<xs:attribute name="context" use="optional">
    <xs:annotation>
        <xs:documentation>An indication of whether this line is a current line, or a repeat of a special-interest line from the past.</xs:documentation>
    </xs:annotation>
    <xs:simpleType id="context">
        <xs:restriction base="xs:string">
            <xs:enumeration id="contextOpening" value="opening" />
            <xs:enumeration id="contextClosing" value="closing" />
            <xs:enumeration id="contextCurrent" value="current" />
        </xs:restriction>
    </xs:simpleType>
</xs:attribute>