<group> legal under <extension>?

Hi everyone -

Can someone in the know tell me if the following is legal?

	<xsd:complexType name="foo.extended.type">
		<xsd:complexContent>
			<xsd:extension base="xhtml:form.type">
				<xsd:group ref="foo.extension.content"/>
			</xsd:extension>
		</xsd:complexContent>	
	</xsd:complexType>	

Basically, can I use <group> to extend an element, instead of directly
placing a <sequence>, <choice>, or <all> node underneath?

Seems logical, but maybe I'm missing something (or XML Spy is)...

Thanks,

-Hamish