The required n attribute is the number of Id elements in this array.
Source
<xs:element name="CharacteristicNominalIds" type="ArrayReferenceType"><xs:annotation><xs:documentation>The CharacteristicNominalIds element gives a list of ids of the characteristic nominals in the simultaneous requirement group.</xs:documentation></xs:annotation></xs:element>
<xs:element name="Requirement" type="SimultaneousRequirementEnumType"><xs:annotation><xs:documentation>The Requirement element defines the simultaneous requirement for the group of characteristics.</xs:documentation></xs:annotation></xs:element>
<xs:element name="CompositeLevel" type="CompositeSegmentLowerLevelEnumType" minOccurs="0"><xs:annotation><xs:documentation>The optional CompositeLevel element defines the composite level to which the simultaneous requirement applies.</xs:documentation></xs:annotation></xs:element>
<xs:complexType name="SimultaneousRequirementGroupType"><xs:annotation><xs:documentation>The SimultaneousRequirementGroupType defines a group of characteristics that share a simultaneity requirement.</xs:documentation></xs:annotation><xs:sequence><xs:element name="CharacteristicNominalIds" type="ArrayReferenceType"><xs:annotation><xs:documentation>The CharacteristicNominalIds element gives a list of ids of the characteristic nominals in the simultaneous requirement group.</xs:documentation></xs:annotation></xs:element><xs:element name="Requirement" type="SimultaneousRequirementEnumType"><xs:annotation><xs:documentation>The Requirement element defines the simultaneous requirement for the group of characteristics.</xs:documentation></xs:annotation></xs:element><xs:element name="CompositeLevel" type="CompositeSegmentLowerLevelEnumType" minOccurs="0"><xs:annotation><xs:documentation>The optional CompositeLevel element defines the composite level to which the simultaneous requirement applies.</xs:documentation></xs:annotation></xs:element></xs:sequence></xs:complexType>