Update readme.

Readme.md

@@ -116,15 +116,16 @@ ThreadFiber does not support pause. It is specifically intended for performance-
  * _[ThreadPoolAdaptorFromQueueForThread](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorks/Core/ThreadPoolAdaptorFromQueueForThread.cs)_ - A thread pool that uses a single existing thread as a worker thread.  Convenient to combine with the main thread.
 
 ## Channels ##
-A channel is a messaging mechanism that abstracts the communication destination.  Channel functionality has not changed much from the original Retlang design concept. The following explanation is quoted from Retlang.
+A channel is a messaging mechanism that abstracts the communication destination.  Used for 1:1 unicasting, 1:N broadcasting and N:1 message aggregation.
+
+ * _[Channel](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorks/Channels/Channel.cs)_ - Forward published messages to all subscribers.  One-way.  [Example](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorksTests/ChannelTests.cs#L18).
+ * _[AcknowledgementChannel](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorks/Channels/AcknowledgementChannel.cs)_ - Forward and acknowledge the published message to all or some of the subscribers.  [Example](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorksTests/AcknowledgementChannelTests.cs#L17).
+
+### Design concept ###
+Channel functionality has not changed much from the original Retlang design concept. The following explanation is quoted from Retlang.
 
 > Message based concurrency in .NET
 > \[...\]
 > The library is intended for use in [message based concurrency](http://en.wikipedia.org/wiki/Message_passing) similar to [event based actors in Scala](http://lampwww.epfl.ch/~phaller/doc/haller07actorsunify.pdf).  The library does not provide remote messaging capabilities. It is designed specifically for high performance in-memory messaging.
 
 (Quote from [Retlang page](https://code.google.com/archive/p/retlang/). Broken links were replaced.)
-
-### Channel classes ###
-
- * _[Channel](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorks/Channels/Channel.cs)_ - Forward published messages to all subscribers.  One-way.  Used for 1:1 unicasting, 1:N broadcasting and N:1 message aggregation.  [Example](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorksTests/Examples/BasicExamples.cs#L20).
- * _[SnapshotChannel](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorks/Channels/SnapshotChannel.cs)_ - Subscribers are also notified when they start subscribing, and separately thereafter.  One-way. Used for replication with incremental update notifications.  Only one responder can be handled within a single channel.  [Example](https://github.com/tosh-coding/AsyncFiberWorks/blob/main/src/AsyncFiberWorksTests/Examples/BasicExamples.cs#L189).