C<guestfs_set_subprocess_quit_callback>,
C<guestfs_set_launch_done_callback>, C<guestfs_set_close_callback> and
C<guestfs_set_progress_callback> are no longer documented in this
-manual page.
+manual page. Because of the ABI guarantee, the old functions continue
+to work.
Handles generate events when certain things happen, such as log
messages being generated, progress messages during long-running
C<key> is the name to associate with this data, and C<data> is an
arbitrary pointer (which can be C<NULL>). Any previous item with the
-same name is overwritten.
+same key is overwritten.
-You can use any C<key> you want, but names beginning with an
-underscore character are reserved for internal libguestfs purposes
-(for implementing language bindings). It is recommended to prefix the
-name with some unique string to avoid collisions with other users.
+You can use any C<key> you want, but your key should I<not> start with
+an underscore character. Keys beginning with an underscore character
+are reserved for internal libguestfs purposes (eg. for implementing
+language bindings). It is recommended that you prefix the key with
+some unique string to avoid collisions with other users.
To retrieve the pointer, use: