apache kafka – Is there any specification to describe the functionality of KafkaAvroSerializer / KafkaAvroDeserializer or the confluent platform registry?

I am wondering whether the confluent schema-registry paradigm (which to my understanding is paired with KafkaAvroSerializer/KafkaAvroDeserializer implementation) changes over time. If it does, is it based on some publicly available specification?

I consider that I should somehow be able to know what types of requests (GET/POST/PUT e.t.c.) the KafkaAvroSerializer and KafkaAvroDeserializer are supposed to perform to the confluent-schema registry and how it is decided whether a schema will be added to the registry or not.

Also in the second diagram below I see that kafka communicates with the schema-registry for validating
the schema. But every answer I have seen till now is that kafka does not know anything about schemas.

Is this a recent change? Is depicted to a change-log intended for maintainers of project using confluent registry?

From page: docs.confluent.io/platform/6.2/schema-registry/index.html

From page: docs.confluent.io/platform/7.5/schema-registry/index.html