⌂ Grouping contexts

In polyphonic notation, many voices can share a staff: In this situation, the accidentals and staff are shared, but the stems, slurs, beams, etc., are private to each voice. Hence, engravers should be grouped. The engravers for note head, stems, slurs, etc., go into a group called Voice context, while the engravers for key, accidental, bar, etc., go into a group called Staff context. In the case of polyphony, a single Staff context contains more than one Voice context. Similarly, more Staff contexts can be put into a single Score context.