Silently depressed keys

[Dan Eble]

I’m experimenting with an articulation called \silent that uses a large 
negative midi-extra-velocity property to add a note with minimum velocity to 
the MIDI output.  The purpose is to represent the technique of silently 
depressing keys on a piano so that the strings vibrate in sympathy.  (I’ve hit 
one or two MIDI bugs so far; I wonder how deep they go...)

I would like for the shape of silent note heads to be configurable with a 
context property.  The default would be normal note heads, but I would set them 
to diamonds in PianoStaff following Behind Bars p.338.

If there is any other aspect of the feature I should consider, or if this seems 
like the wrong approach to take, I would be grateful to hear about it.

Regards,
— 
Dan