AutoCAD® drawings consist largely of structured containers for database objects. Database objects each have the following:
Optional xdata table, just as entities have had since AutoCAD Release 11.
- Handle whose value is unique to the drawing/DXF file, and is constant for the lifetime of the drawing. This format has existed since AutoCAD Release 10, but as of AutoCAD Release 13, handles are always enabled.
- Optional persistent reactor table.
- Optional ownership pointer to an extension dictionary, which in turn owns subobjects placed in it by an application.
Symbol tables and symbol table records are database objects and, thus, have a handle. They can also have xdata and persistent reactors in their DXF records.