Function merge_variant_scores 

pub fn merge_variant_scores(
    a: &Stream,
    v: &Stream,
    variant_name: &str,
) -> Result<Stream>

Merges another version of a score into a copy of it, each part into the part at its place, as merge_variant_measure_streams merges them: music21’s mergeVariantScores.

Errors

Scores of different numbers of parts, or as merge_variant_measure_streams.