<element name="plane" required="0">
  <description>Plane shape</description>
  <element name="normal" type="vector3" default="0 0 1" required="1">
    <description>Normal direction for the plane</description>
  </element>
  <element name="size" type="vector2d" default="1 1" min="0 0" required="1">
    <description>Length of each side of the plane</description> 
  </element>
</element>
