Merged revisions 77412 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk

........
  r77412 | r.david.murray | 2010-01-10 12:41:28 -0500 (Sun, 10 Jan 2010) | 3 lines

  Issue #7119: document that a program-generated Message object
  tree may be mutated when serialized.
........
diff --git a/Doc/library/email.mime.rst b/Doc/library/email.mime.rst
index 703110a..9cd94d8 100644
--- a/Doc/library/email.mime.rst
+++ b/Doc/library/email.mime.rst
@@ -69,7 +69,8 @@
    also be added.
 
    Optional *boundary* is the multipart boundary string.  When ``None`` (the
-   default), the boundary is calculated when needed.
+   default), the boundary is calculated when needed (for example, when the
+   message is serialized).
 
    *_subparts* is a sequence of initial subparts for the payload.  It must be
    possible to convert this sequence to a list.  You can always attach new subparts