⌂ SemiChoirStaff is a ChoirStaff with SpanBars except "|"-type bars

If you wish to typeset |., etc, style spanbars on a ChoirStaff, you can add the span_bar_engraver, and instruct it to omit the |-style bars. In this example a new context, SemiChoirStaff, is created to achieve this.