gml:Node represents the 0-dimensional primitive.The optional coboundary of a node (gml:directedEdge) is a sequence of directed edges which are incident on this node. Edges emanating from this node appear in the node coboundary with a negative orientation. If provided, the aggregationType attribute shall have the value "sequence".A node may optionally be realised by a 0-dimensional geometric primitive (gml:pointProperty).
The attribute gml:id supports provision of a handle for the XML element representing a GML Object. Its use is mandatory for all GML objects. It is of XML type ID, so is constrained to be unique in the XML document within which it occurs.
Source
<element name="Node" type="gml:NodeType" substitutionGroup="gml:AbstractTopoPrimitive"><annotation><documentation>gml:Node represents the 0-dimensional primitive. The optional coboundary of a node (gml:directedEdge) is a sequence of directed edges which are incident on this node. Edges emanating from this node appear in the node coboundary with a negative orientation. If provided, the aggregationType attribute shall have the value "sequence". A node may optionally be realised by a 0-dimensional geometric primitive (gml:pointProperty).</documentation></annotation></element>