#hb_face_t to work upon
#HB_OT_TAG_GSUB or #HB_OT_TAG_GPOS
The index of the requested script tag
The index of the requested language tag
The index of the requested feature
The #hb_tag_t of the requested feature
true if the feature is found, false otherwise
Fetches the tag of a requested feature index in the given face's GSUB or GPOS table, underneath the specified script and language.