@deftypefun {int} {gnutls_supplemental_register} (const char * @var{name}, gnutls_supplemental_data_format_type_t @var{type}, gnutls_supp_recv_func @var{recv_func}, gnutls_supp_send_func @var{send_func})
@var{name}: the name of the supplemental data to register

@var{type}: the type of the supplemental data format

@var{recv_func}: the function to receive the data

@var{send_func}: the function to send the data

This function will register a new supplemental data type (rfc4680).
The registered data will remain until @code{gnutls_global_deinit()} 
is called. The provided  @code{type} must be an unassigned type in
@code{gnutls_supplemental_data_format_type_t} . If the type is already
registered or handled by GnuTLS internally @code{GNUTLS_E_ALREADY_REGISTERED} 
will be returned.

This function is not thread safe. As supplemental data are not defined under
TLS 1.3, this function will disable TLS 1.3 support globally.

@strong{Returns:} @code{GNUTLS_E_SUCCESS}  on success, otherwise a negative error code.

@strong{Since:} 3.4.0
@end deftypefun