Flow.the_native_string_of: add comment

Author: vouillon

compiler/lib/flow.ml

@@ -415,7 +415,11 @@ let the_string_of ~target info x =
 let the_native_string_of ~target info x =
   match the_const_of ~target info x with
   | Some (NativeString i) -> Some i
-  | Some (String i) -> Some (Native_string.of_bytestring i)
+  | Some (String i) ->
+      (* This function is used to optimize the primitives that access
+         object properties. These primitives are expected to work with
+         OCaml string as well, considered as byte strings. *)
+      Some (Native_string.of_bytestring i)
   | _ -> None
 
 let the_block_contents_of info x =