                                                                                         -> (CGFloat, CGFloat) {
             // get attributes for first and last items in section
             guard let collectionView = collectionView  else { return (0, 0) }
-
             let section = sectionHeadersLayoutAttributes.indexPath.section
             
             // Trying to use layoutAttributesForItemAtIndexPath for empty section would

    }
    
    // MARK: - 🕶Private Helpers
    private let _zIndexForSectionHeader = 1024
    
    // iOS9 supports sticky headers natively, so see if it should be used instead
    private var _shouldDoCustomLayout: Bool {
        return !sectionHeadersPinToVisibleBounds
    }

    /// Given a rect, calculates indexes of confined section headers
    private func sectionsHeadersIDxs(forRect rect: CGRect) -> Set<Int>? {

        // insets of the first section
        var theSectionInset = sectionInset
        if let delegate = collectionView.delegate as? UICollectionViewDelegateFlowLayout
                                                            where theSectionInset == UIEdgeInsetsZero {
            theSectionInset = delegate.collectionView!(collectionView,
                                                       layout: self,
                                                       insetForSectionAtIndex: 0)
        }
        return (firstSectionHeight, theSectionInset)
    }
}


