<xs:element name="Extent" type="ExtentType" minOccurs="0"><xs:annotation><xs:documentation>The optional Extent element gives the extent of the surface profile.</xs:documentation></xs:annotation></xs:element>
The id attribute is the QIF id of the characteristic, used for referencing.
Source
<xs:complexType name="SurfaceProfileCharacteristicDefinitionType"><xs:annotation><xs:documentation>The SurfaceProfileCharacteristicDefinitionType defines information that can be common to more than one profile of a surface characteristic.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="ProfileCharacteristicDefinitionBaseType"><xs:sequence><xs:element name="Extent" type="ExtentType" minOccurs="0"><xs:annotation><xs:documentation>The optional Extent element gives the extent of the surface profile.</xs:documentation></xs:annotation></xs:element></xs:sequence></xs:extension></xs:complexContent></xs:complexType>