Following is a sentence from an article in The New York Times, having a grammar that I could not fathom.
"I would not have minded if Smollett had gotten off relatively lightly— provided, that is, that he had admitted the charges, shown contrition and begged forgiveness."
"that is" in this sentence, seems to be redundant and unnecessary. Besides, how is it possible for "provided that", which implies "if condition", to be separated by "that is"? I have searched the internet about the grammar behind this sentence, but unfortunately, I cannot find the proper grammar, and since my native language is not English I could not comprehend it by myself.