private static void DemandSecurityPermissionIfCustomPackage(Package package) { // Although ZipPackage is sealed and cannot be subclassed, we shouldn't depend on // the "sealedness" of ZipPackage. Checking the object type is more reliable way // than using "as" or "is" operator. if (package != null && package.GetType() != typeof(ZipPackage)) { SecurityHelper.DemandEnvironmentPermission(); } }