text: /**
   * Externs declare that access `defaultView` from `document` or
   * `ownerDocument` is of type `(Window|null)` but most of our parameter types
   * assume that it is never null. This is OK in practice as we ever only get
   * null on disconnected documents or old IE.
   * This helper function casts it into just a simple Window return type.
   *
   * @param {?Window} winOrNull
   * @return {!Window}
   */
  export function toWin(winOrNull) {
    return /** @type {!Window} */ (winOrNull);
  }
  