Cross-staff slurs

For a cross staff slur (also works with any slur) click the first note the press ctrl+click the last note of the slur, then press s to apply the slur. Once the slur is applied you can double click it and drag the various squares that will show up to make it the proper shape.

Also, if you are using cross-staff notation (placing notes in one staff, using Ctrl+Shift+up/down to move them to appear in another), you can actually enter the slurs in any of the usual ways before moving the notes, then the slurs will follow. But if you've already moved the notes, or if the notes aren't cross-staff but actually live on different staves, then the ctrl+click method is best. You could create slur within one staff (ending at some other place), then double click it and drag the end point onto the desired note onto another staff. That's probably the least efficient method, though.

I was wishing this was an automatic feature myself. Maybe it could be. I found it is best to do cross-staff notation before slurring between staffs. However, you can't do cross-staff notation if the instruments are different, so you will have to make the notes and then "ctrl+s" across the staffs. With cross-staff notation you have to manually make the rests for the staff you're crossing to and then make the rests invisible for the cross-staff note(s).