HOW IS GREY BOX VERIFICATION DONE

[AAA]

hiii friends...

can any one tell me or explain to how is grey box verification done???
black box and white box is clear but how do we carry on with grey box,
what knowledge is known. can we do the same in only in testbench. we
check the output response the way done in black box, but as per
definition grey box has little knowledge about the design
implementation.

Thanks

Cheers.

Abbs