Function notes_within_duration 

pub fn notes_within_duration(
    container: &Stream,
    index: usize,
    total: FloatType,
) -> Vec<StreamElement>

The notes, rests and chords from one on, as many as fit in a length, each a copy: music21’s getNotesWithinDuration, read from the stream directly holding the first.

Nothing where the first is longer than the length; else it and each that follows it in its stream while the length left holds it.