ComplexContent with Mixed Construct

The following XML schema construct: 

<xs:complexType name="Car">
                        <xs:complexContent mixed="true">
                                    <xs:extension base="SuperCar">
                                                <xs:sequence>
                                                            <xs:element name="engine" type="xs:string"/>
                                                </xs:sequence>
                                    </xs:extension>
                        </xs:complexContent>
            </xs:complexType>

Maps to:

A mixed complex content can only exist if it extends another complex type that is also labelled as mixed.

See http://www.w3.org/TR/xmlschema11-1/#dcl.ctd.ctcc.common

Note: It is not valid for the mixed construct on complex type and complex content to be different.