parser data UPDATE allow action element for actions

Fixes cesnet/netopeer2#1416
diff --git a/src/parser_data.h b/src/parser_data.h
index 1bad5b2..537d6d4 100644
--- a/src/parser_data.h
+++ b/src/parser_data.h
@@ -312,7 +312,7 @@
 enum lyd_type {
     LYD_TYPE_DATA_YANG = 0,     /* generic YANG instance data */
     LYD_TYPE_RPC_YANG,          /* instance of a YANG RPC/action request with only "input" data children,
-                                   including all parents in case of an action */
+                                   including all parents and optional top-level "action" element in case of an action */
     LYD_TYPE_NOTIF_YANG,        /* instance of a YANG notification, including all parents in case of a nested one */
     LYD_TYPE_REPLY_YANG,        /* instance of a YANG RPC/action reply with only "output" data children,
                                    including all parents in case of an action */