RM 3 5 2 5 Alternative Character Sets (GNAT Reference Manual)

### 6.6 RM 3.5.2(5): Alternative Character Sets ¶

> “If an implementation supports a mode with alternative interpretations for `Character` and `Wide_Character`, the set of graphic characters of `Character` should nevertheless remain a proper subset of the set of graphic characters of `Wide_Character`. Any character set ‘localizations’ should be reflected in the results of the subprograms defined in the language-defined package `Characters.Handling` (see A.3) available in such a mode. In a mode with an alternative interpretation of `Character`, the implementation should also support a corresponding change in what is a legal `identifier_letter`.”

Not all wide character modes follow this advice, in particular the JIS and IEC modes reflect standard usage in Japan, and in these encoding, the upper half of the Latin-1 set is not part of the wide-character subset, since the most significant bit is used for wide character encoding. However, this only applies to the external forms. Internally there is no such restriction.