Starting with version 7.1, Apple unified the implementation of non-Roman script systems in a programming interface called WorldScript. WorldScript I was used for all one-byte character sets and WorldScript II for two-byte sets. Support for new script systems was added by so-called Language Kits. Some kits were provided with foreign versions of the system software, and others were sold by Apple and third parties. Application support for WorldScript was not universal, since building in support was a significant task.
In 8.5, full Unicode support was added to Mac OS through an API called ATSUI. However, WorldScript remained the dominant technology for international text until Mac OS X, because of limited application support for ATSUI.