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I am new to this board and this is my first post. I am currently working on an "Old Style" Greek font, which will include several historic ligatures. I is quite obvious fact, that many of the Greek ligatures are context-dependent: for example, there are usual abbreviations for some common conjunctions or word endings which should not be used in other cases (i. e. when the same sequence of letters occurs at the middle of a word). However, the OpenType specification seems to provide only one feature specially intended for contextual ligatures (namely 'clig'), and most OpenType renderers enable this feature by default, which, of course, is not exactly that I want. On the other hand, the recommended implementation for the 'hlig' feature is GSUB lookup type 1, i. e. plain ligature substitution.
So I am wondering, which feature tag should I use for historical context-dependent ligatures, if I would like them to be disabled in normal contexts? Can anybody suggest me a proper solution?