The Apple Type Services for Unicode Imaging (ATSUI) is the set of services for rendering Unicode-encoded text introduced in Mac OS 8.5 and carried forward into Mac OS X.
ATSUI was replaced by a faster[1] and modern Unicode imaging engine called Core Text in Mac OS X 10.5 (Leopard).
It was officially deprecated with Xcode 4.6, which was released in December 2012: "Source code using ATS APIs will generate warnings while being compiled.
Programmers are instructed to replace all their ATS code (including ATSUI) with CoreText as ATS functionality will be completely removed in future releases of OS X.
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