The bass-alter element represents the chromatic alteration of the bass of the current chord within the harmony element. In some chord styles, the text for the bass-step element may include bass-alter information. In that case, the print-object attribute of the bass-alter element can be set to no. The location attribute indicates whether the alteration should appear to the left or the right of the bass-step; it is right if not specified.
The
<bass-alter>element.The bass-alter element represents the chromatic alteration of the bass of the current chord within the harmony element. In some chord styles, the text for the bass-step element may include bass-alter information. In that case, the print-object attribute of the bass-alter element can be set to no. The location attribute indicates whether the alteration should appear to the left or the right of the bass-step; it is right if not specified.
See
https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/bass-alter/