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

	<xs:element name="foo" type="baseType"/>

	<xs:complexType name="baseType">

		<xs:all>

			<xs:element name="bar" type="derivedType" minOccurs="0"/>

		</xs:all>

		<xs:attribute name="attrA" type="xs:string" use="required"/>

	</xs:complexType>

	<xs:complexType name="derivedType">

		<xs:complexContent>

			<xs:extension base="baseType">

				<xs:attribute name="attrB" type="xs:string" use="required"/>

			</xs:extension>

		</xs:complexContent>

	</xs:complexType>

</xs:schema>