     }
 }
 
+// MARK: Alert
 
 private extension NSAlert {
     static func alertForMinimumSplitAdditionalExtension(minimumAdditionalExtension: CGFloat,

    
    private func allSubPaneViews() -> [PaneView] {
        return self.subviews.filter({ $0.isKindOfClass(PaneView) }) as! [PaneView]
    }
    
    private func indexOfPaneView(paneView: PaneView) -> Int {

    private func select(paneView pane: PaneView?) {
        self.selectedPaneView = pane
        for subPaneView in self.allSubPaneViews() { subPaneView.select(subPaneView == pane) }
        self.window?.makeFirstResponder(pane)
    }
    
    // MARK: - Adding & Removing Subviews
