821. Use commas to set off mild interjections or slightly parenthetical expressions.
It was, alas, too late.
Yes, I shall be glad to go.
No, I am sure that is not correct.
It was, therefore, his duty to accept.
I never met him, you know.
822. Use a comma to set off an informal quotation in direct discourse unless the quotation is short and is grammatically incorporated into the sentence.
He said, “I am going home.”
He answered “yes” to my question.
823. Never use a comma between an adjective and the noun it modifies.