diff --git a/src/obiavl.h b/src/obiavl.h
index e468e76..925d1bd 100644
--- a/src/obiavl.h
+++ b/src/obiavl.h
@@ -377,7 +377,10 @@ index_t obi_avl_find(OBIDMS_avl_p avl, Obi_blob_p value);
  * @warning The blob recovered is mapped in memory.
  *
  * @param avl_group A pointer to the AVL tree.
- * @param index The index of the value in the data array.
+ * @param index The index of the value in the form of a 64-bit integer
+ *              with the 32 left-most bits coding for the index of the tree of
+ *              the group in which the value is stored, and the 32 right-most bits
+ *              coding for the index at which the value is stored in that AVL tree.
  *
  * @returns A pointer to the blob recovered.
  *
@@ -395,7 +398,10 @@ Obi_blob_p obi_avl_group_get(OBIDMS_avl_group_p avl_group, index_t idx);
  * @param avl_group A pointer to the AVL tree group.
  * @param value The blob to add in the AVL tree group.
  *
- * @returns The index of the value newly added in the AVL tree group.
+ * @returns The index of the value newly added in the AVL tree group, in the form of a
+ *          64-bit integer with the 32 left-most bits coding for the index of the tree
+ *          of the group in which the value is stored, and the 32 right-most bits
+ *          coding for the index at which the value is stored in that AVL tree.
  * @retval -1 if an error occurred.
  *
  * @since April 2016