What is the meaning of "pur sang"?

In the closing of an English L&U question, one of our users, Cerberus, used what I'm sure is a marvelous construction full of history, pur sang, as in:

"...he is trying to argue here why it should mean something other than it does, which is argumentative pur sang."

Now I know "sang" means blood in Latin, and "pur" probably means "in order to" or something, but I don't get the feel of this phrase by breaking it down into its constituents. What does pur sang mean in this context? Is there a particularly famous literary usage?

as a French guy I suppose I can help you resolve this problem.

Originally, pure sang was an expression used to qualify horses whose parents blood had never been mixed with other species.

When used with other concepts, "pure sang" means full, genuine.

In the original quote

which is argumentative pur sang.

Cerberus means that the attitude of the other person is fully, totally argumentative.

It's a French expression meaning pure-blooded (the literal translation) or thoroughbred. In the example, he's saying that it's a quintessential example of being argumentative. I'm not aware of a famous literary usage, but French literature is not my forte.