The frame type represents a frame or fretboard diagram used together with a chord symbol. The representation is based on the NIFF guitar grid with additional information. The frame type's unplayed attribute indicates what to display above a string that has no associated frame-note element. Typical values are x and the empty string. If the attribute is not present, the display of the unplayed string is application-defined.
The
<frame>element.The frame type represents a frame or fretboard diagram used together with a chord symbol. The representation is based on the NIFF guitar grid with additional information. The frame type's unplayed attribute indicates what to display above a string that has no associated frame-note element. Typical values are x and the empty string. If the attribute is not present, the display of the unplayed string is application-defined.
See
https://www.w3.org/2021/06/musicxml40/musicxml-reference/elements/frame/