The FormCharacteristicNominalBaseType is the abstract base type that defines a unique form characteristic nominal. The TargetValue for a form characteristic is zero.
The id attribute is the QIF id of the characteristic, used for referencing.
Source
<xs:complexType name="FormCharacteristicNominalBaseType" abstract="true"><xs:annotation><xs:documentation>The FormCharacteristicNominalBaseType is the abstract base type that defines a unique form characteristic nominal. The TargetValue for a form characteristic is zero.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="GeometricCharacteristicNominalBaseType"/></xs:complexContent></xs:complexType>