<?xml version="1.0" encoding="ISO-8859-1" ?>

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">

  <xs:element name="foo">
    <xs:complexType>
        <xs:choice minOccurs="0" maxOccurs="unbounded">
        
          <xs:element name="barA"  >
            <xs:complexType>            
              <xs:attribute name="attr" type="xs:string" use="required" />                            
            </xs:complexType>
          </xs:element>
          
          <xs:element name="barB" >
            <xs:complexType>
              <xs:attribute name="attr" type="xs:string" use="optional" />
            </xs:complexType>  
          </xs:element>
          
          <xs:element name="barC" >
            <xs:complexType>
              <xs:attribute name="attr" type="xs:string" use="prohibited" />
            </xs:complexType>  
          </xs:element>
          
        </xs:choice>
    </xs:complexType>
  </xs:element>

</xs:schema>