diff -crB gnutls.orig/doc/cha-internals.texi gnutls/doc/cha-internals.texi
*** gnutls.orig/doc/cha-internals.texi	2012-02-24 17:04:27.000000000 +0100
--- gnutls/doc/cha-internals.texi	2012-02-24 17:06:50.000000000 +0100
***************
*** 321,326 ****
--- 321,421 ----
  forget to add @code{Since:} tags to indicate the GnuTLS version the
  API was introduced in.
  
+ @subheading Adding a new Supplemental Data Handshake Message
+ 
+ TLS handshake extensions allow to send so called supplemental data
+ handshake messages. This short section explains how to implement a
+ supplemental data handshake message for a given TLS extension.
+ 
+ First of all, modify your extension @code{foobar} in the way, the that
+ flags
+ @code{session->security_parameters.do_send_supplemental}
+ and
+ @code{session->security_parameters.do_recv_supplemental}
+ are set:
+ 
+ @example
+ int
+ _gnutls_foobar_recv_params (gnutls_session_t session, const opaque * data,
+                                  size_t _data_size)
+ @{
+    ...
+    session->security_parameters.do_recv_supplemental=1;
+    ...
+ @}
+ 
+ int
+ _gnutls_foobar_send_params (gnutls_session_t session, gnutls_buffer_st *extdata)
+ @{
+    ...
+    session->security_parameters.do_send_supplemental=1;
+    ...
+ @}
+ @end example
+ 
+ Furthermore add the functions @funcintref{_foobar_supp_recv_params}
+ and @funcintref{_foobar_supp_send_params} to @code{_foobar.h} and
+ @code{_foobar.c}. The following example code shows how to send a
+ ``Hello World'' string in the supplemental data handshake message:
+ 
+ @example
+ int 
+ _foobar_supp_recv_params(gnutls_session_t session,const opaque *data,size_t _data_size)
+ @{
+    uint8_t len = (int) _data_size;
+    unsigned char *msg;
+ 
+    msg = (unsigned char *)malloc(len*sizeof(unsigned char));
+    memcpy(msg,data,len);
+    msg[len]='\0';
+ 
+    return len;
+ @}
+ 
+ int 
+ _foobar_supp_send_params(gnutls_session_t session,gnutls_buffer_st *buf)
+ @{
+    unsigned char *msg = "hello world";
+    int len = strlen(msg);
+ 
+    _gnutls_buffer_append_data_prefix(buf,8,msg,(uint8_t) len);
+ 
+    return len;
+ @}
+ @end example
+ 
+ Afterwards, add the new supplemental data handshake message to
+ @code{lib/gnutls_supplemental.c} by adding a new entry to the
+ @code{_gnutls_supplemental[]} structure:
+ 
+ @example
+ gnutls_supplemental_entry _gnutls_supplemental[] = 
+ @{
+   @{"foobar",
+    GNUTLS_SUPPLEMENTAL_FOOBAR_DATA,
+    _foobar_supp_recv_params,
+    address@hidden,
+   @{0, 0, 0, address@hidden
+ @};
+ @end example
+ 
+ You have to include your @code{foobar.h} header file as well:
+ 
+ @example
+ #include "foobar.h"
+ @end example
+ 
+ Lastly, add the new supplemental data type to
+ @code{lib/includes/gnutls/gnutls.h}:
+ 
+ @example
+ typedef enum
+ @{
+     GNUTLS_SUPPLEMENTAL_USER_MAPPING_DATA = 0,
+     GNUTLS_SUPPLEMENTAL_FOOBAR_DATA = 1
+ @} gnutls_supplemental_data_format_type_t;
+ @end example
+ 
  @node Cryptographic Backend
  @section Cryptographic Backend
  Today most new processors, either for embedded or desktop systems