     // MARK: Calculation.
     
     fileprivate func _updateWidthConstantOfContentAlignmentView(`in` titleItems: [TabNavigationTitleItem]? = nil, possibleActions actionItems: [TabNavigationTitleActionItem]? = nil, transition: Bool = false) {
-        let items   = titleItems  ?? _navigationTitleItems
+        let items = titleItems  ?? _navigationTitleItems
+        /*
+        guard !items.isEmpty else {
+            _widthOfTitleItemContentAlignmentView(transition)?.constant = 0.0; return
+        } */
+        
+        // _widthOfTitleItemContentAlignmentView(transition)?.constant = -_horizontalSpace(for: items.last!)
         let actions = actionItems ?? _navigationTitleActionItems
         
-        guard !items.isEmpty && !actions.isEmpty else {
+        guard !items.isEmpty || !actions.isEmpty else {
             _widthOfTitleItemContentAlignmentView(transition)?.constant = 0.0; return
         }
         

    /// Calculate the bounding size for the TabNavigationTitleItem by bounding the underlying title of the button
    /// the button's bounds.
    func _boundingSize(`for` item: TabNavigationTitleItem, selected: Bool = false) -> CGSize {
        var titleString = item.underlyingButton.currentTitle
        if let _ = item.selectedRange {
            titleString = item.underlyingButton.currentAttributedTitle?.string
        }
        
        let size = (titleString as NSString?)?.boundingRect(with: CGSize(width: CGFloat.greatestFiniteMagnitude, height: self.bounds.height), options: [.usesLineFragmentOrigin, .usesFontLeading], attributes: [NSFontAttributeName:item.titleFont(whenSelected: selected)], context: nil).size ?? .zero
        
        return size
    }

    @objc
    private func _handleDidSelectTitleItem(_ sender: _TabNavigationTitleItemButton) {
        guard let _titleItem = sender._titleItem else { return }
        
        if let index = _navigationTitleItems.index(of: _titleItem), index != _selectedTitleItemIndex {
            // setSelectedTitle(at: index, animated: true)
            _setSelectedTitle(at: index, in: _navigationTitleItems, animated: true)
            // Cancel the scheduled scrolling animation if exists.
            NSObject.cancelPreviousPerformRequests(withTarget: self,
                                                   selector  : #selector(_scrollToSelectedTitleItemWithAnimation),
                                                   object    : nil)
            // Set up the animated transition delegate:
            _delegatesQueue.remove(_interactiveTransition)
            _delegatesQueue.add(_animatedTransition)
            // Set to the selected offset.
            let offsetx = _horizontalOffset(upto: _selectedTitleItemIndex, in: _navigationTitleItems)
            _titleItemsScrollView.setContentOffset(CGPoint(x: offsetx, y: 0.0), animated: true)
        }
    }
    
