<xs:attribute name="class">
    <xs:simpleType>
        <xs:restriction base="xs:token">
            <xs:enumeration value="daemon" />
            <xs:enumeration value="domainname" />
            <xs:enumeration value="etheraddress" />
            <xs:enumeration value="event" />
            <xs:enumeration value="eventhandler" />
            <xs:enumeration value="filesystem" />
            <xs:enumeration value="fqdomainname" />
            <xs:enumeration value="groupname" />
            <xs:enumeration value="ipaddress" />
            <xs:enumeration value="library" />
            <xs:enumeration value="macro" />
            <xs:enumeration value="netmask" />
            <xs:enumeration value="newsgroup" />
            <xs:enumeration value="osname" />
            <xs:enumeration value="process" />
            <xs:enumeration value="protocol" />
            <xs:enumeration value="resource" />
            <xs:enumeration value="server" />
            <xs:enumeration value="service" />
            <xs:enumeration value="systemname" />
            <xs:enumeration value="username" />
        </xs:restriction>
    </xs:simpleType>
</xs:attribute>