diff --git a/Doc/library/stdtypes.rst b/Doc/library/stdtypes.rst
index 122ed00..9ad33f3 100644
--- a/Doc/library/stdtypes.rst
+++ b/Doc/library/stdtypes.rst
@@ -135,8 +135,10 @@ Comparisons
    operator: !=
    operator: is
    operator: is not
+   operator: in
+   operator: not in
 
-There are eight comparison operations in Python.  They all have the same
+There are ten comparison operations in Python.  They all have the same
 priority (which is higher than that of the Boolean operations).  Comparisons can
 be chained arbitrarily; for example, ``x < y <= z`` is equivalent to ``x < y and
 y <= z``, except that *y* is evaluated only once (but in both cases *z* is not
@@ -163,6 +165,10 @@ This table summarizes the comparison operations:
 +------------+-------------------------+
 | ``is not`` | negated object identity |
 +------------+-------------------------+
+| ``in``     | membership              |
+-------------+-------------------------+
+| ``not in`` | negated membership      |
++------------+-------------------------+
 
 .. index::
    pair: object; numeric
@@ -201,8 +207,9 @@ exception.
    operator: in
    operator: not in
 
-Two more operations with the same syntactic priority, :keyword:`in` and
-:keyword:`not in`, are supported only by sequence types (below).
+The operations :keyword:`in` and :keyword:`not in`, are supported by
+sequences, sets, mappings, and can be customized by any class which defines
+the :meth:`__contains__` method.
 
 
 .. _typesnumeric: