<xs:simpleType name="month">
    <xs:restriction base="xs:string">
        <xs:enumeration value="January" />
        <xs:enumeration value="February" />
        <xs:enumeration value="March" />
        <xs:enumeration value="April" />
        <xs:enumeration value="May" />
        <xs:enumeration value="June" />
        <xs:enumeration value="July" />
        <xs:enumeration value="August" />
        <xs:enumeration value="September" />
        <xs:enumeration value="October" />
        <xs:enumeration value="November" />
        <xs:enumeration value="December" />
    </xs:restriction>
</xs:simpleType>