function onSessionEvent( event ) {

			const controllerIndex = controllerInputSources.indexOf( event.inputSource );

			if ( controllerIndex === -1 ) {

				return;

			}

			const controller = controllers[ controllerIndex ];

			if ( controller !== undefined ) {

				controller.update( event.inputSource, event.frame, customReferenceSpace || referenceSpace );
				controller.dispatchEvent( { type: event.type, data: event.inputSource } );

			}

		}
Returns a group representing the `hand` space of the XR controller.
Use this space for visualizing 3D objects that support the user in pointing
tasks like UI interaction.

@param {number} index - The index of the controller.
@return {Group} A group representing the `hand` space.