Ultegra 6700 compatibility

Hi all,
Are Ultegra 6700 shifters compatible with 6600 F/R derailleurs?

Are there other things that are incompatible?

If following in the footsteps of 7900(which it probably does), 6700 shifters ARE compatible wit the 6600 rear derailleur, NOT compatible with the 6600 front derailleur and 'maybe' not compatible with 6600 brake calipers.

I also wonder if 6700 is the precursor to a Ui2(electronic ultegra) group?

I chanced upon a website which described the 6700 shifters as B level compatible with 6600 ...

Not entirely sure what B level compatible means, but another website which I cant find anymore "elaborated" this to mean fully compatible, but not designed for 6600. What does that even mean?

Beats me. New shifter innards. I doubt they will be different than 7900. Plus, is there a 6703? There isn't a 7903(triple, that is).

YES 6700 shifter are compatible with 6600 components - I have recently installed the 6700 shifters with my normal 6600 Ultegra SL delrailleurs and brakes. I have already done 1 race and some training rides and all functioning 100%.