/**
* @typedef {object} Phaser.Types.Physics.Impact.WorldWalls
* @since 3.0.0
*
* @property {?Phaser.Physics.Impact.Body} left - The left-side wall of the world bounds.
* @property {?Phaser.Physics.Impact.Body} right - The right-side wall of the world bounds.
* @property {?Phaser.Physics.Impact.Body} top - The top wall of the world bounds.
* @property {?Phaser.Physics.Impact.Body} bottom - The bottom wall of the world bounds.
*/