Programming Tutorials

What are combining characters?

By: Emiley J. Printer Friendly Format    

Some code points in UCS have been assigned to combining characters. These are similar to the non-spacing accent keys on a typewriter. A combining character is not a full character by itself. It is an accent or other diacritical mark that is added to the previous character. This way, it is possible to place any accent on any character. The most important accented characters, like those used in the orthographies of common languages, have codes of their own in UCS to ensure backwards compatibility with older character sets. They are known as precomposed characters. Precomposed characters are available in UCS for backwards compatibility with older encodings that have no combining characters, such as ISO 8859. The combining-character mechanism allows one to add accents and other diacritical marks to any character. This is especially important for scientific notations such as mathematical formulae and the International Phonetic Alphabet, where any possible combination of a base character and one or several diacritical marks could be needed.

Combining characters follow the character which they modify. For example, the German umlaut character Ä (“Latin capital letter A with diaeresis”) can either be represented by the precomposed UCS code U+00C4, or alternatively by the combination of a normal “Latin capital letter A” followed by a “combining diaeresis”: U+0041 U+0308. Several combining characters can be applied when it is necessary to stack multiple accents or add combining marks both above and below the base character. The Thai script, for example, needs up to two combining characters on a single base character.