The ShapeFeatureDefinitionBaseType is the abstract base type for shape feature definitions. A shape feature definition holds that portion of shape feature nominal information which can be shared among several features, e.g. feature size.
The id attribute is the QIF id of the feature, used for referencing.
Source
<xs:complexType name="ShapeFeatureDefinitionBaseType" abstract="true"><xs:annotation><xs:documentation>The ShapeFeatureDefinitionBaseType is the abstract base type for shape feature definitions. A shape feature definition holds that portion of shape feature nominal information which can be shared among several features, e.g. feature size.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="FeatureDefinitionBaseType"/></xs:complexContent></xs:complexType>