Function reduced_measure_places 

pub fn reduced_measure_places(
    chords: &[WeighedChord<'_>],
    others: &[FloatType],
    maximum: usize,
    trim_below: FloatType,
    algorithm: ChordWeight,
) -> Vec<KeptChord>

Which chords of a measure a reduction keeps, and where: music21’s reduceMeasureToNChords read as places rather than as a stream.

Every chord not named is one the reduction drops, and a kept chord takes the time of the chords it stands for – music21’s greedy walk. others is where the measure’s other elements stand, which the evening out of syncopations reads: a chord may take its time from one of those, which changes nothing a score says since none of them sounds.