hb-graphite2
gr_face * hb_graphite2_face_get_gr_face (hb_face_t *face);
hb_face_t *face
gr_font * hb_graphite2_font_get_gr_font (hb_font_t *font);
hb_font_t *font
#define HB_GRAPHITE2_TAG_SILF HB_TAG('S','i','l','f')