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>
The MeasureEvaluateSpecifiedActionType defines an action that means: measure whatever is necessary in order to find CharacteristicMeasurements for the CharacteristicItems whose QIF ids are specified, and find those measurements. For any FeatureItems that are measured, also populate the corresponding FeatureMeasurements with values.
<xs:complexType name="MeasureEvaluateSpecifiedActionType"><xs:annotation><xs:documentation>The MeasureEvaluateSpecifiedActionType defines an action that means: measure whatever is necessary in order to find CharacteristicMeasurements for the CharacteristicItems whose QIF ids are specified, and find those measurements. For any FeatureItems that are measured, also populate the corresponding FeatureMeasurements with values.</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>