XML/XSD: xs:date and nillable

[Mike Hildner]

If I allow a nillable date element like this

<xs:element name="DOB" type="xs:date" nillable="true"/>

how can I write my element so it validates when there is no date - e.g. You don't know the DOB (date of birth)

Using XmlSpy to test, will need to validate with .NET.

I've tried an empty element, "0000-00-00", and just not including the element, nothing works so far.