+/* Unwrap an arbitrary void pointer from an opaque OCaml object. */
+#define Voidptr_val(type,rv) ((type *) Field ((rv), 0))
+
+#if PERL4CAML_REFCOUNTING_EXPERIMENTAL
+
+/* Unwrap a custom block. */
+#define Xv_val(rv) (*((void **)Data_custom_val(rv)))
+