Unicode compatibility characters

In Unicode and the Universal Character Set, a compatibility character is a character that is encoded solely to maintain round-trip convertibility with other, often older standards. According to the Unicode Glossary:

A character that would not have been encoded except for compatibility and round-trip convertibility with other standards.

Although the term compatibility appears in character names, it is not itself represented as a distinct character property. In practice, the definition is more complex. One of the properties assigned to characters by the Unicode Consortium is decomposition, including compatibility decomposition. More than five thousand characters have a compatibility decomposition mapping that relates the compatibility character to one or more other UCS characters. By assigning a compatibility decomposition to a character, Unicode effectively designates it as a compatibility character.

The reasons for assigning compatibility status vary and are discussed in more detail below. The term decomposition can be confusing, because in some cases a character’s decomposition consists of a single character. In such cases, the decomposition maps one character to another that is approximately—but not canonically—equivalent.