C<value> can be NULL.
+=head2 debug
+
+ debug subcmd 'extraargs ...'
+
+The C<debug> command exposes some internals of
+C<guestfsd> (the guestfs daemon) that runs inside the
+qemu subprocess.
+
+There is no comprehensive help for this command. You have
+to look at the file C<daemon/debug.c> in the libguestfs source
+to find out what you can do.
+
=head2 download
download remotefilename (filename|-)