--- a/include/splay-tree.h	Thu Oct 25 07:37:49 2018 +0900
+++ b/include/splay-tree.h	Thu Feb 13 11:34:05 2020 +0900
@@ -1,5 +1,5 @@
 /* A splay-tree datatype.  
-   Copyright (C) 1998-2018 Free Software Foundation, Inc.
+   Copyright (C) 1998-2020 Free Software Foundation, Inc.
    Contributed by Mark Mitchell (mark@markmitchell.com).
 
    This file is part of GCC.
@@ -58,11 +58,18 @@
 typedef int (*splay_tree_compare_fn) (splay_tree_key, splay_tree_key);
 
 /* The type of a function used to deallocate any resources associated
-   with the key.  */
+   with the key.  If you provide this function, the splay tree
+   will take the ownership of the memory of the splay_tree_key arg
+   of splay_tree_insert.  This function is called to release the keys
+   present in the tree when calling splay_tree_delete or splay_tree_remove.
+   If splay_tree_insert is called with a key equal to a key already
+   present in the tree, the old key and old value will be released.  */
 typedef void (*splay_tree_delete_key_fn) (splay_tree_key);
 
 /* The type of a function used to deallocate any resources associated
-   with the value.  */
+   with the value.  If you provide this function, the memory of the
+   splay_tree_value arg of splay_tree_insert is managed similarly to
+   the splay_tree_key memory: see splay_tree_delete_key_fn.  */
 typedef void (*splay_tree_delete_value_fn) (splay_tree_value);
 
 /* The type of a function used to iterate over the tree.  */