         }
     }
 }
+
+private extension MasterViewController {
+    
+    /// The sections displayed in the collection view.
+    private enum CollectionSection: Hashable {
+        case counties
+    }
+}

        super.viewDidLoad()
        navigationItem.searchController = searchController
        definesPresentationContext = true
    }
    
    override func willTransition(to newCollection: UITraitCollection, with coordinator: UIViewControllerTransitionCoordinator) {

// MARK: UICollectionViewDelegate
extension MasterViewController: UICollectionViewDelegate {
    func collectionView(_ collectionView: UICollectionView, didSelectItemAt indexPath: IndexPath) {
        showCounty(dataSource.itemIdentifier(for: indexPath)!, animated: true)
        collectionView.deselectItem(at: indexPath, animated: false)
    }
}
