If a program has other metadata not yet supported in the MusicXML format, each type of metadata can go in a miscellaneous-field element. The required name attribute indicates the type of metadata the element content represents.
<xs:complexType name="miscellaneous-field"><xs:annotation><xs:documentation>If a program has other metadata not yet supported in the MusicXML format, each type of metadata can go in a miscellaneous-field element. The required name attribute indicates the type of metadata the element content represents.</xs:documentation></xs:annotation><xs:simpleContent><xs:extension base="xs:string"><xs:attribute name="name" type="xs:token" use="required"/></xs:extension></xs:simpleContent></xs:complexType>