Restrict the data type by restricting its attributes : Attribute « XML Schema « XML Tutorial

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<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
  targetNamespace="http://www.java2s.com" xmlns="http://www.java2s.com"
  elementFormDefault="qualified">

  <xs:complexType name="tokenWithLangAndNote">
    <xs:simpleContent>
      <xs:extension base="xs:token">
        <xs:attribute name="lang" type="xs:language" />
        <xs:attribute name="note" type="xs:token" />
      </xs:extension>
    </xs:simpleContent>
  </xs:complexType>

  <xs:element name="title">
    <xs:complexType>
      <xs:simpleContent>
        <xs:restriction base="tokenWithLangAndNote">
          <xs:maxLength value="255" />
          <xs:attribute name="lang">
            <xs:simpleType>
              <xs:restriction base="xs:language">
                <xs:enumeration value="en" />
                <xs:enumeration value="es" />
              </xs:restriction>
            </xs:simpleType>
          </xs:attribute>
        </xs:restriction>
      </xs:simpleContent>
    </xs:complexType>
  </xs:element>

</xs:schema>