Adding restriction to a complexType

Hello,

Using XML Schema 1.0, I'm having a problem trying to add a restriction to a complexType.  I've got this element definition:

  <xs:element name="productName">
    <xs:simpleType>
      <xs:restriction base="xs:string">
        <xs:minLength value="1"/>
        <xs:maxLength value="255"/>
      </xs:restriction>
    </xs:simpleType>
  </xs:element>

Obviously, I want "productName" to be a character string of 1 to 255 characters.  Now, I'd like to add an element to "productName" - for example "entityRef" (0 to unbounded occurrences).  So, I'd need to change "productName" to <complexType mixed="true">, but I can't figure out how to add the element and maintain the restriction for the overall length of "productName".  This gets me close, but I lose the restriction:

  <xs:element name="productName">
    <xs:complexType mixed="true">
      <xs:choice minOccurs="0" maxOccurs="unbounded">
        <xs:element ref="entityRef"/>
      </xs:choice>
    </xs:complexType>
  </xs:element>

Anyone have a simple solution for maintaining the restriction of 1-255 characters in length?  Or, is this even possible?

Thanks,

Dave Hintz
Siemens