     
     // MARK: - Editing
 
-    func forceEndEditing() {
+    private func forceEndEditing() {
         self.window?.makeFirstResponder(self)
     }
 

    
    // MARK: - Selection
    
    func selectTab(sender: AnyObject?) {
        guard let button = sender as? TabButton else {
            return
        }

        }
    }
    
    private func visibilityCondition(button: NSButton, forLeft: Bool) -> Bool {
        let visibleRect = self.tabsView.visibleRect
        if forLeft == true {
            return NSMinX(button.frame) < NSMinX(visibleRect)
