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The list of OpenType features along with their specifications is listed here :
I'm having an hard time determining who this document is intended for especially when it comes to the "Feature interaction" field.
For example, I paste here the documentation for hlig (historical ligatures)
Friendly name: Historical Ligatures
Registered by: Microsoft
Function: Some ligatures were in common use in the past, but appear anachronistic today. Some fonts include the historical forms as alternates, so they can be used for a 'period' effect. This feature replaces the default (current) forms with the historical alternates.
Example: The user applies this feature using Palatino Linotype, and historic ligatures are formed for all long s forms, including: long s+t, long s+b, long s+h, long s+k, and several others.
Recommended implementation: The hlig table maps default ligatures and character combinations to corresponding historical ligatures (GSUB lookup type 1).
Application interface: For GIDs found in the hlig coverage table, the application passes the GIDs to the hlig table and gets back new GIDs.
UI suggestion: This feature should be off by default.
Script/language sensitivity: None.
Feature interaction: This feature overrides the results of all other features.
The following is clear to me :
"Function" is intended to be read, understood and complied to by the font designer.
"Application interface" is intended to be for opentype shaping engine like Uniscribe or DirectWrite or perhaps applications that interpret themselves the opentype tables.
"UI suggestion" is for the consuming applications like InDesign, Microsoft Word, etc...
"Script/language sensitivity" I think this is for the font designer to limit the application of this feature only to certain languages.
"Feature interaction" No idea : should it be the shaping engine that takes care of that, the consuming applications or the font designer?!!? Does anyone know?
For hlig, it says : "This feature overrides the results of all other features." What does this means and who is responsible for enforcing it?