Add comments
diff --git a/src/hb-ot-shape-normalize.cc b/src/hb-ot-shape-normalize.cc
index f695c49..6d516c5 100644
--- a/src/hb-ot-shape-normalize.cc
+++ b/src/hb-ot-shape-normalize.cc
@@ -55,6 +55,10 @@
* feature in the font is not adequate, use the precomposed character
* which typically has better mark positioning.
*
+ * - When a font does not support a combining mark, but supports it precomposed
+ * with previous base. This needs the itemizer to have this knowledge too.
+ * We need ot provide assistance to the itemizer.
+ *
* - When a font does not support a character but supports its decomposition,
* well, use the decomposition.
*
