The notehead-text type represents text that is displayed inside a notehead, as is done in some educational music. It is not needed for the numbers used in tablature or jianpu notation. The presence of a TAB or jianpu clefs is sufficient to indicate that numbers are used. The display-text and accidental-text elements allow display of fully formatted text and accidentals.
The
<notehead-text>element.The notehead-text type represents text that is displayed inside a notehead, as is done in some educational music. It is not needed for the numbers used in tablature or jianpu notation. The presence of a TAB or jianpu clefs is sufficient to indicate that numbers are used. The display-text and accidental-text elements allow display of fully formatted text and accidentals.
See
https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/notehead-text/