Apple Advanced Typography (AAT) is Apple Inc.'s computer technology for advanced font rendering, supporting internationalization and complex features for typographers, a successor to Apple's little-used QuickDraw GX font technology of the mid-1990s. It is a set of extensions to the TrueType outline font standard, with smartfont features similar to the OpenType font format that was developed by Adobe and Microsoft, and to Graphite. It also incorporates concepts from Adobe's "multiple master" font format, allowing for axes of traits to be defined and morphing of a glyph independently along each of these axes. AAT font features do not alter the underlying typed text; they only affect the characters' representation during glyph conversion. Features Significant features of AAT currently include: Several degrees of ligature control Kashida justification and joiners Cross-stream kerning (required for Nasta'liq Urdu, for example) Indic vowel rearrangement Independently controllable substitution of: Old style figures Small caps and drop caps Swash variants Alternative glyphs: Individual alternatives on a per-glyph basis Wholesale alternatives, such as engraved text Anything else the font designer wants to add Glyph variation axes AAT font features are supported on Mac OS 8.5 and above and all versions of macOS. The cross-platform ICU library provided basic AAT support for left-to-right scripts. HarfBuzz version 2 has added AAT shaping support, an open-source implementation of the technology which Chrome/Chromium as version 72 and LibreOffice as version 6.3 uses it instead of CoreText for rendering macOS AAT fonts in cross-platform way. As of OS X Yosemite and iOS 8, AAT supports language-specific shaping—that is, changing how glyphs are processed depending on the human language they are being used to represent. This support is available through the use of language tags in Core Text. Provision was added at the same time for the relative positioning of two glyphs via anchor points via the ‘kerx’ and ‘ankr’ tables. AAT and OpenType in macOS As of Mac OS X 10.5 Leopard, partial support for OpenType is available. As of 2011, support is limited to Western and Arabic scripts. If a font has AAT tables, they will be used for typography. If the font does not have AAT tables but does have OpenType tables, they will be used to the extent that the system supports them. This means that many OpenType fonts for Western or Middle Eastern scripts can be used without modification on Mac OS X 10.5, but South Asian scripts such as