NR section 2.1.5:
Divided voices
Using arpeggioBracket to make divisi more visible
The arpeggioBracket can be used to indicate the division of voices where there
are no stems to provide the information. This is often seen in choral music.
This deserves an enhancement ticket. Specifying \arpeggio on a chord that is
not intended to be performed as an arpeggio stinks. Lilypond should
automatically add brackets where the allocation of notes to voices is unclear,
when enabled by a context property.
—
Dan