xpath FEATURE distinguish between traversed node and its value

... for xpath on schema.
Fixes #1538
diff --git a/src/xpath.h b/src/xpath.h
index 4da73ad..7858508 100644
--- a/src/xpath.h
+++ b/src/xpath.h
@@ -228,10 +228,11 @@
 /* _START and _ATOM values should have grouped values */
 #define LYXP_SET_SCNODE_START         -2 /**< scnode not traversed, currently (the only node) in context */
 #define LYXP_SET_SCNODE_START_USED    -1 /**< scnode not traversed except for the eval start, not currently in the context */
-#define LYXP_SET_SCNODE_ATOM           0 /**< scnode was traversed, but not currently in the context */
-#define LYXP_SET_SCNODE_ATOM_CTX       1 /**< scnode currently in context */
-#define LYXP_SET_SCNODE_ATOM_NEW_CTX   2 /**< scnode in context and just added, so skip it for the current operation */
-#define LYXP_SET_SCNODE_ATOM_PRED_CTX  3 /**< includes any higher value - scnode is not in context because we are in
+#define LYXP_SET_SCNODE_ATOM_NODE      0 /**< scnode was traversed, but not currently in the context */
+#define LYXP_SET_SCNODE_ATOM_VAL       1 /**< scnode was traversed and its value used, but not currently in the context */
+#define LYXP_SET_SCNODE_ATOM_CTX       2 /**< scnode currently in context */
+#define LYXP_SET_SCNODE_ATOM_NEW_CTX   3 /**< scnode in context and just added, so skip it for the current operation */
+#define LYXP_SET_SCNODE_ATOM_PRED_CTX  4 /**< includes any higher value - scnode is not in context because we are in
                                               a predicate and this scnode was used/will be used later */
             int32_t in_ctx; /**< values defined as LYXP_SET_SCNODE_* */
         } *scnodes;