filter_keys_checked
filter_keys_checked(sk, &filter, &original_keys[f], 1,
filter_keys_checked(sk, &filter, &original_keys[f], 1, "by is_current");
filter_keys_checked(sk, &filter, &original_keys[f], 1, "by is_rnext");
filter_keys_checked(sk, &filter, expected_keys, nmatches,