comment added

mysys/tree.c

@@ -46,6 +46,16 @@
   Implemented by monty.
 */
 
+/*
+  NOTE:
+  tree->compare function should be ALWAYS called as
+    (*tree->compare)(custom_arg, ELEMENT_KEY(tree,element), key)
+  and not other way around, as
+    (*tree->compare)(custom_arg, key, ELEMENT_KEY(tree,element))
+
+  ft_boolean_search.c (at least) relies on that.
+*/
+
 #include "mysys_priv.h"
 #include <m_string.h>
 #include <my_tree.h>