Tweat how MML specifies the encoding of binary data

* lisp/gnus/mml.el (mml-parse-1): Use `data-encoding' to be
slightly less confusing than `content-transfer-encoding'.

* doc/misc/emacs-mime.texi (MML Definition): Document it.

* lisp/gnus/message.el (message-insert-screenshot): Adjust usage.

3 files changed, 14 insertions, 5 deletions

diff --git a/doc/misc/emacs-mime.texi b/doc/misc/emacs-mime.texi
index 974cc10458d..9180b4ec205 100644
--- a/doc/misc/emacs-mime.texi
+++ b/doc/misc/emacs-mime.texi
@@ -693,8 +693,17 @@ Valid values are @samp{inline} and @samp{attachment}
 
 @item encoding
 Valid values are @samp{7bit}, @samp{8bit}, @samp{quoted-printable} and
-@samp{base64} (@code{Content-Transfer-Encoding}). @xref{Charset
-Translation}.
+@samp{base64}.  @xref{Charset
+Translation}.  This parameter says what
+@code{Content-Transfer-Encoding} to use when sending the part, and is
+normally computed automatically.
+
+@item data-encoding
+This parameter says what encoding has been used on the data, and the
+data will be decoded before use.  Valid values are
+@samp{quoted-printable} and @samp{base64}.  This is useful when you
+have a part with binary data (for instance an image) inserted directly
+into the Message buffer inside the @samp{"<#part>...<#/part>"} tags.
 
 @item description
 A description of the part (@code{Content-Description}).
diff --git a/lisp/gnus/message.el b/lisp/gnus/message.el
index 6c0f9b5c9ba..819f3e41d3d 100644
--- a/lisp/gnus/message.el
+++ b/lisp/gnus/message.el
@@ -8709,7 +8709,7 @@ used to take the screenshot."
 		   :max-width (truncate (* (frame-pixel-width) 0.8))
 		   :max-height (truncate (* (frame-pixel-height) 0.8))
 		   :scale 1)
-     (format "<#part type=\"image/png\" disposition=inline content-transfer-encoding=base64 raw=t>\n%s\n<#/part>"
+     (format "<#part type=\"image/png\" disposition=inline data-encoding=base64 raw=t>\n%s\n<#/part>"
 	     ;; Get a base64 version of the image -- this avoids later
 	     ;; complications if we're auto-saving the buffer and
 	     ;; restoring from a file.
diff --git a/lisp/gnus/mml.el b/lisp/gnus/mml.el
index 1d348f3a6f0..ef8aa6ac019 100644
--- a/lisp/gnus/mml.el
+++ b/lisp/gnus/mml.el
@@ -298,12 +298,12 @@ part.  This is for the internal use, you should never modify the value.")
 	;; We have a part that already has a transfer encoding.  Undo
 	;; that so that we don't double-encode later.
 	(when (and raw
-		   (cdr (assq 'content-transfer-encoding tag)))
+		   (cdr (assq 'data-encoding tag)))
 	  (with-temp-buffer
 	    (set-buffer-multibyte nil)
 	    (insert contents)
 	    (mm-decode-content-transfer-encoding
-	     (intern (cdr (assq 'content-transfer-encoding tag)))
+	     (intern (cdr (assq 'data-encoding tag)))
 	     (cdr (assq 'type tag)))
 	    (setq contents (buffer-string))))
 	(when (and (not raw) (memq nil charsets))