[TLS] What is the KDF of the combined classical and PQC keys i n TLS 1.3 PQC hybrid?

I apologize in advance if this is the wrong forum for asking a technical question about the emerging standard.

Regarding RFC 9954 : https://datatracker.ietf.org/doc/rfc9954/

As I understand the process I'm interested in:
The client sends X25519 ephemeral public key and MLKEM768 encapsulation key to the server.
The server sends back its X25519 ephemeral public key and MLKEM768 ciphertext to the client.
They both, separately, generate both a shared classical key and a shared PQC key.
These keys are concatenated together to create a single shared key.

In the RFC, it states this:

concatenated_shared_secret = MyECDH.shared_secret
                                || MyPQKEM.shared_secret

Is that concatenation simply appending one string to the other?

Roger

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