Three equivalent ways to specify an unconstrained data type ... are there others?

Hi Folks,

Below are declarations of three elements, E1, E2, and E3. All three elements have the same data type: an unconstrained string. All other data types (boolean, integer, etc.) can be similarly specified. Thus there are 3 ways to specify the same thing for every built-in data type.

Can you think of any other ways to specify an unconstrained data type?

    <xs:element name="E1" type="xs:string" />  
    
    <xs:element name="E2" type="string-equivalent-1" /> 
    
    <xs:element name="E3" type="string-equivalent-2" />
    
    <xs:complexType name="string-equivalent-1">
        <xs:simpleContent>
            <xs:extension base="xs:string" />
        </xs:simpleContent>
    </xs:complexType>
    
    <xs:simpleType name="string-equivalent-2">
        <xs:restriction base="xs:string" />
    </xs:simpleType>

/Roger