code: function VirtualizeContentsView_updateAriaForAnnouncement(item, count) {
                      if (item === this._listView.header || item === this._listView.footer) {
                          return;
                      }
  
                      var index = -1;
                      var type = _UI.ObjectType.item;
                      if (_ElementUtilities.hasClass(item, _Constants._headerClass)) {
                          index = this._listView._groups.index(item);
                          type = _UI.ObjectType.groupHeader;
                          _ElementUtilities._setAttribute(item, "role", this._listView._headerRole);
                          _ElementUtilities._setAttribute(item, "tabindex", this._listView._tabIndex);
                      } else {
                          index = this.items.index(item);
                          _ElementUtilities._setAttribute(item, "aria-setsize", count);
                          _ElementUtilities._setAttribute(item, "aria-posinset", index + 1);
                          _ElementUtilities._setAttribute(item, "role", this._listView._itemRole);
                          _ElementUtilities._setAttribute(item, "tabindex", this._listView._tabIndex);
                      }
  
                      if (type === _UI.ObjectType.groupHeader) {
                          this._listView._fireAccessibilityAnnotationCompleteEvent(-1, -1, index, index);
                      } else {
                          this._listView._fireAccessibilityAnnotationCompleteEvent(index, index, -1, -1);
                      }
                  }
docs: Update the ARIA attributes on item that are needed so that Narrator can announce it. item must be in the items container.