The required n attribute is the number of Id elements in this array.
Source
<xs:element name="CharacteristicItemIds" type="ArrayReferenceType"><xs:annotation><xs:documentation>The CharacteristicItemIds element is a list of the QIF ids of characteristic items that are to be evaluated.</xs:documentation></xs:annotation></xs:element>
Complex Type EvaluateSpecifiedCharacteristicsActionType
Annotations
The EvaluateSpecifiedCharacteristicsActionType defines an action that means: find CharacteristicMeasurements for the CharacteristicItems whose QIF ids are specified. Do not measure anything while performing this action. All features that need to be measured in order to evaluate the CharacteristicMeasurements must already be measured.
<xs:complexType name="EvaluateSpecifiedCharacteristicsActionType"><xs:annotation><xs:documentation>The EvaluateSpecifiedCharacteristicsActionType defines an action that means: find CharacteristicMeasurements for the CharacteristicItems whose QIF ids are specified. Do not measure anything while performing this action. All features that need to be measured in order to evaluate the CharacteristicMeasurements must already be measured.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="ActionBaseType"><xs:sequence><xs:element name="CharacteristicItemIds" type="ArrayReferenceType"><xs:annotation><xs:documentation>The CharacteristicItemIds element is a list of the QIF ids of characteristic items that are to be evaluated.</xs:documentation></xs:annotation></xs:element></xs:sequence></xs:extension></xs:complexContent></xs:complexType>