<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
 
   <xs:element name="X">
      <xs:complexType>
          <xs:sequence>
             <xs:element maxOccurs="unbounded" name="a" type="A_TYPE"/>
          </xs:sequence>
      </xs:complexType>
   </xs:element>
  
   <xs:complexType name="A_TYPE">
      <xs:simpleContent>
         <xs:extension base="xs:boolean">
            <xs:attribute name="att" type="xs:boolean"/>
         </xs:extension>
    </xs:simpleContent>
  </xs:complexType>
</xs:schema>