Web: Ask the Chicago Manual of Style

"Q. Oh, English-language gurus, is it ever proper to put a question mark and an exclamation mark at the end of a sentence in formal writing? This author is giving me a fit with some of her overkill emphases, and now there is this sentence that has both marks at the end. My everlasting gratitude for letting me know what I should tell this person.

A. In formal writing, we allow both marks only in the event that the author was being physically assaulted while writing. Otherwise, no."

(May I also opine on the vocative case, such as English abstemiates it? "Oh, English-language gurus..." is a bit like, "Hey, Culligan man...!" while "O English-language gurus..." is more like "O Little Town of Bethlehem" or "O Buddha...")