The optional xId attribute is a reference to the id of a QIF object in an external document. A QIF object in an external QIF document can be referenced by using references to two QIF ids: the id of the external document reference of type ExternalQIFDocumentReferenceType found in the local document and the id of the object found in the external document.
Source
<xs:complexType name="QIFReferenceActiveType"><xs:annotation><xs:documentation>The QIFReferenceActiveType is a reference to a QIFId with defined activity.</xs:documentation></xs:annotation><xs:simpleContent><xs:extension base="QIFReferenceType"><xs:attribute name="active" type="xs:boolean" default="false"><xs:annotation><xs:documentation>The active attribute defines whether the reference is active.</xs:documentation></xs:annotation></xs:attribute></xs:extension></xs:simpleContent></xs:complexType>
<xs:attribute name="active" type="xs:boolean" default="false"><xs:annotation><xs:documentation>The active attribute defines whether the reference is active.</xs:documentation></xs:annotation></xs:attribute>