instrument-specific-markup interface

[Carl D. Sorensen]

Both markup fret diagrams and harp pedal markups share the
instrument-specific-markup interface.  The instrument-specific-markup
interface contains fret-diagram-details, harp-pedal-details, size, and
thickness.

Do we need to combine the two interfaces into one
instrument-specific-markup-interface?  This seems strained to me.  I would
prefer to have a

fret-diagram-markup-interface
with
fret-diagram-details, size, thickness

and a

harp-pedal-interface
with
harp-pedal-details, size, thickness

so that the two aren't combined.  I think that will be more clear.

Is there any reason not to do that?

Carl