#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
offset of the first feature tag to retrieve
The array of feature indexes found for the query
Total number of features.
Fetches a list of all features in the specified face's GSUB table or GPOS table, underneath the specified script and language. The list returned will begin at the offset provided.