In the Hanyu Pinyin official romanization system for Chinese, diacritics are used to mark the tones of the syllables in which the marked vowels occur.In orthography and collation, a letter modified by a diacritic may be treated either as a new, distinct letter or as a letter–diacritic combination.
Usually ä is sorted as equal to æ (ash) and ö is sorted as equal to ø (o-slash).
The shape of the diacritic developed from initially resembling today's acute accent to a long flourish by the 15th century.
With the advent of Roman type it was reduced to the round dot we have today.
Examples are the diaereses in the borrowed French words naïve and Noël, which show that the vowel with the diaeresis mark is pronounced separately from the preceding vowel; the acute and grave accents, which can indicate that a final vowel is to be pronounced, as in saké and poetic breathèd; and the cedilla under the "c" in the borrowed French word façade, which shows it is pronounced .
In Gaelic type, a dot over a consonant indicates lenition of the consonant in question.