Although the KML specification permits multiple child elements of the <kml> element, Google Earth, and many other applications only support a single child element. The most common child element is <Document>, and the default behavior of the KML writer is to create a <Document> element that contains the rest of the dataset's features.
The KML writer's default behavior is sufficient for most users, however there is occasionally a need for alternative root-level elements. The KML writer supports requirement via the OMIT_DOCUMENT_ELEMENT directive. If set to yes', the writer will skip writing the <Document> element, and write the child element of the document as the child of the <kml> element.
Note The Document can only have 1 root element, which can be a folder that can in turn contain other elements.