Document that get_content_charset() coerces its return value to lower
case.
diff --git a/Doc/lib/emailmessage.tex b/Doc/lib/emailmessage.tex
index bfd8664..34c152d 100644
--- a/Doc/lib/emailmessage.tex
+++ b/Doc/lib/emailmessage.tex
@@ -443,8 +443,9 @@
\begin{methoddesc}[Message]{get_content_charset}{\optional{failobj}}
Return the \code{charset} parameter of the \mailheader{Content-Type}
-header. If there is no \mailheader{Content-Type} header, or if that
-header has no \code{charset} parameter, \var{failobj} is returned.
+header, coerced to lower case. If there is no
+\mailheader{Content-Type} header, or if that header has no
+\code{charset} parameter, \var{failobj} is returned.
Note that this method differs from \method{get_charset()} which
returns the \class{Charset} instance for the default encoding of the