diff --git a/src/hb-face-private.hh b/src/hb-face-private.hh
index c4266fff4..43e7b1cb3 100644
--- a/src/hb-face-private.hh
+++ b/src/hb-face-private.hh
@@ -50,12 +50,16 @@ struct hb_face_t {
   void                      *user_data;
   hb_destroy_func_t          destroy;
 
-  unsigned int index;
-  mutable unsigned int upem;
-  mutable unsigned int num_glyphs;
+  unsigned int index;			/* Face index in a collection, zero-based. */
+  mutable unsigned int upem;		/* Units-per-EM. */
+  mutable unsigned int num_glyphs;	/* Number of glyphs. */
 
-  struct hb_shaper_data_t shaper_data;
+  struct hb_shaper_data_t shaper_data;	/* Various shaper data. */
 
+  /* Various non-shaping data. */
+  /* ... */
+
+  /* Cache */
   struct plan_node_t {
     hb_shape_plan_t *shape_plan;
     plan_node_t *next;