... to show popup windows that are smaller than a certain size and, depending on settings, may show pop-up windows as separate tabs in the current window. • When calling PopupWindow(), you must ... hard-coding details that the control consumer may want to customize. Instead, you need to use template binding expressions. In this example, you set several properties using template-binding expressions: ... BorderBrush="{TemplateBinding BorderBrush}" BorderThickness="{TemplateBinding BorderThickness}" CornerRadius="{TemplateBinding CornerRadius}" Background="{TemplateBinding Background}">...