Zalgo text provides a straightforward example of how "reversing a string" is ambiguous and ill-defined: one might conceivably want to transpose "letters" along

Zalgo text provides a straightforward example of how "reversing a string" is ambiguous and ill-defined: one might conceivably want to transpose "letters" along with their respective piles of combining marks, stacked in the same order, not to move combining marks to adjacent letters in a different order. And of course what characters are a mark-bearing letter is application-dependent and there might be collateral requirements (e.g. if the reversed text is meant to be displayed swapping closing and opening delimiters such as parentheses: "(note)" -> ")eton(" or "(eton)" ).