Well, no offense, if your research is based on such vague terminology then inevitably nothing will turn up. It's in no way clear for what purpose and what specification you even need to export your DXFs, what version of AI you are using and so on. You need to be much more specific. That said, currently DXF handling in AI is a nightmare since various such features have been removed, so perhaps consider using another program or different methodology, anyway.
Mylenium