This is from The Elements of Style:
If a parenthetic expression is preceded by a conjunction, place the first comma before the conjunction, not after it. He saw us coming, and unaware that we had learned of his treachery, greeted us with a smile.
Do native writers really write in that way? But I think writing in this way is clearer: He saw us coming, and, unaware that we had learned of his treachery, greeted us with a smile.
If a parenthetic expression is preceded by a conjunction, place the first comma before the conjunction, not after it. He saw us coming, and unaware that we had learned of his treachery, greeted us with a smile.
Do native writers really write in that way? But I think writing in this way is clearer: He saw us coming, and, unaware that we had learned of his treachery, greeted us with a smile.