D1/D3/D4 is a connector frequently used in Japan to carry RGB/Component video signals. Rather than have 3 separate YPbPr cables, one cable carries everything.
There are also D-connectors that are available as 'breakout' connectors, one end is a D-connector, other is a YPbPr connector
Sorry Robert, no Blu-Ray Showgirls yet...
But I plan to transfer my favorite D-VHS tapes to BluRay, so we could watch, hmm, let's see...dunno, something cool.