When people metacommunicate, they are sending messages about

When people metacommunicate, they are sending messages about messages themselves.

Metacommunication is the layer of signals that tells the receiver how to read the primary message, its tone, seriousness or intent.

Saying I am only joking, or shifting one's voice, comments on the message being exchanged rather than on the parties or the medium.

It is not about the senders, since it does not describe or refer to the source of the communication.

It is not about the receivers, because it does not carry information regarding those who take in the message.

It is not about the channels either, as it concerns how to interpret the content, not the medium carrying it.