diff --git a/Doc/library/email.message.rst b/Doc/library/email.message.rst
index 58f708c..c0aea5f 100644
--- a/Doc/library/email.message.rst
+++ b/Doc/library/email.message.rst
@@ -131,7 +131,11 @@ Here are the methods of the :class:`Message` class:
 
       Return ``True`` if the message's payload is a list of sub-\
       :class:`Message` objects, otherwise return ``False``.  When
-      :meth:`is_multipart` returns ``False``, the payload should be a string object.
+      :meth:`is_multipart` returns ``False``, the payload should be a string
+      object. Although if :meth:`is_multipart` does return ``True``, it does
+      not mean "msg.get_content_maintype() == 'multipart'" will return
+      the same answer. (An example would be when the :class:`Message` is of
+      type ``message/rfc822``)
 
 
    .. method:: set_unixfrom(unixfrom)
@@ -589,6 +593,7 @@ Here are the methods of the :class:`Message` class:
             >>> from email import message_from_binary_file
             >>> with open('Lib/test/test_email/data/msg_16.txt', 'rb') as f:
             ...     msg = message_from_binary_file(f)
+            >>> from email.iterators import _structure
 
        .. doctest::
 
@@ -605,6 +610,29 @@ Here are the methods of the :class:`Message` class:
    :class:`Message` objects can also optionally contain two instance attributes,
    which can be used when generating the plain text of a MIME message.
 
+   This method iterates over the subparts of any part where :meth:`is_multipart`
+   returns ``True`` even though ``msg.get_content_maintype() == 'multipart'``
+   returns ``False``. Here is an example showing that:
+
+       .. doctest::
+
+            >>> for part in msg.walk():
+            ...     print(part.get_content_maintype() == 'multipart')
+            True
+            False
+            False
+            False
+            False
+            False
+            False
+            >>> _structure(msg)
+            multipart/report
+                text/plain
+            message/delivery-status
+                text/plain
+                text/plain
+            message/rfc822
+                text/plain
 
    .. attribute:: preamble