"xs:all" with minOccurs="0" and maxOccurs="unbounded"

Hi,

I am trying to identify a schema for the following structure where,
"struct" elements contain one or more "struct" and/or "field" elements
in any order.

Here are some valid examples:

<struct>
   <field/>
   <field/>
</struct>

<struct>
   <struct>
     <field/>
   </struct>
   <field/>
   <field/>
</struct>

<struct>
   <field/>
   <field/>
   <struct>
     <field/>
   </struct>
   <field/>
   <struct>
     <field/>
   </struct>
   <field/>
</struct>

etc...ad nauseum...

what i really want is:

"xs:all" with minOccurs="0" and maxOccurs="unbounded"

but this isn't allowed cause "xs:all" is intended for exactly one of
each element.

Any one have a valid solution for this schema definition?

Thanks,
Tony.

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