Index: Doc/library/difflib.rst
===================================================================
--- Doc/library/difflib.rst	(revision 83064)
+++ Doc/library/difflib.rst	(working copy)
@@ -37,6 +37,10 @@
    complicated way on how many elements the sequences have in common; best case
    time is linear.
 
+   **Heuristic:** To speed-up matching, items that appear more than 1% of the time 
+   in sequences of at least 200 items are treated as junk. This has the unfortunate 
+   side-effect of giving bad results for sequences constructed from a small set of 
+   items. An option to turn off the heuristic will be added to a future version.
 
 .. class:: Differ