Listing 3

// Registering custom event handlers
if (ctrl is SpecialLabel)
{
  ((SpecialLabel)ctrl).LabelChange += 
    new SpecialLabel.LabelChangeEventHandler(label_changed);    
}
else if (ctrl is SpecialPanel)
{
  ((SpecialPanel)ctrl).PanelChange += 
    new SpecialPanel.PanelChangeEventHandler(panel_changed);    
}