Which and That
Can we just agree that “which” and “that” are pretty much interchangable? If you’re relying on a modern audience to be able to perceive the difference in meaning between restrictive and non-restrictive clauses [link to http://home.earthlink.net/~llica/wichthat.htm no longer works], you’ve pretty much already lost.
Which, as they say, makes a mockery of that rule.
Alternately, “That, as they say, makes a mockery of that rule.”
Alternately, “That, as they say, makes a mockery of which rule.”
I think we may be taking this too far.
As the say, “That which makes no difference, does not matter.”