What should be disallowed in drums?
Arpeggio & Glissando and Clef are likely candidates, but what else? I'm also thinking away from the palette - perhaps Add Note and Add Interval.
A while ago, I filed #11539: Disallow adding key signature to non-pitch percussion
Comments
Also Transpose I think (octave changing too - via keyboard).
I'm not so sure that arpeggios wouldn't find use in a percussion staff - I'm thinking some might want them to notate, for example, direction of stroke on wind chimes. Really, percussion notation uses more, not fewer, symbols, than standard notation, so I'd be loathe to disallow anything, on the assumption that it might turn out to be just what is needed for some particular passage. Except key signatures, which I agree have no place on an unpitched percussion staff. But it,s not uncommon to want to switch from unpitched to pitched percussion within the same score - hopefully the 2.0 instructment change facility allows for that?
Swapping instruments mid-stave is something I hadn't considered in this case.
Maybe in dropping a clef, a prompt could appear that would offer to change the instrument. Not sure what would happen to if you applied one before forthcoming notes - maybe they would be deleted?