Mine

        <xs:element name="option">
                <xs:complexType>
                        <xs:simpleContent>
                                <xs:restriction base="xs:string">
                                        <xs:pattern value=".+"/>
                                        <xs:attribute name="key" type="xs:string"/>
                                </xs:restriction>
                        </xs:simpleContent>
                 </xs:complexType>
        </xs:element>

would validate this:
<option key='foo'>bar</option>