Does the Nero 6 SDK do automatic downspeeding?

Question about the Nero SDK’s ability to detect available and true maximum burn speed.

End-user DVD burners, such as regular Nero, seem to not only check the rating on the DVD, but when the burn starts, they sense if that speed will work out and, if not, the speed is automatically downgraded accordingly.

With the SDK, you can check the “WriteSpeeds” for your drive and, presumably, pick the fastest one. Are those write speeds determined by what the media and drive are rated at, or are is the pre-burn test being done to see what’s realistic before the burn is done?