Chapter 1 -- DXF Format
Object and Entity Codes
In the DXF format, the definition of objects differs from entities: objects have no graphical representation and entities do. For example, dictionaries are objects not entities. Entities are also referred to as graphical objects while objects are referred to as nongraphical objects.
Entities appear in both the BLOCK and ENTITIES sections of the DXF file. The use of group codes in the two sections is identical.
Some group codes that define an entity always appear; others are optional and appear only if their values differ from the defaults.
Do not write programs that rely on the order given here. The end of an entity is indicated by the next 0 group, which begins the next entity or indicates the end of the section.
NOTE Accommodating DXF files from future releases of AutoCAD will be easier if you write your DXF processing program in a table-driven way, ignore undefined group codes, and make no assumptions about the order of group codes in an entity. With each new AutoCAD release, new group codes will be added to entities to accommodate additional features.