XeTeX is a TeX typesetting engine using Unicode and supporting modern font technologies such as OpenType, TrueType or Apple Advanced Typography (AAT), including OpenType mathematics fonts. XeTeX supports many extensions that reflect its origins in linguistic research; it also supports micro-typography (as available in pdfTeX). XeTeX was developed by the SIL (the first version was specifically developed for those studying linguistics, and using Macintosh computers). XeTeX’s immediate output is an extended variant of DVI format, which is ordinarily processed by a tightly bound processor (called xdvipdfmx), that produces PDF. XeTeX is developed as a part of TeX Live; documentation has arisen separately. Source code is available from ctan:/systems/texlive/source.