Document that the Charset constructor coerces its argument to lower
case.
diff --git a/Doc/lib/emailcharsets.tex b/Doc/lib/emailcharsets.tex
index d1ae728..d654ada 100644
--- a/Doc/lib/emailcharsets.tex
+++ b/Doc/lib/emailcharsets.tex
@@ -23,10 +23,11 @@
when used in email headers or bodies. Certain character sets must be
converted outright, and are not allowed in email.
-Optional \var{input_charset} is as described below. After being alias
-normalized it is also used as a lookup into the registry of character
-sets to find out the header encoding, body encoding, and output
-conversion codec to be used for the character set. For example, if
+Optional \var{input_charset} is as described below; it is always
+coerced to lower case. After being alias normalized it is also used
+as a lookup into the registry of character sets to find out the header
+encoding, body encoding, and output conversion codec to be used for
+the character set. For example, if
\var{input_charset} is \code{iso-8859-1}, then headers and bodies will
be encoded using quoted-printable and no output conversion codec is
necessary. If \var{input_charset} is \code{euc-jp}, then headers will