+The list of all relevant B<NID_*> and B<OBJ_* codes> can be found in
+the source code header files E<lt>openssl/obj_mac.hE<gt> and/or
+E<lt>openssl/objects.hE<gt>.
+
+Applications which could pass invalid NIDs to X509_NAME_get_index_by_NID()
+should check for the return value of -2. Alternatively the NID validity
+can be determined first by checking OBJ_nid2obj(nid) is not NULL.
+