This article defines the following terms:

• ASCII character set
• Script system
• 1-byte simple script system
• 1-byte complex script system
• 2-byte script system
• WorldScript I
• WorldScript I

ASCII character set
ASCII is an acronym for American Standard Code for Information Interchange. The 7-bit ASCII character set contains 128 characters, including standard Roman upper and lower case letters, common punctuation marks, and control characters. 8-bit ASCII, sometimes called high ASCII or extended ASCII, contains an additional 128 values, which can be used by foreign writing systems for other characters that are not available in the standard 128 characters.


Script system
A script system is a collection of software facilities that provide for the representation of a specific writing system. It consists of a set of keyboard resources, a set of international resources, any fonts, and possibly a script system extension (1-byte or 2-byte). Script systems include Roman, Japanese, Arabic, Traditional Chinese, Simplified Chinese, Hebrew, Cyrillic, and Korean. Types of script systems include 1-byte simple, 1-byte complex, and 2-byte (also called 16-bit).


1-byte simple script system
A 1-byte simple script system supports a writing system with a small character set (requires only 1-byte characters), has a left-to-right text direction only, and that is non-contextual. The Roman script system is an example of a 1-byte simple script system.


1-byte complex script system
A 1-byte complex script system supports a writing system with a small character set (requires only 1-byte characters), but that is characterized by bidirectional or contextual text (characters whose appearance may be different, relative to their position to other characters). Arabic and Hebrew are examples of complex 1-byte script systems.


2-byte script system
A 2-byte script system supports a writing system with a large character set (requires 2-byte characters) and requires sophisticated procedures for character input. Japanese, Chinese, and Korean are examples of 2-byte script systems. 2-byte characters, such as Kanji, consist of two 8-bit (1-byte) characters which, placed beside each other, are displayed by the System as a single character.


WorldScript I
WorldScript I is an extension to the Mac OS that is used for all 1-byte complex script systems. Code in the extension reads tables in the script system's international resources to provide the proper text manipulation and formatting for that script. Simple 1-byte script systems do not need to use WorldScript I.


WorldScript II
WorldScript II is an extension to the Mac OS that is used for all 2-byte script systems. Code in the extension reads tables in the script system's international resources to provide the proper text manipulation and formatting for that script. WorldScript II functionality has been incorporated into Mac OS 9 and is no longer a separate extension.

Parts of this information were compiled from Apple's technical documentation, Inside Macintosh: Text.