<xsd:attribute name="format" use="required"> <xsd:simpleType> <xsd:restriction base="xsd:string"> <!-- base="xsd:NMTOKEN" "text/xml" is invalid wrt NMTOKEN --> <xsd:enumeration value="text/xml" /> <xsd:enumeration value="text/html" /> <xsd:enumeration value="text/sgml" /> <xsd:enumeration value="text/plain" /> </xsd:restriction> </xsd:simpleType> </xsd:attribute>