Leading "header" in collectionView

I implemented this code (XCode 11.2:

h ttps://medium.com/flawless-app-stories/all-what-you-need-to-know-about-uicollectionviewcompositionallayout-f3b2f590bdbe

I was specially interested in the supplementaryViews for compositionalLayout.

And discovered the leading and trailing headers:

   private func createLayout() -> UICollectionViewLayout {
        let itemSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),
                                             heightDimension: .fractionalHeight(1.0))
        let item = NSCollectionLayoutItem(layoutSize: itemSize)
        item.contentInsets = NSDirectionalEdgeInsets(top: 8, leading: 8, bottom: 8, trailing: 8)
        let groupSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.9),
                                              heightDimension: .absolute(50))
        let group = NSCollectionLayoutGroup.horizontal(layoutSize: groupSize,
                                                         subitems: [item])
        group.edgeSpacing = NSCollectionLayoutEdgeSpacing(leading: .flexible(0),
                                                          top: nil,
                                                          trailing: nil,
                                                          bottom: nil)


        let footerHeaderSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(1.0),
                                                      heightDimension: .absolute(50.0))
        let leftSize = NSCollectionLayoutSize(widthDimension: .fractionalWidth(0.1),
                                              heightDimension: .absolute(150.0))
        let header = NSCollectionLayoutBoundarySupplementaryItem(layoutSize: footerHeaderSize,
                                                                 elementKind: HeaderFooterViewController.headerKind,
                                                                 alignment: .top)
        let footer = NSCollectionLayoutBoundarySupplementaryItem(layoutSize: footerHeaderSize,
                                                                 elementKind: HeaderFooterViewController.footerKind,
                                                                 alignment: .bottom)
        let left = NSCollectionLayoutBoundarySupplementaryItem(layoutSize: leftSize,
                                                               elementKind: HeaderFooterViewController.leadingKind,
                                                               alignment: .leading)
        let section = NSCollectionLayoutSection(group: group)
        section.boundarySupplementaryItems = [header, footer, left]


        let config = UICollectionViewCompositionalLayoutConfiguration()
        config.interSectionSpacing = 16
        let layout = UICollectionViewCompositionalLayout(section: section, configuration: config)


        return layout
    }

There is one point though.

For headers, I changed elementKind: HeaderFooterViewController.headerKind to elementKind: UICollectionView.elementKindSectionHeader ; it works pefectly.

For left, I need to change elementKind: HeaderFooterViewController.leadingKind in a similar way, but to which elementKind ? elementKindLeading does not compiles…

Does CollectionView support these leading and trailing supplementary items ? They are not referenced in doc:

Class. UICollectionView

class let elementKindSectionFooter: String

class let elementKindSectionHeader: String