<xs:all> with different elements in any order

Hi all,
   I want to validate an XML instance like following with W3C XML Schema.

<OBJECTS>
  <!-- A & Bs in any order and unbounded. B can be before A also. -->
  <A>ddjhfj</A>
  <B>hghgh</B>
  <!-- more A & Bs -->
</OBJECTS>

I want a Schema like (which is invalid) following.

<xs:element name="OBJECTS">
   <xs:complexType>
       <xs:all>
          <xs:element name="A" type="xs:string" maxOccurs="unbounded" />
          <xs:element name="B" type="xs:string" maxOccurs="unbounded" />
       </xs:all>
    </xs:complexType>
</xs:element>

But this is wrong, because in this Schema maxOccurs can be 0 or 1.

Could somebody please suggest a Schema for this requirement.

-- 
Regards,
Mukul Gandhi