anchor.diff:  /// when sent.
   abstract class SendPort implements Capability {
     /// Sends an asynchronous [message] through this send port, to its
  -  /// corresponding `ReceivePort`.
  -  ///
  -  /// The content of [message] can be:
  +  /// corresponding [ReceivePort].
  +  ///
  +  /// The transitive object graph of [message] can contain the following
  +  /// objects:
     ///   - [Null]
     ///   - [bool]
     ///   - [int]
  
positive.code:   ///   - [SendPort]
    ///   - [Capability]
    ///
    /// In the special circumstances when two isolates share the same code and are
    /// running in the same process (e.g. isolates created via [Isolate.spawn]),
    /// it is also possible to send object instances (which would be copied in the
    /// process).
    ///
    /// The send happens immediately and doesn't block.  The corresponding receive
    /// port can receive the message as soon as its isolate's event loop is ready
    /// to deliver it, independently of what the sending isolate is doing.
    void send(Object? message);
  
    /// Tests whether [other] is a [SendPort] pointing to the same
  
negative.code:   /// code will run in the isolate.)
    ///
    /// If [finalMessagePort] is provided, and the [message] can be sent through
    /// it (see [SendPort.send] for more details), then the message is sent
    /// through that port as the final operation of the current isolate. The
    /// isolate terminates immediately after that [SendPort.send] call returns.
    ///
    /// If the port is a native port -- one provided by [ReceivePort.sendPort] or
    /// [RawReceivePort.sendPort] -- the system may be able to send this final
  