     private var documentObserver: NSObjectProtocol?
     private var syntaxStyleObserver: NSObjectProtocol?
     private var selectionObserver: NSObjectProtocol?
+    private var fontSizeObserver: UserDefaultsObservation?
     private var isOwnSelectionChange = false
-    
-    private var fontSizeObserver: UserDefaultsObservation?
     
     @IBOutlet private weak var outlineView: NSOutlineView?
     

            guard let self = self else { return assertionFailure() }
            
            self.observeSyntaxStyle()
            self.outlineView?.reloadData()
            
            self.invalidateCurrentLocation()
        }
    }

    override var representedObject: Any? {
        
        didSet {
            assert(representedObject == nil || representedObject is Document,
                   "representedObject of \(self.className) must be an instance of \(Document.className())")
            
            self.observeDocument()
            self.observeSyntaxStyle()
            
