The gYear datatype represents a Gregorian year : gYear « XML Schema « XML Tutorial

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3. gYear

<!-- schema -->
<xsd:element name="interval">
  <xsd:simpleType>
   <xsd:restriction base="xsd:gYear">
    <xsd:minInclusive value="1776"/>
    <xsd:maxInclusive value="1976"/>
   </xsd:restriction>
  </xsd:simpleType>
</xsd:element>
<!-- instance document -->
<interval>1842</interval>