traverse( callback ) {

		callback( this );

		const children = this.children;

		for ( let i = 0, l = children.length; i < l; i ++ ) {

			children[ i ].traverse( callback );

		}

	}
Executes the callback on this 3D object and all descendants.

Note: Modifying the scene graph inside the callback is discouraged.

@param {Function} callback - A callback function that allows to process the current 3D object.