highlight optionality
diff --git a/skeletons/OBJECT_IDENTIFIER.h b/skeletons/OBJECT_IDENTIFIER.h
index e32ecef..c1c9e2c 100644
--- a/skeletons/OBJECT_IDENTIFIER.h
+++ b/skeletons/OBJECT_IDENTIFIER.h
@@ -105,8 +105,8 @@
* If (oid_txt_length == -1), the strlen() will be invoked to determine the
* size of the (oid_text) string.
*
- * After return, the optional (oid_text_end) is set to the character after
- * the last parsed one. (oid_text_end) is never less than (oid_text).
+ * After return, the optional (opt_oid_text_end) is set to the character after
+ * the last parsed one. (opt_oid_text_end) is never less than (oid_text).
*
* RETURN VALUES:
* -1: Parse error.
@@ -117,7 +117,7 @@
* This is useful for (_arc_slots) value estimation.
*/
int OBJECT_IDENTIFIER_parse_arcs(const char *oid_text, ssize_t oid_txt_length,
- long arcs[], unsigned int arcs_slots, const char **oid_text_end);
+ long arcs[], unsigned int arcs_slots, const char **opt_oid_text_end);
/*
* Internal functions.