Kind of an edge case and it can be solved with editing the way it's displayed in Musescore and the generated MXL, but consider the following example for Clementi, Op 36, No 2, 2nd Movement, 7th & 8th Measure (Measure 68=69 in the app),.
The original sheet music has both hands written with Cross Staff notation all in the bass clef:
In Musescore, it's transcribed the same way, with Voice 1 of the Treble Clef displayed on the bass clef using Ctrl-Alt-Down Arrow (Ctrl-Alt-Up Arrow flips it back).
In the MusicXML, this right hand part ends up being Voice 1 Staff 2 and the left hand is Voice 5 Staff 2. In the app, it then assigns that all to the left hand as I believe it's using the Staff as the determination.
I'm not sure what OSMD exposes, but for Musescore files the right hand would technically be Voices 1-4 and left hand Voices 5-8 regardless of the staff it ends up on. So if you could assign it by Voice, that would be a more granular way of handling it (but maybe not always consistent if the source is from another notation app or there are more than 4 voices per hand, etc.)
It can get solved by just editing the Musescore file to move it all to the treble clef (Ctrl-Alt-Up Arrow for those notes):
That works for this example, but if everything were an octave lower, you'd also have to change the staff to bass clef for it to be reasonable to display the notes.
I don't know if it's worth a lot of rejiggering, but if there was a way to have an advanced staff mapping that was by voice, one could control it that way. Like being able to set Left Hand to Voices 5,6,7,8 and Right Hand to Voices 1,2,3,4. Anyway, just wanted to put it out there as I noticed it and it does require some editing of the file to get the app to handle it from the way the MusicXML is set up. But it might not be worth the effort.
Here is the original MXL with Cross Staff and then my edited version which the app then handles correctly for left/right hand assignment.
Clementi_Six_Sonatinas_for_Piano_Op_36 - No. 2_edit CrossStaff.zip
Kind of an edge case and it can be solved with editing the way it's displayed in Musescore and the generated MXL, but consider the following example for Clementi, Op 36, No 2, 2nd Movement, 7th & 8th Measure (Measure 68=69 in the app),.
The original sheet music has both hands written with Cross Staff notation all in the bass clef:
In Musescore, it's transcribed the same way, with Voice 1 of the Treble Clef displayed on the bass clef using Ctrl-Alt-Down Arrow (Ctrl-Alt-Up Arrow flips it back).
In the MusicXML, this right hand part ends up being Voice 1 Staff 2 and the left hand is Voice 5 Staff 2. In the app, it then assigns that all to the left hand as I believe it's using the Staff as the determination.
I'm not sure what OSMD exposes, but for Musescore files the right hand would technically be Voices 1-4 and left hand Voices 5-8 regardless of the staff it ends up on. So if you could assign it by Voice, that would be a more granular way of handling it (but maybe not always consistent if the source is from another notation app or there are more than 4 voices per hand, etc.)
It can get solved by just editing the Musescore file to move it all to the treble clef (Ctrl-Alt-Up Arrow for those notes):
That works for this example, but if everything were an octave lower, you'd also have to change the staff to bass clef for it to be reasonable to display the notes.
I don't know if it's worth a lot of rejiggering, but if there was a way to have an advanced staff mapping that was by voice, one could control it that way. Like being able to set Left Hand to Voices 5,6,7,8 and Right Hand to Voices 1,2,3,4. Anyway, just wanted to put it out there as I noticed it and it does require some editing of the file to get the app to handle it from the way the MusicXML is set up. But it might not be worth the effort.
Here is the original MXL with Cross Staff and then my edited version which the app then handles correctly for left/right hand assignment.
Clementi_Six_Sonatinas_for_Piano_Op_36 - No. 2_edit CrossStaff.zip