Invalid: derivation of complex type by restriction of simple type not allowed

Hello!

In my schema I have the following:

<xs:complexType name="textareaType">
        <xs:simpleContent>
                <xs:restriction base="xs:string">
                        <xs:attribute ref="label" use="required" />
                </xs:restriction>
        </xs:simpleContent>
</xs:complexType>

But W3C Schema validator tells me there is an error (derivation of
complex type by restriction of simple type not allowed), even if
w3schools writes, that this should be valid code (http://
www.w3schools.com/schema/schema_complex_text.asp).
I also checked the original Schema reference (http://www.w3.org/TR/
xmlschema-1/), that points out: "Note that either <restriction> or
<extension> must be chosen as the content of <simpleContent>."
When I replace restriction by extension everything works fine. But I
want to restrict the element type in a further step.
Any help?

Best regards,
Kai