Clarification on burning process

[Kitna]

I frequently use mastering applications to burn onto rewritable discs.
When burning with Nero, if I attempt to burn onto a DVD+RW that already contains data (no multi-session, finalised disc) it warns me the current disc is not empty and asks if I would like to erase the data first.
With Astroburn it just writes onto the disc.
Is it actually erasing the disc firstly or just writing over the existing data? (is this possible, maybe a TOC wipe?)
Perhaps even a log event that states the disc is being erased might be useful?
Ultimately I would just like some feedback from the application stating what it is doing.

This would also give me the ability to cancel the burn if I inserted a disc I assumed was blank that I didn't want to write over.

Thanks

[chrashoverraid]

would be a very interesting future!
although i can't use it... the burner in my laptop is broken