         super.viewDidDisappear(animated)
         unregisterForPreviewing()
     }
-    
-    // MARK - UICollectionViewDataSource
+}
+
+// MARK: - UICollectionViewDataSource
+extension NewsViewController {
     
     override func numberOfSections(in collectionView: UICollectionView) -> Int {
         return stories.count

    }
}

extension NewsViewController: NewsCollectionViewCellDelegate {
    func newsCollectionViewCell(_ newsCollectionViewCell: NewsCollectionViewCell, didSelectNewsArticleWithURL articleURL: URL) {
        wmf_pushArticle(with: articleURL, dataStore: dataStore, animated: true)
    }
}

extension NewsViewController { // UIViewControllerPreviewingDelegate
    override func previewingContext(_ previewingContext: UIViewControllerPreviewing, viewControllerForLocation location: CGPoint) -> UIViewController? {
        guard let collectionView = collectionView,
            let indexPath = collectionView.indexPathForItem(at: location),

    }
}

// MARK: - WMFColumnarCollectionViewLayoutDelegate
extension NewsViewController {
    override func collectionView(_ collectionView: UICollectionView, estimatedHeightForHeaderInSection section: Int, forColumnWidth columnWidth: CGFloat) -> CGFloat {
        return headerTitle(for: section) == nil ? 0 : 50
    }
