All visible objects are defined inside a Shape node. This node has two
fields: appearance and geometry .
The appearance field specifies an Appearance
node which is used to define color, textures and so on to be applied to
the geometry, the geometry field indicates which shape is to be
drawn.
The syntax is as follows:
Shape {
appearance NULL
geometry NULL
}
The appearance field is optional, if nothing is said the default
values will be used.
the value for the geometry field may be any of the following Nodes: