what makes ThirdPersonController to be grounded?

I checked the scripts attached and non of them move the player to be grounded, if I stick the player half to the ground and half above, when I start the game he just start on top of the ground, what make this magic happen?

I think it just uses rigidbody and capsule collider…

–Belows are deprecated–

ThirdPersonController uses CharacterController.SimpleMove (which automatically touches the ground when you use it in your script) to move the character in every frame even if the player does nothing.