The id attribute is the QIF id of the datum reference frame, used for referencing.
Source
<xs:element name="DatumReferenceFrame" type="DatumReferenceFrameType" maxOccurs="unbounded"><xs:annotation><xs:documentation>Each DatumReferenceFrame element gives information about a datum reference frame.</xs:documentation></xs:annotation></xs:element>
The required n attribute is the number of datum reference frames in the list.
Source
<xs:complexType name="DatumReferenceFramesType"><xs:annotation><xs:documentation>The DatumReferenceFramesType defines a list of datum reference frames.</xs:documentation></xs:annotation><xs:sequence><xs:element name="DatumReferenceFrame" type="DatumReferenceFrameType" maxOccurs="unbounded"><xs:annotation><xs:documentation>Each DatumReferenceFrame element gives information about a datum reference frame.</xs:documentation></xs:annotation></xs:element></xs:sequence><xs:attribute name="n" type="NaturalType" use="required"><xs:annotation><xs:documentation>The required n attribute is the number of datum reference frames in the list.</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 datum reference frames in the list.</xs:documentation></xs:annotation></xs:attribute>