The instrument type distinguishes between score-instrument elements in a score-part. The id attribute is an IDREF back to the score-instrument ID. If multiple score-instruments are specified in a score-part, there should be an instrument element for each note in the part. Notes that are shared between multiple score-instruments can have more than one instrument element.
The
<instrument>element.The instrument type distinguishes between score-instrument elements in a score-part. The id attribute is an IDREF back to the score-instrument ID. If multiple score-instruments are specified in a score-part, there should be an instrument element for each note in the part. Notes that are shared between multiple score-instruments can have more than one instrument element.
See
https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/instrument/