+ (flag-style ,symbol? "The style of the flag to be used with
+@code{MetronomeMark}. Available are @code{'modern-straight-flag},
+@code{'old-straight-flag}, @code{flat-flag}, @code{mensural} and
+@code{'default}")
+ (flat-positions ,list? "Flats in key signatures are placed
+within the specified ranges of staff-positions. The general form
+is a list of pairs, with one pair for each type of clef, in order
+of the staff-position at which each clef places C:
+@code{(alto treble tenor soprano baritone mezzosoprano bass)}.
+If the list contains a single element it applies for all clefs.
+A single number in place of a pair sets accidentals within the octave
+ending at that staff-position.")