DECLARE_SCHEME_CALLBACK (force_shift_callback, (SCM element));
DECLARE_SCHEME_CALLBACK (calc_positioning_done, (SCM element));
DECLARE_SCHEME_CALLBACK (force_shift_callback_rest, (SCM element, SCM off));
DECLARE_SCHEME_CALLBACK (force_shift_callback, (SCM element));
DECLARE_SCHEME_CALLBACK (calc_positioning_done, (SCM element));
DECLARE_SCHEME_CALLBACK (force_shift_callback_rest, (SCM element, SCM off));