void Form1_Paint(object sender, PaintEventArgs e)
        {
            PopupContainerBarControl barControl = (sender as PopupContainerBarControl);
            Point offsetLocation = new Point(barControl.CloseButton.Location.X + barControl.CloseButton.Width + 3, barControl.CloseButton.Location.Y);

            e.Graphics.DrawString("Custom string", barControl.Font, Brushes.Green, offsetLocation);
        }
        void popupControlContainer1_Popup(object sender, EventArgs e)
        {
            PopupControlContainer    control    = sender as PopupControlContainer;
            PopupContainerBarControl barControl = (control.Parent as PopupContainerBarControl);

            barControl.Paint += Form1_Paint;
        }