The functions ps and def-instrument-set allow some control over the resulting layout of the score (grouping of instruments by brackets etc.), e.g., by using some predefined ensemble "instruments" like :sq for string quartet.
Is it perhaps also possible to somehow set the layout options supported by def-score in this context? For example, would it be possible to specify the music for the left and right hand of a piano separately (i.e. not together in a triple-nested list), but then have both parts notated on a grand staff? Here is an example (not working) -- amended from the ps documentation. How can I define an instrument set such that this score would wrap the two parts below in a grand staff?
(ps 'my-instrument-set :rh '(((s a4 leg d5 leg fs4 leg d5 leg g4 leg d5) (s a4 leg d5 leg fs4 leg d5 leg g4 leg d5) (s a4 leg d5 leg cs5 leg b4 leg a4 leg g4 leg) (s fs4 leg d4 leg e4 leg cs4 leg e d4))) :lh '(((e fs3 d3 e3) (e fs3 d3 e3) (e fs3 g3 a3) (e d3 a2 d2)))) Another example would be the four strings of a string quartet specified separately etc.
I know of course that I could include both parts in a triple nested list for the instrument :p with the gm instrument set, or the strings with the instrument :sq (as demonstrated in the ps documentation). However if possible, I would prefer to specify the left and hand right hand (upper and lower stave) separately, e.g., because I am further processing partial polyphonic scores before they are given to ps (e.g., appending multiple partial scores into a larger score), and for this processing it would help me to know which part is which by its keyword label.