Unicode Explained

applicable syntax. For example, the rules of a programming language might restrict the

character repertoire in identifier names to letters, digits, and one or two other charac-

ters. On the other hand, the underscore (low line) character _ is often usable in names,

and it normally works reliably.

The Misnomer “8-bit ASCII”

The phrase “8-bit ASCII” is used surprisingly often. It follows from the discussion in

the previous section that in reality ASCII is strictly and unambiguously a 7-bit code in

the sense that all code positions are in the range 0–127. It can be, and it usually is,

represented using 8-bit bytes, but with the first bit always zero, or used for other pur-

poses so that it is not part of the encoded form of a character.

The misnomer “8-bit ASCII” most often denotes windows-1252, the 8-bit code defined

by Microsoft for use in the Western world. More generally, 8-bit ASCII is used to refer

to various character codes, which are extensions of ASCII and mutually more or less

incompatible. The character repertoire in such a code contains ASCII as a subset, the

code numbers are in the range 0–256, and the code numbers of ASCII characters equal

their ASCII codes.

ISO 8859 Codes

ISO 8859—or more formally, ISO/IEC 8859—is a family of character code standards.

They were largely developed by Ecma, which distributes ECMA standards that are

equivalent to ISO 8859 standards. ISO 8859 standards are largely oriented toward lan-

guages of European origin.

ISO 8859 codes are widely used on different platforms and in different contexts. For

example, on the Web, ISO 8859-1 was long treated as the default encoding. On Win-

dows, ISO 8859 as such is not used that much, but the corresponding, somewhat ex-

tended Windows encodings are common. In Unix and Linux, ISO 8859 is very com-

mon.

Each ISO 8859 standard tries to address the needs of one or more specific languages

and cultural environment, within the fairly narrow framework of 8-bit structure. This

means that in most cases, you cannot represent multilingual text using any single ISO

8859 encoding.

ISO 8859-1 (ISO Latin 1)

The international standard ISO 8859-1 defines a character repertoire identified as Latin

alphabet No. 1, commonly called ISO Latin 1, as well as a character code for it. The

repertoire contains the ASCII repertoire as a subset, and the code numbers for those

characters are the same as in ASCII. The standard also specifies an encoding, which is

similar to that of ASCII: each code number is presented simply as one octet.

124 | Chapter 3: Character Sets and Encodings