{let list:ListBox = {ListBox "A", "B", "C"}}
{let f:Frame = {Frame "empty"}}
{TabContainer 
    {TabPane 
        label="Row", 
        {HBox spacing=4pt, "A", "B", "C"}
    },
    {TabPane 
        label="Column",
        {VBox spacing=4pt, "A", "B", "C"}
    },
    {TabPane 
        label="List", 
        first-active-control = list, 
        {VBox "Choose One", list}
    },
    {on CurrentPaneChanged at tc:TabContainer do
        {f.add replace?=true, {format "%v", tc.current-pane}}
    }
}
{value f}