         }
     }
     
-    fileprivate func _toggleShowingOfNavigationBackItem(shows: Bool, animated: Bool) {
+    internal func _toggleShowingOfNavigationBackItem(shows: Bool, duration: TimeInterval = 0.5, animated: Bool) {
         if let _horizontal = _horizontalConstraintOfBackItem {
             removeConstraint(_horizontal)
         }

        return Selector(_selector)
    }
    
    fileprivate var _view: _TabNavigationItemView = _TabNavigationItemView()
    
    public init(title: String?) {


extension TabNavigationBar {
    public typealias TabNavigationItemViews = (itemsContainerView: UIView, itemsScrollView: UIScrollView, itemsView: UIView)
    public typealias TabNavigationItemAnimationViews = (fromItemViews: TabNavigationItemViews, toItemViews: TabNavigationItemViews)
    public typealias TabNavigationTitleItemViews = (itemsScrollView: UIScrollView, itemsView: UIView, alignmentContentView: UIView)
    public typealias TabNavigationTitleItemAnimationViews = (containerView: UIView, fromItemViews: TabNavigationTitleItemViews, toItemViews: TabNavigationTitleItemViews)
    public typealias TabNavigationTransitionViews = (backItem: TabNavigationItem, titleViews: TabNavigationTitleItemAnimationViews, itemViews: TabNavigationItemAnimationViews)
}

public class TabNavigationBar: UIView, UIBarPositioning {
