In contrast to OpenType shaping, AAT shaping does not specify a predefined set of shaping models or a set of supported scripts.

Instead, each AAT font includes a complete set of rules that implement the desired shaping model for the intended script. These rules include finite-state machines to match glyph sequences and the shaping operations to perform.

Notably, AAT shaping rules are expressed for glyphs in the font, not for Unicode codepoints. AAT shaping can perform the same shaping operations used in OpenType shaping, as well as other functions that have not been defined for OpenType shaping.