It is confusing to show a TemplateSandbox preview when the template being edited is not used on the specified page. It potentially wastes user time if the change being made is subtle. The user should be warned of this situation. Thus:

• When previewing with TemplateSandbox, show an error if the template was not used on the specified page.
• When typing the page title for TemplateSandbox, the autocomplete menu should show a visual indicator of whether the page uses the template