     
     // Initializer:
     private func _initializer() {
+        // Set up the height of the tab navigation bar.
+        _setupConstraintOfSelf()
         // Set up container views:
         _setupContainerViews()
         _setupPreviewGesture()

            _constraintBetweenTitleContainerAndItemsContainer = _constraint
        }
        
        self.trailingAnchor.constraint(equalTo: itemsContainerView.trailingAnchor).isActive = true
        self.topAnchor.constraint(equalTo: itemsContainerView.topAnchor).isActive = true
        self.bottomAnchor.constraint(equalTo: itemsContainerView.bottomAnchor).isActive = true
        itemsContainerView.widthAnchor.constraint(lessThanOrEqualTo: self.widthAnchor, multiplier: 0.5, constant: 0.0).isActive = true
    }
    
    private func _setupPreviewGesture() {

    }
    
    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
