The id attribute is the QIF id of the point with normal, used for referencing.
Source
<xs:element name="MeasurePoint" type="MeasurePointNominalType" maxOccurs="unbounded"><xs:annotation><xs:documentation>Each MeasurePoint element is an individual nominal measurement point for a feature.</xs:documentation></xs:annotation></xs:element>
<xs:complexType name="PointSetNominalType"><xs:annotation><xs:documentation>The PointSetNominalType defines a set of ordered nominal target measurement points for a feature with a QIF id for referencing.</xs:documentation></xs:annotation><xs:sequence><xs:element name="MeasurePoint" type="MeasurePointNominalType" maxOccurs="unbounded"><xs:annotation><xs:documentation>Each MeasurePoint element is an individual nominal measurement point for a feature.</xs:documentation></xs:annotation></xs:element></xs:sequence><xs:attributeGroup ref="AttrPoint"><xs:annotation><xs:documentation>The AttrPoint attribute group defines accuracies common to all nominal measurement points in the set.</xs:documentation></xs:annotation></xs:attributeGroup><xs:attribute name="n" type="NaturalType" use="required"><xs:annotation><xs:documentation>The required n attribute is the number of nominal points in this set.</xs:documentation></xs:annotation></xs:attribute><xs:attribute name="id" type="QIFIdType" use="required"><xs:annotation><xs:documentation>The id attribute is the QIF id of the nominal point set, used for referencing.</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 nominal points in this set.</xs:documentation></xs:annotation></xs:attribute>
<xs:attribute name="id" type="QIFIdType" use="required"><xs:annotation><xs:documentation>The id attribute is the QIF id of the nominal point set, used for referencing.</xs:documentation></xs:annotation></xs:attribute>