sendbackup: HEADER variable=value

Hi,

The Application API wiki page at "backup command"
http://wiki.zmanda.com/index.php/Application_API/Operations#backup_command

says that one of the messages that can be output on fd3 is:

sendbackup: HEADER variable=value, information that should go
in the amanda header.

Is that implemented? If my 'backup' operation emits a
variable=value in a sendbackup: HEADER line, is there some way
that later on my 'restore' operation can get the value that was
set for that variable?

I could be doing something wrong, but I don't see either an
error logged when my 'backup' emits that line, or anything
added into the dump header.

Was that an old idea that got changed, and it would now be better
to use the server-side statefile for that?  Or just encode the
information somehow in my application's own dump stream so it
will be sure to be available when restoring?

Am I reading the github branches correctly, to think that 3.3.8
and 3.3.9 both support adding to a state file with
'sendbackup: state' and getting it back with
--recover-dump-state-file, but the later mechanisms implementing
state-stream and DAR are not in any stable release yet?

Thanks,
-Chap