listenToXRControllerEvents( controller ) {

		this.controllers.push( controller );
		controller.addEventListener( 'move', this._onXRControllerEvent );
		controller.addEventListener( 'select', this._onXRControllerEvent );
		controller.addEventListener( 'selectstart', this._onXRControllerEvent );
		controller.addEventListener( 'selectend', this._onXRControllerEvent );

	}
Calling this method makes sure the interactive group listens to events of
the given XR controller.

@param {Group} controller - The XR controller.