<xs:simpleType name="trill-step"><xs:annotation><xs:documentation>The trill-step type describes the alternating note of trills and mordents for playback, relative to the current note.</xs:documentation></xs:annotation><xs:restriction base="xs:token"><xs:enumeration value="whole"/><xs:enumeration value="half"/><xs:enumeration value="unison"/></xs:restriction></xs:simpleType>