> Consider this base type (with mode="interleave") and subtype 
> (with mode="none"):
> 
>     <complexType name="Publication" abstract="true">
>         <openContent mode="interleave">
>             <any />
>         </openContent>
>         <sequence>
>             <element name="Title" type="string" />
>             <element name="Author" type="string" />
>             <element name="Date" type="gYear"/>
>         </sequence>
>     </complexType>
> 
>     <complexType name="BookPublication">
>         <complexContent>
>             <extension base="pub:Publication">
>                 <openContent mode="none">
>                     <any />
>                 </openContent>
>                 <sequence>
>                     <element name="ISBN" type="string"/>
>                     <element name="Publisher" type="string"/>
>                 </sequence>
>             </extension>
>         </complexContent>
>     </complexType>
> 

Sorry, I misled you. This schema is not valid: it violates Schema Component
Constraint: Derivation Valid (Extension), clause 1.4.3.2.2.3, which states
in effect that if the base type allows open content, then a type derived
from it by extension must also allow open content.

Regards,

Michael Kay
http://www.saxonica.com/
http://twitter.com/michaelhkay