Given the following XML and related xsd schema, why will XML fail validation if UniqueID is null? Is there a technical reference that explains this?
XML:
<Data xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><UniqueID xsi:nil="true"/></Data>
Partial Schema:
...<xs:element name="UniqueID" maxOccurs="1" minOccurs="0" nillable="true"><xs:simpleType><xs:restriction base="xs:token"><xs:pattern value="[0-9]{10}" /></xs:restriction></xs:simpleType></xs:element>
....