XML Schema Regex Pattern Question

Is this legal?

<xsd:simpleType name="AGE"><!-- Age -->
  <xsd:restriction base="xsd:string">
    <xsd:pattern value="NN|NB|BB|99|[0-9]{2}" />
    <!-- NN = Under one day (NewNate); NB = New born 1-6 days; BB = Baby 7-364 days; 99 = Over 98 years old -->
  </xsd:restriction>
</xsd:simpleType>

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