The backup and forward elements are required to coordinate multiple voices in one part, including music on multiple staves. The forward element is generally used within voices and staves. Duration values should always be positive, and should not cross measure boundaries or mid-measure changes in the divisions value.
The
<forward>element.The backup and forward elements are required to coordinate multiple voices in one part, including music on multiple staves. The forward element is generally used within voices and staves. Duration values should always be positive, and should not cross measure boundaries or mid-measure changes in the divisions value.
See
https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/forward/