<Libraries> as Organizers
<Libraries> exist to organize specific classes of objects that are referenced throughout the transmittal: <Models>, <Images>, <Attribute Set Tables>, <Color Tables>, <Sounds>, <Symbols>, and <Data Tables>.
All objects whose classes are organized by <Libraries>, except <Data Table> objects, are required to belong to a <Library>.
Objects within a <Library> are referenced by means of objects belonging to special instance classes, e.g. <Geometry Model Instance>, <Image Mapping Function>, <Color Index>.