System *sys = dynamic_cast<System *> (sys_span);
Interval_t<int> sri = sys->spanned_rank_interval ();
vector<Grob *> footnote_grobs = sys->get_footnote_grobs_in_range (sri[LEFT], sri[RIGHT]);
System *sys = dynamic_cast<System *> (sys_span);
Interval_t<int> sri = sys->spanned_rank_interval ();
vector<Grob *> footnote_grobs = sys->get_footnote_grobs_in_range (sri[LEFT], sri[RIGHT]);