Time modification indicates tuplets, double-note tremolos, and other durational changes. A time-modification element shows how the cumulative, sounding effect of tuplets and double-note tremolos compare to the written note type represented by the type and dot elements. Nested tuplets and other notations that use more detailed information need both the time-modification and tuplet elements to be represented accurately.
The
<time-modification>element.Time modification indicates tuplets, double-note tremolos, and other durational changes. A time-modification element shows how the cumulative, sounding effect of tuplets and double-note tremolos compare to the written note type represented by the type and dot elements. Nested tuplets and other notations that use more detailed information need both the time-modification and tuplet elements to be represented accurately.
See
https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/time-modification/