+ 'grace-spacing-interface
+ "Keep track of durations in a run of grace notes."
+ '(columns common-shortest-duration))
+
+(ly:add-interface
+ 'instrument-specific-markup-interface
+ "Instrument-specific markup (like fret boards or harp pedal diagrams)."
+ '(fret-diagram-details harp-pedal-details size thickness))
+
+(ly:add-interface
+ 'key-cancellation-interface
+ "A key cancellation."