tree DOC minor enhancements

Fixes #550
diff --git a/src/tree_data.h b/src/tree_data.h
index a7e74ee..e5c46ee 100644
--- a/src/tree_data.h
+++ b/src/tree_data.h
@@ -162,7 +162,8 @@
  * ::lyd_node_leaf_list or ::lyd_node_anydata structures. This structure fits only to #LYS_CONTAINER, #LYS_LIST and
  * #LYS_CHOICE values.
  *
- * To traverse through all the child elements or attributes, use #LY_TREE_FOR or #LY_TREE_FOR_SAFE macro.
+ * To traverse all the child elements or attributes, use #LY_TREE_FOR or #LY_TREE_FOR_SAFE macro. To traverse
+ * the whole subtree, use #LY_TREE_DFS_BEGIN macro.
  */
 struct lyd_node {
     struct lys_node *schema;         /**< pointer to the schema definition of this node */
diff --git a/src/tree_schema.h b/src/tree_schema.h
index 8008f02..2a8bdfb 100644
--- a/src/tree_schema.h
+++ b/src/tree_schema.h
@@ -265,10 +265,10 @@
  *
  * @{
  */
-#define LYS_OUTOPT_TREE_RFC        0x01 /**< Conform to the RFC TODO tree output */
-#define LYS_OUTOPT_TREE_GROUPING   0x02 /**< Print groupings separately */
-#define LYS_OUTOPT_TREE_USES       0x04 /**< Print only uses instead the resolved grouping nodes */
-#define LYS_OUTOPT_TREE_NO_LEAFREF 0x08 /**< Do not print the target of leafrefs */
+#define LYS_OUTOPT_TREE_RFC        0x01 /**< Conform to the RFC TODO tree output (only for tree format) */
+#define LYS_OUTOPT_TREE_GROUPING   0x02 /**< Print groupings separately (only for tree format) */
+#define LYS_OUTOPT_TREE_USES       0x04 /**< Print only uses instead the resolved grouping nodes (only for tree format) */
+#define LYS_OUTOPT_TREE_NO_LEAFREF 0x08 /**< Do not print the target of leafrefs (only for tree format) */
 
 /**
  * @}
@@ -1218,7 +1218,8 @@
  * the node in some way or get more appropriate information, you are supposed to cast it to the appropriate
  * lys_node_* structure according to the #nodetype value.
  *
- * To traverse through all the child elements, use #LY_TREE_FOR or #LY_TREE_FOR_SAFE macro.
+ * To traverse through all the child elements, use #LY_TREE_FOR or #LY_TREE_FOR_SAFE macro. To traverse
+ * the whole subtree, use #LY_TREE_DFS_BEGIN macro.
  *
  * To cover all possible schema nodes, the ::lys_node type is used in ::lyd_node#schema for referencing schema
  * definition for a specific data node instance.
@@ -1246,7 +1247,10 @@
 
     LYS_NODE nodetype;               /**< type of the node (mandatory) */
     struct lys_node *parent;         /**< pointer to the parent node, NULL in case of a top level node */
-    struct lys_node *child;          /**< pointer to the first child node */
+    struct lys_node *child;          /**< pointer to the first child node \note Since other lys_node_*
+                                          structures represent end nodes, this member
+                                          is replaced in those structures. Therefore, be careful with accessing
+                                          this member without having information about the ::lys_node#nodetype. */
     struct lys_node *next;           /**< pointer to the next sibling node (NULL if there is no one) */
     struct lys_node *prev;           /**< pointer to the previous sibling node \note Note that this pointer is
                                           never NULL. If there is no sibling node, pointer points to the node