How to add an ossia
In the How To for adding an ossia, @Jinx_Dojo added that the staff for the ossia needs to be added in the same instrument citing bug report #104436: Adding staff to instrument in score does not add staff to part; possibly crash involving undo / toggle mmrest. Since this refers to adding a staff to an instrument, such as in a grand staff or linked staff, and the instructions for adding an ossia uses a separate instrument, I don't think it's necessary to add the staff using the same instrument. Since the ossia is an alternate set of notes for an instrument to play it would make sense to use the same instrument, but it will look the same and can be made to sound the same with a different instrument if needed for some reason.
Thoughts?
Comments
I am of the opinion that an ossia should be a staff of the same instrument in most cases. After all, that is exactly what it is. The only possible reason I can see for using a separate instrument is as a workround for the bug. But sure, if someone has some unusual special-case reason to want it, they are welcome to - we just shouldn't be recommending it in general.