diff --git a/include/vtype.h b/include/vtype.h
index 7815c82..dca09a8 100644
--- a/include/vtype.h
+++ b/include/vtype.h
@@ -99,26 +99,26 @@ extern int map_compare(const vtype_map* s0, const vtype_map* s1)          LIBCDS
 extern int vset_compare(const vtype_set* s0, const vtype_set* s1)         LIBCDSB_cmpattr__;
 
 /* Copy string to another */
-extern vtype_string string_copy(const vtype_string* x) LIBCDSB_cpyattr__;
+extern vtype_string string_copy(const vtype_string* s) LIBCDSB_cpyattr__;
 /* Copy array to another */
-extern vtype_array array_copy(const vtype_array* x)    LIBCDSB_cpyattr__;
+extern vtype_array array_copy(const vtype_array* s)    LIBCDSB_cpyattr__;
 /* Copy list to another */
-extern vtype_list list_copy(const vtype_list* x)       LIBCDSB_cpyattr__;
+extern vtype_list list_copy(const vtype_list* s)       LIBCDSB_cpyattr__;
 /* Copy map to another */
-extern vtype_map map_copy(const vtype_map* x)          LIBCDSB_cpyattr__;
+extern vtype_map map_copy(const vtype_map* s)          LIBCDSB_cpyattr__;
 /* Copy set to another */
-extern vtype_set vset_copy(const vtype_set* x)         LIBCDSB_cpyattr__;
+extern vtype_set vset_copy(const vtype_set* s)         LIBCDSB_cpyattr__;
 
 /* Duplicate string memory block */
-extern vtype_string* string_duplicate(const vtype_string* x) LIBCDSB_dupattr__;
+extern vtype_string* string_duplicate(const vtype_string* s) LIBCDSB_dupattr__;
 /* Duplicate array memory block */
-extern vtype_array* array_duplicate(const vtype_array* x)    LIBCDSB_dupattr__;
+extern vtype_array* array_duplicate(const vtype_array* s)    LIBCDSB_dupattr__;
 /* Duplicate list memory block */
-extern vtype_list* list_duplicate(const vtype_list* x)       LIBCDSB_dupattr__;
+extern vtype_list* list_duplicate(const vtype_list* s)       LIBCDSB_dupattr__;
 /* Duplicate map memory block */
-extern vtype_map* map_duplicate(const vtype_map* x)          LIBCDSB_dupattr__;
+extern vtype_map* map_duplicate(const vtype_map* s)          LIBCDSB_dupattr__;
 /* Duplicate set memory block */
-extern vtype_set* vset_duplicate(const vtype_set* x)         LIBCDSB_dupattr__;
+extern vtype_set* vset_duplicate(const vtype_set* s)         LIBCDSB_dupattr__;
 
 /* Copy string and store result to the memory block */
 extern void string_copy_init(vtype_string* x, const vtype_string* s) LIBCDSB_nn12__;
diff --git a/src/__internal/include.h b/src/__internal/include.h
index 1844919..25d00e9 100644
--- a/src/__internal/include.h
+++ b/src/__internal/include.h
@@ -58,6 +58,7 @@ typedef vtype_kvpair    kvp_t;
 typedef vtype_iterator iter_t;
 
 typedef enum {
+    VF_UNDEFINED  = 0x00,
     VF_WRITEABLE  = 0x01,
     VF_CHANGEABLE = 0x02,
     VF_REMOVABLE  = 0x0f