IntersectionObserver constructor: support document root
@@ -107,7 +107,7 @@ var IntersectionObserverCallback;
* threshold: (!Array<number>|number|undefined),
* delay: (number|undefined),
* trackVisibility: (boolean|undefined),
- * root: (?Element|undefined),
+ * root: (?Document|?Element|undefined),
* rootMargin: (string|undefined)
* }}
*/
