reg:Vertex 

In order to form polygons, vertices are to be connected with straight line segments. In the case of spherical coordinates: greatcircle segments; if a smallCircle element si present, the vertex and its predecessor are to be connected with a smallcircle, by default in the CoordSys that is referenced; optionally, a pole may be specified (other than the CoordSys pole) that defines the smallcircle system

Element Information

Model

reg:Position , reg:SmallCircle{0,1}
Children: reg:Position, reg:SmallCircle

Source 

<xs:element name="Vertex" type="reg:vertexType" maxOccurs="unbounded">
  <xs:annotation>
    <xs:documentation>In order to form polygons, vertices are to be connected with straight line segments. In the case of spherical coordinates: greatcircle segments; if a smallCircle element si present, the vertex and its predecessor are to be connected with a smallcircle, by default in the CoordSys that is referenced; optionally, a pole may be specified (other than the CoordSys pole) that defines the smallcircle system</xs:documentation>
  </xs:annotation>
</xs:element>

Sample