*/
public static UniversalPopup createPopup(Element reference, RelativePopupPositioner positioner,
boolean autoHide, boolean modal,
Widget content, PopupEventListener listener) {
assert popupProvider != null : "PopupProvider not set.";
UniversalPopup popup =
popupProvider.createPopup(reference, positioner, popupChromeProvider == null ? null
: popupChromeProvider.createPopupChrome(), autoHide);
popup.add(content);
popup.addPopupEventListener(listener);
return popup;
}