- number
Integer (>0), measure number.
- notes
List of 'note' objects. Sum of notes durations should be compatible
with the measure time signature
- beats
Integer (>0), time signature is beats/beatType (default 4/4).
- beatType
Integer (>0), time signature is beats/beatType (default 4/4).
- keySignature
Integer, representing the number of flats (<0) or sharps (>0).
- mode
Character, mode. Can be one of major, minor, dorian, phrygian, lydian,
mixolydian, aeolian, ionian, locrian, and none.