     
     internal func _toggleShowingOfNavigationBackItem(shows: Bool, duration: TimeInterval = 0.5, animated: Bool) {
         if let _horizontal = _horizontalConstraintOfBackItem {
-            removeConstraint(_horizontal)
+            _containerView.removeConstraint(_horizontal)
         }
         var _horizontal: NSLayoutConstraint
         if shows {
-            _horizontal = _navigationBackItem._view.leadingAnchor.constraint(equalTo: leadingAnchor)
-        } else {
-            _horizontal = _navigationBackItem._view.trailingAnchor.constraint(equalTo: leadingAnchor)
+            _horizontal = _navigationBackItem._view.leadingAnchor.constraint(equalTo: _containerView.leadingAnchor)
+        } else {
+            _horizontal = _navigationBackItem._view.trailingAnchor.constraint(equalTo: _containerView.leadingAnchor)
         }
         _horizontal.isActive = true
         _horizontalConstraintOfBackItem = _horizontal

        layoutIfNeeded()
    }
    
    private func _setupContainerViews() {
        _navigationBackItem._view.isHidden = true
        addSubview(_navigationBackItem._view)
        _navigationBackItem._view.centerYAnchor.constraint(equalTo: centerYAnchor).isActive = true
        let _horizontal = _navigationBackItem._view.trailingAnchor.constraint(equalTo: leadingAnchor)
        _horizontal.isActive = true
        _horizontalConstraintOfBackItem = _horizontal
        _setupTitleItemsContainerView(_titleItemsContainerView)

    }
    
    private func _setupTitleItemsContainerView(_ itemsContainerView: UIView) {
        _containerView.addSubview(itemsContainerView)
        
        _navigationBackItem._view.trailingAnchor.constraint(equalTo: itemsContainerView.leadingAnchor).isActive = true
        _containerView.topAnchor.constraint(equalTo: itemsContainerView.topAnchor).isActive = true
        _containerView.bottomAnchor.constraint(equalTo: itemsContainerView.bottomAnchor).isActive = true
    }
    
    private func _setupNavigationItemsContainerView(_ itemsContainerView: UIView, transition: Bool = false) {
        _containerView.addSubview(itemsContainerView)
        
        let _constraint = _titleItemsContainerView.trailingAnchor.constraint(equalTo: itemsContainerView.leadingAnchor, constant: -DefaultTabNavigationItemEdgeMargin)
        _constraint.isActive = true
