simultaneous music, or the alternatives of repeated music.")
(elements-callback ,procedure? "Return a list of children, for use by
a sequential iterator. Takes a single music parameter.")
- (expected-beam-count ,integer? "Expected number of non-tremolo beams
-in a tremolo repeat.")
(figure ,integer? "A bass figure.")
(force-accidental ,boolean? "If set, a cautionary accidental should