PATH Mac OS 8 and 9 Developer Documentation > Text Encoding Conversion Manager
Programming With the Text Encoding Conversion Manager

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Repertoire and Semantics

The notion of character repertoire becomes a bit fuzzy when a single character in one repertoire has a range of interpretations that matches several characters in another repertoire. Consider the following:

• ASCII 0x2D, HYPHEN-MINUS. Unicode has a HYPHEN-MINUS, but also separate HYPHEN and MINUS SIGN characters. In effect the Unicode repertoire has three characters matching the single ASCII character.

• JIS X0208 0x2142, specified as «double vertical line, parallel.» Unicode has separate characters for DOUBLE VERTICAL LINE and PARALLEL TO. There is no single Unicode character that exactly matches the JIS character; each of the Unicode characters matches one interpretation of the JIS character.

Some character encodings explicitly represent presentation forms. All of the forms shown in Figure B-2 , for example, are explicitly encoded in one or another encodings. This also creates a situation where multiple characters in one encoding match a smaller number of characters in another encoding.

Finally, there are many nonstandard additions to various encodings. For example:

• Many vendors have their own versions of Shift-JIS that add characters at various code points that are unused in standard Shift-JIS. These may be treated as separate encodings.

• Users in certain fields, such as law or medicine, may have their own standard set of «gaiji» characters that are added to Shift-JIS using custom fonts. Even without gaiji additions, different fonts on a platform may implement slightly different versions of a character encoding (usually the differences are in less commonly used characters).

• Many encodings permit the addition of user-defined characters in unused code points. A glyph editor may be provided so users can create a custom glyph and assign it to a code point.