This article is from the Programming VCOMM FAQ, by firstname.lastname@example.org (Taed Nelson) with numerous contributions by others.
There is no documentation on these functions.
Serial.vxd doesn't handle the error conditions in these functions correctly.
For example, PortGetCommConfig returns TRUE in all cases, even if dwSize is
less than the size of the Win32 DCB structure (see serfunc.asm module).