You said:...

"I thought only the USPTO could validate a patent if challenged, and in a Markman ruling, a judge can validate an infringement claim?"...

The question of Validity of the patent may come up both before USPTO and in a case filed in Federal Court. You are incorrect to think ONLY USPTO can pass judgment on such a question...

A Federal Court may consider the findings by USPTO but is not bound them. On the other hand a RULING by the Federal Court is the Law of the Land and is binding on USPTO and everyone else, especially the defendants in a law suit, with only recourse left being the Appellate process...

Everyone, please take the trouble of reading the Markman Case, and some others discussed here. It will save us a lot of bandwidth once you understand where the Courts are coming from...

GLTA...

Gil...