+ '())
+
+(ly:add-interface
+ 'fret-diagram-interface
+ "A fret diagram"
+ '(align-dir barre-type dot-color dot-radius finger-code fret-count
+ label-dir number-type size string-count thickness))
+
+(ly:add-interface
+ 'grace-spacing-interface
+ "Keep track of durations in a run of grace notes."
+ '(columns common-shortest-duration))