struct Clef_performer;
struct Column_x_positions;
struct Column_info;
+struct Column_spring;
struct Collision;
struct Collision_engraver;
struct Command_req;
struct Slur;
struct Slur_engraver;
struct Slur_req;
-struct Spacing_req;
+struct Spacing_spanner;
struct Span_bar;
struct Span_score_bar;
struct Span_dynamic_req;
struct Span_req;
struct Spanner;
+struct Spring;
struct Spring_spacer;
struct Staff_bracket;
struct Staff_performer;