The <targetHref> sub-element of the <Update> element specifies the url of the document to which the update should be applied the url can either be a full url or a partial relative url. The url may specify kml documents other than the url of the NetworkLink service, although the document must be from the same server, and must be the result of a HTTP request. Specifcation of local files using a file:// will not work.
The writer supports the specification of targetHref either at the writer level via the TARGET_HREF directive, or the kml_target_href format attribute at the feature level. Using a combination of the kml_document_name, and kml_target_href format attributes will permit the create of multiple KML documents, each of which contains it’s own <NetworkLinkControl> and associated update features.
Note: The OGC KML 2.2 schema specifies that each <NetworkLinkControl> element can contain at most one <Update> element. As such, each kml file can only update a single kml document.