Combining Class (Unicode)


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Last updated at 8:08 am UTC on 12 December 2015

From The Unicode Standard, p135

Each character in the Unicode Standard has a combining class associated with it.

The combining class is a numerical value used by
the Canonical Ordering Algorithm
to determine which sequences of combining marks are to be considered canonically equivalent and which are not.

Possible values for the combining class property.

Definition D104

Combining class: A numeric value in the range 0..254 given to each
Unicode code point, formally defined as the property Canonical_Combining_Class.

The combining class for each encoded character in the standard is specified in the file UnicodeData.txt in the Unicode Character Database. Any code point not listed in that data file defaults to \p{Canonical_Combining_Class = 0} (or \p{ccc = 0} for short).
An extracted listing of combining classes, sorted by numeric value, is provided in the file DerivedCombiningClass.txt in the Unicode Character Database.
Only combining marks have a combining class other than zero. Almost all combining marks with a class other than zero are also nonspacing marks, with a few exceptions. Also, not all nonspacing marks have a non-zero combining class. Thus, while the correlation between ^\p{ccc=0] and \p{gc=Mn} is close, it is not exact, and implementations should not depend on the two concepts being identical.

Definition D104

See also