Extended version of listener inteface. Not only reactos on user events but
also provides a function for reacting, when the popup is closed due to
parent-child relationships of popups.
Example: on top of a modal popup, a modeless popup is opened (as dialog, not
as frame). In this case the modeless popup is closed when the parent popup is closed
as well. The closing of the modeless popup is reported to the server side
via
BasePopup.IPopupListener2.reactOnPopupClosedByClient() in this case.
As reaction you only can "save the work" of the popup - you cannot avoid the closing.
For documentation of the user closing the popup see
ModelessPopup.IModelessPopupListener.