Until there is no way to define in XML Schema that a StringProperty may take specific values from an enumeration. For example, if there is a content type representing a CAR and we want to define a property to hold car's color, we have to provide the following definition

<xs:element name="color"
minOccurs="1"
maxOccurs="1"
bccmsmodel:description="The color of the car"
type="xs:string"/>
where there is no restriction on what the values for the color of the car are.

It would be nice to support the following


<xs:element name="color"
minOccurs="1"
maxOccurs="1"
bccmsmodel:description="The color of the car"
>
   <xs:simpleType>
<xs:restriction base="xs:string">
<xs:enumeration value="RED" />
<xs:enumeration value="BLUE" />
    <xs:enumeration value="GREEN" />
</xs:restriction>
</xs:simpleType>
</xs:element>