Equivalent ways to declare an element with string content and an attribute

Hi Folks,

Suppose that you want to create a <comment> element. Its content is string data and it has an attribute, xml:lang.

Here is a sample instance:

     <comment xml:lang="en">This is a comment</comment>

One way to declare the <comment> element is as a complexType with simpleContent:

                <xs:element name="comment">
                    <xs:complexType>
                        <xs:simpleContent>
                            <xs:extension base="xs:string">
                                <xs:attribute ref="xml:lang" use="required" />
                            </xs:extension>
                        </xs:simpleContent>
                    </xs:complexType>
                </xs:element>

Interestingly, there is a second way. Declare the <comment> element as a complexType with mixed content:

                <xs:element name="comment">
                    <xs:complexType mixed="true">
                        <xs:sequence/>
                        <xs:attribute ref="xml:lang" use="required" />
                    </xs:complexType>
                </xs:element>

Those are two equivalent ways of declaring an element with string content and an attribute.

Neat!

For the second way, notice the empty <sequence> element. From my reading of section 3.4.2.3.3 (bullet 3 in the mapping summary box) it appears that anything but an empty <sequence> element is an invalid schema. Thus, an empty <choice> or <all> element is invalid. However, when I replace the <sequence/> element with <choice/> or <all/> I get no error. Is my schema validator in error, or am I misinterpreting the specification?

/Roger