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

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

    }
}

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

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