This specification defines a TLS handshake message for exchange of supplemental application data. TLS hello message extensions are used to determine which supplemental data types are supported by both the TLS client and the TLS server. Then@ the supplemental data handshake message is used to exchange the data. Other documents will define the syntax of these extensions and the syntax of the associated supplemental data types.
RFC 4680-2006 history
2006RFC 4680-2006 TLS Handshake Message for Supplemental Data