This is probably old hat to XML experts, but it’s new to me–the default values of the minOccurs and maxOccurs attributes of <xs:element>…</xs:element> in XML schemas are both 1 (one). I had a schema definition with minOccurs=”0″ and no value for maxOccurs. In order to get the behavior I assumed was the default, maxOccurs needed to be set to “unbounded”.