<xs:simpleType name="method">
    <xs:annotation>
        <xs:documentation>
      The method attribute of xsl:output:
      Either one of the recognized names "xml", "xhtml", "html", "text",
      or a QName that must include a prefix.
    </xs:documentation>
    </xs:annotation>
    <xs:union>
        <xs:simpleType>
            <xs:restriction base="xs:NCName">
                <xs:enumeration value="xml" />
                <xs:enumeration value="xhtml" />
                <xs:enumeration value="html" />
                <xs:enumeration value="text" />
            </xs:restriction>
        </xs:simpleType>
        <xs:simpleType>
            <xs:restriction base="xsl:QName">
                <xs:pattern value="\c*:\c*" />
            </xs:restriction>
        </xs:simpleType>
    </xs:union>
</xs:simpleType>

• method
• xsl:method