Cross-staff stems

This snippet shows how to use Span_stem_engraver and \crossStaff to connect stems across staves automatically.

The stem length need not be specified, as the variable distance between note heads and staves is calculated automatically. However, it is important that \crossStaff is applied to the correct voice or staff (i.e., on the opposite side of where a beam is or would be positioned) to get the desired effect.