Improve documentation for Isolate.kill.

sdk/lib/isolate/isolate.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Concurrent programming using _isolates_:
  * independent workers that are similar to threads
  * but don't share memory,
  * communicating only via messages.
  *
@@ skipping 421 matching lines @@
    * then resume the isolate.
    */
   external void setErrorsFatal(bool errorsAreFatal);
 
   /**
    * Requests the isolate to shut down.
    *
    * The isolate is requested to terminate itself.
    * The [priority] argument specifies when this must happen.
    *
-   * The [priority] must be one of [IMMEDIATE] or [BEFORE_NEXT_EVENT].
+   * The [priority], when provided, must be one of [IMMEDIATE] or
+   * [BEFORE_NEXT_EVENT] (the default).
    * The shutdown is performed at different times depending on the priority:
    *
    * * `IMMEDIATE`: The isolate shuts down as soon as possible.
    *     Control messages are handled in order, so all previously sent control
    *     events from this isolate will all have been processed.
    *     The shutdown should happen no later than if sent with
    *     `BEFORE_NEXT_EVENT`.
    *     It may happen earlier if the system has a way to shut down cleanly
    *     at an earlier time, even during the execution of another event.
    * * `BEFORE_NEXT_EVENT`: The shutdown is scheduled for the next time
@@ skipping 251 matching lines @@
  * as the original error, but has no other features of the original error.
  */
 class RemoteError implements Error {
   final String _description;
   final StackTrace stackTrace;
   RemoteError(String description, String stackDescription)
       : _description = description,
         stackTrace = new StackTrace.fromString(stackDescription);
   String toString() => _description;
 }