A union simple type specifies a union of atomic simple type values.
Example:
<xs:simpleType name="size"> <xs:union memberTypes="xs:integer"> <xs:simpleType> <xs:restriction base="xs:string"> <xs:enumeration value="small"/> <xs:enumeration value="medium"/> <xs:enumeration value="large"/> </xs:restriction> </xs:simpleType> </xs:union> </xs:simpleType>