OpenType Layout feature classification
OpenType Layout features allow for orthographically correct display of complex scripts such as Arabic and Indic and provide a mechanism for the user to apply advanced typographic formatting to text. They are used in the SFNT GSUB and GPOS tables.
This document contains a useful classification of OpenType Layout feature tags. It is based on the OpenType spec version 1.6, with some additional entries about removed features and Microsoft-only Math features related to the MATH OpenType table.
This document is very technical in nature, and is primarily aimed at software developers who wish to implement user interfaces for applying OpenType Layout features in applications.