67.5 Coding Systems

A coding system is an object that defines how text containing multiple character sets is encoded into a stream of (typically 8-bit) bytes. The coding system is used to decode the stream into a series of characters (which may be from multiple charsets) when the text is read from a file or process, and is used to encode the text back into the same format when it is written out to a file or process.

For example, many ISO-2022-compliant coding systems (such as Compound Text, which is used for inter-client data under the X Window System) use escape sequences to switch between different charsets – Japanese Kanji, for example, is invoked with ‘ESC $ ( B’; ASCII is invoked with ‘ESC ( B’; and Cyrillic is invoked with ‘ESC - L’. See make-coding-system for more information.

Coding systems are normally identified using a symbol, and the symbol is accepted in place of the actual coding system object whenever a coding system is called for. (This is similar to how faces and charsets work.)

• Coding System Types: Classifying coding systems.
• ISO 2022: An international standard for charsets and encodings.
• EOL Conversion: Dealing with different ways of denoting the end of a line.
• Coding System Properties: Properties of a coding system.
• Basic Coding System Functions: Working with coding systems.
• Coding System Property Functions: Retrieving a coding system's properties.
• Encoding and Decoding Text: Encoding and decoding text.
• Detection of Textual Encoding: Determining how text is encoded.
• Big5 and Shift-JIS Functions: Special functions for these non-standard encodings.
• Predefined Coding Systems: Coding systems implemented by MULE.