jrc> How about changing the model to 'choice' and requiring one but allowing two jrc> (or multiple) occurrences of optional elements? jrc> something like this maybe?

jrc> <xs:choice minOccurs="1" maxOccurs="2"> jrc> <xs:element name="A" minOccurs="0" maxOccurs="1"/> jrc> <xs:element name="B" minOccurs="0" maxOccurs="1"/> jrc> </xs:choice>

Dosn't it alllow the choice whithout A nor B for their minOccurs=0?

Substition group would do.

Cheers, James