>I would say it is by design -- using a rendering model where commands are immediately interpreted by the printer, the ability to overprint white on top of black would require the *removal* of ink from the paper. Or if we've got opaque white ink... The only way around this would to require a model where the commands are sent to a render buffer before committing to actual ink.

This is what we got already with VFP report engine. There is of course buffered rendering.
Question was not about physical implementation, but more logical.