You can specify how long you want the server to keep cached files with URLs matching a given template. The server deletes or revalidates cached files whose URLs match the template after they have been cached for the specified time, regardless of their expiration dates.
Because two options exist for the server's behavior with respect to these cached files, this form allows you to create two separate lists. Files in the first list will be deleted after the specified time has passed. Files in the second list will be revalidated after the specified time has passed.