Ron...

"The issue of validity is a theshold requirement of any patent case."

The word validity, is it an issue in a Markman hearing?

You say it's not an issue, however, the material Minister provided notes that it is, or the word validity is used out of context. Meaning, as you note, Markman is not utilized to weigh validity but infringement, however in the process it does involve degrees of assessment where validity must surface.

Where is the threshold requirement established?

doni