AutoCAD.
drawings consist largely of structured containers for database
objects. Database objects each have the following features:
A 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, and as of AutoCAD Release 13, handles are
always enabled.
An optional xdata table, as entities have had since AutoCAD
Release 11.
An optional persistent reactor table.
An 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.
