The required n attribute is the number of plan elements in the list.
Source
<xs:complexType name="UnnumberedPlanElementsType"><xs:annotation><xs:documentation>The UnnumberedPlanElementsType defines a set of plan elements without sequence numbers.</xs:documentation></xs:annotation><xs:sequence><xs:element ref="PlanElement" maxOccurs="unbounded"><xs:annotation><xs:documentation>Each PlanElement element is one member of the set of unnumbered plan elements.</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 plan elements in the list.</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 plan elements in the list.</xs:documentation></xs:annotation></xs:attribute>