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Each <kml> element may contain zero or one <NetworkLinkControl> elements and zero or one <Document> elements. If a <Document> element and <NetworkLinkControl> element are both present, then the <NetworkLinkControl> element can be used to either update the contents of a document other than it’s sibling <Document>, or it can be used to change certain parameters of the calling <NetworkLink>, such as refresh time, link name, or expiration.