player controlled any permanents owned by another player, the effects that gave control of them to the player who left end. If this doesn't give control of them to a different player (perhaps because they entered the battlefield under the control of the player who left), they're exiled.
In the same document, the release notes for Xantcha state:
If the player under whose control Xantcha entered the battlefield leaves the game, the effect changing control of Xantcha ends.
Answers to a previous question lead me to believe that Xantcha's replacement effect causes it to enter the battlefield under an opponent's control and not under my control at all.
Because Xantcha appears to be entering the battlefield under an opponent's control, I thought Xantcha would be exiled when its controller leaves the game.
However, I know this is not what happens because the official Magic: The Gathering Rules Manager has answered a question about it:
What happens to Xantcha when the opponent controlling her dies? Does she get exiled? Returned to my battlefield? Do I get to give her to another opponent? Is all of this in the release notes?
It's all in the release notes, but I'll tell you! You end up with Xantcha. Will you keep her as your poisonous friend, or kill her so you can pop a new Xantcha out of the vat? #WotCStaff
So I know what is supposed to happen - Xantcha's owner is supposed to gain control of it when its current controller leaves the game. What I want to know is the full explanation within the rules of what causes this result to happen.