Is ASCII considered a subset of Unicode, or are they disjoint sets?

Joe Sam Shirah

ASCII is a subset of Unicode, although it is almost the other way around: the Unicode Standard team intentionally chose to assign the first 256 Unicode characters to match Latin-1. The first 128 characters of Latin-1 match standard ASCII. This means, among other things, that, if UTF-8 encoding is used, the first 128 Unicode characters are identical to ASCII and the first 256 are identical to Latin-1. Unicode 3.0 is also completely compatible with ISO/IEC 10646-1:2000. For more information, see The Unicode® Standard: A Technical Introduction.