WidgetDim (WidgetName + "__auto__TabPane__", TopEdge) + 4 +
PropertyDim (WidgetName + "__auto_TabPane__Buttons", "EnableTop") *
    (WidgetDim (WidgetName + "__auto_TabPane__", Height) -
     (ImageDim ("WindowsLook", "TabButtonScrollLeftNormal", Width) + 6))