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This question might be better addressed here:
http://forums.autodesk.com/t5/Visual-LISP-AutoLISP-and-General/bd-p/130
There is also DXF reference in Help (example from 2013):
http://docs.autodesk.com/ACD/2013/ENU/files/GUID-2602B0FB-02E4-4B9A-B03C-B1D904753D34.htm