That way AutoCAD is able to call the corresponding routines when a user-defined object is touched. For data exchange, this section is of little value. The Objects section is a bit inappropriately named because graphical entities in DXF have always been objects. What's new is that DXF can now contain graphical objects and nongraphical objects. Nongraphical entities are stored in the Objects section.
Nongraphical objects can be anything from wallpaper catalogs to a project accounting database.
All nongraphical objects are application-defined and therefore have a corresponding definition in the Classes section. File Size DXF has always been criticized for being a fat file format. With Release 13 DXF, file size will be even more important. The object-oriented approach within AutoCAD introduces a family history to each and every drawing entity. Listing 2 and listing 3 show examples of an insert entity and a layer description.