In typesetting, the hook above (Vietnamese: d?u h?i) is a diacritic mark placed on top of vowels in the Vietnamese alphabet. In shape it looks like a tiny question mark without the dot underneath, or a tiny glottal stop (?). For example, a capital A with a hook is "?", and a lower case "u" with a hook is "?". The hook is usually written to the right of the circumflex in conventional Vietnamese orthography. If Vietnamese characters are unavailable, it is often replaced by a question mark after the vowel (VIQR encoding).
This diacritic functions as a tone marker, indicating a "mid falling" tone (h?i): which is "dipping" () in Southern Vietnamese or "falling" () in Northern Vietnamese; see Vietnamese language § Regional variation: Tones. The Southern "dipping" tone is similar to the questioning intonation in English.
The hook above can be used as a tone marker, but is not regarded as part of the alphabet.
Apart from precomposed characters, in multiple scripts, the combining diacritical mark is encoded at ̉ COMBINING HOOK ABOVE (HTML