merge heads
diff --git a/Doc/library/email.mime.rst b/Doc/library/email.mime.rst
index ae340f7..2ce4868 100644
--- a/Doc/library/email.mime.rst
+++ b/Doc/library/email.mime.rst
@@ -185,5 +185,15 @@
minor type and defaults to :mimetype:`plain`. *_charset* is the character
set of the text and is passed as a parameter to the
:class:`~email.mime.nonmultipart.MIMENonMultipart` constructor; it defaults
- to ``us-ascii``. No guessing or encoding is performed on the text data.
+ to ``us-ascii``.
+
+ Unless the ``_charset`` parameter is explicitly set to ``None``, the
+ MIMEText object created will have both a :mailheader:`Content-Type` header
+ with a ``charset`` parameter, and a :mailheader:`Content-Transfer-Endcoding`
+ header. This means that a subsequent ``set_payload`` call will not result
+ in an encoded payload, even if a charset is passed in the ``set_payload``
+ command. You can "reset" this behavior by deleting the
+ ``Content-Transfer-Encoding`` header, after which a ``set_payload`` call
+ will automatically encode the new payload (and add a new
+ :mailheader:`Content-Transfer-Encoding` header).