The required n attribute is the number of shells in this set.
Source
<xs:complexType name="ShellSetType"><xs:annotation><xs:documentation>The ShellSetType represents a container for storing all model shells.</xs:documentation></xs:annotation><xs:sequence><xs:element ref="Shell" maxOccurs="unbounded"><xs:annotation><xs:documentation>Each Shell element is a model shell.</xs:documentation></xs:annotation></xs:element></xs:sequence><xs:attribute name="n" type="NaturalType" use="required"><xs:annotation><xs:documentation>The required n attribute is the number of shells in this set.</xs:documentation></xs:annotation></xs:attribute></xs:complexType>
<xs:attribute name="n" type="NaturalType" use="required"><xs:annotation><xs:documentation>The required n attribute is the number of shells in this set.</xs:documentation></xs:annotation></xs:attribute>