The prototype definition holds your list of nodes, routes and even more prototypes. Your node definitions may also contain IS syntax. IS associates fields and nodes in your definition with fields and nodes from your prototype declaration. Think of IS as IS EQUAL TO.
Note the material, texture and textureTransform nodes are now defined with the IS syntax as material, texture and textureTransform. This is necessary for the declarations of those fields and nodes to have any meaning when you call the Sony_Appearance node from within the scene graph.