update

docs/consuming-any-topic.adoc

@@ -3,24 +3,14 @@ Consuming Arbitrary Topic
 :base_version: 9.0.0
 :modules: common,protocol,processor
 
-This document covers an advanced usage of Decaton processor when you process topics containing records not produced by DecatonClient.
+This document guides you how to consume and process topics containing records not produced by DecatonClient using Decaton processors.
 
-[NOTE]
-====
-* From Decaton 9.0.0, DecatonClient no longer wraps tasks with DecatonTaskRequest protobuf message.
-** The wrapper was a heritage from the time when Kafka didn't support record headers to store task metadata.
-** Now task metadata is stored in record headers instead, so there are no differences in wire format between tasks produced by DecatonClient and by other clients.
-* Hence, you can just use link:../processor/src/main/java/com/linecorp/decaton/processor/runtime/ProcessorsBuilder.java[ProcessorsBuilder#consuming(String topic, Deserializer<T> deserializer)] to process arbitrary topics in most cases.
-** So the expected use cases of this guide are:
-*** You need to apply custom task metadata extraction logic. (e.g. Set `scheduledTimeMillis` for delayed processing)
-*** You need to access additional information (e.g. record headers) for deserialization
-====
-
-By default, Decaton assumes messages are produced by DecatonClient where task metadata is stored as link:../protocol/src/main/proto/decaton.proto[TaskMetadataProto] in record headers.
+By default, Decaton assumes messages are produced `DecatonClient`, where task metadata are stored as link:../protocol/src/main/proto/decaton.proto[TaskMetadataProto] in record headers.
+But Decaton has the capability to consume arbitrary topics other than topics produced by `DecatonClient`.
 
-When you consume a topic not produced by DecatonClient, you can apply custom task metadata extraction logic.
+This means you can use Decaton as a drop-in replacement for a vanilla KafkaConsumer to leverage powerful features like deferred completion, delayed processing and so on.
 
-Through this guide, we assume the topic is JSON-serialized and use link:https://github.com/FasterXML/jackson-databind[jackson-databind] for deserialization, but it's trivial to apply to arbitrary formats other than JSON.
+Through this guide, we assume the topic is JSON-serialized and use link:https://github.com/FasterXML/jackson-databind[jackson-databind] for deserialization, but it's trivial to consume arbitrary formats other than JSON.
 
 == TaskExtractor