#16128: clarify that instances of user-defined classes compare equal with themselves.

Doc/glossary.rst

@@ -320,7 +320,8 @@ Glossary
       All of Python's immutable built-in objects are hashable, while no mutable
       containers (such as lists or dictionaries) are.  Objects which are
       instances of user-defined classes are hashable by default; they all
-      compare unequal, and their hash value is their :func:`id`.
+      compare unequal (except with themselves), and their hash value is their
+      :func:`id`.
 
    IDLE
       An Integrated Development Environment for Python.  IDLE is a basic editor