A whopping 287 pages full of DXF Geek filled fun on the Autodesk DXF (Drawing eXchange Format) structure to allow the exchange of AutoCAD data with other products. I can almost hear the DXF geeks squealing outloud at the fun topics like "Persistent Inter-Object Reference Handles", "Arbitrary Axis Algorithm" and the ever popular "Group Codes". I hear some saying "but DXF files are larger and slower than the DWG", this is true of most any ASCII based file format compared to its binary sibling just look at XML or many other human readable formats compared to binary files. The nice part about a DXF file is that it allows exchange to other systems, programming, or data parsing all in a documented exchange format. DXF has been a good method for over 20 years now.

AutoCAD 2008 DXF v.u.22.1.01 PDF 1.80 MB
More documented DXF versions HERE