Displays a tool tip for the given help event.
        
        :param      event | <QHelpEvent>

def helpEvent( self, event ):
        """
        Displays a tool tip for the given help event.
        
        :param      event | <QHelpEvent>
        """
        item  = self.itemAt(event.scenePos())
        if ( item and item and item.toolTip() ):
            parent = self.parent()
            rect   = item.path().boundingRect()
            point  = event.scenePos()
            point.setY(item.pos().y() + rect.bottom())
            
            point  = parent.mapFromScene(point)
            point  = parent.mapToGlobal(point)
            
            XPopupWidget.showToolTip(item.toolTip(),
                                     point = point,
                                     parent = parent)
            event.accept()
        else:
            super(XCalendarScene, self).helpEvent(event)