+struct Adobe_font_char_metric;
+struct Adobe_font_metric;
+struct Align_element;
+struct All_font_metrics;
+struct Articulation_req;
+struct Atom;
+struct Audio_column;
+struct Audio_element;
+struct Audio_element_info;
+struct Audio_instrument;
+struct Audio_item;
+struct Audio_key;
+struct Audio_note;
+struct Audio_note_off;
+struct Audio_staff;
+struct Audio_tempo;
+struct Audio_text;
+struct Audio_tie;
+struct Audio_time_signature;
+struct Auto_beam_engraver;
+struct Axis_align_item;
+struct Axis_group;
+struct Axis_group_element;
+struct Axis_group_item;
+struct Axis_group_spanner;
+struct Bar;
+struct Bar_column;
+struct Bar_column_engraver;
+struct Bar_engraver;