anchor.diff:    ///
     ///     var event = await ref.once("value");
     ///     print(event.snapshot.val()); //prints 4
  +  ///
  +  /// The returned value from [transactionUpdate] function must be
  +  /// a Dart [Map], [Iterable] or primitive type.
     ///
     /// Set [applyLocally] to [false] to not see intermediate states.
     Future<Transaction> transaction(Func1 transactionUpdate,
  
positive.code:       new OnDisconnect.fromJsObject(jsObject.onDisconnect());
  
    /// Pushes provided [value] to the actual location.
    /// If the [value] is not provided, no data is written to the database
    /// but the [ThenableReference] is still returned and can be used for later
    /// operation.
  
negative.code: 
    /// Sets data at actual database location to provided [value].
    /// Overwrites any existing data at actual location and all child locations.
    ///
    /// The [value] must be a Dart [Map], [Iterable] or primitive type.
    Future set(value) => handleThenable(jsObject.set(jsify(value)));
  
    /// Sets a priority for data at actual database location.
  