I wrote a simple function for *workaround*. Hope it helps.

(defun sgml-xml-auto-coding-function-utf (size)
  (let* ((selected-coding (sgml-xml-auto-coding-function size))
         (selected (symbol-name selected-coding))
         (current-coding buffer-file-coding-system)
         (current (symbol-name current-coding))
         )
    (if (and (string-match "^utf-" selected)
             (string-match "^utf-.+\\(-with-signature.*\\)" current))
        (if (string= selected (substring current 0 (length selected)))
            current-coding
          ;; current=utf-cc-xxxx; selected=utf-ss; new -> utf-ss-xxxx
          (let ((sig (match-string 1 current))
                new)
            (string-match "^utf-\\(.+\\)" selected)
            (setq new (match-string 1 selected))
            (setq new (intern (concat "utf-" new sig)))
            (if (coding-system-p new)
                new
              selected-coding
              )))
      selected-coding))
    )

On Fri, Mar 18, 2011 at 1:56 PM, LIN Sumang <linsumang@gmail.com> wrote:

> Hi,
>
> I am using Emacs 23.2.1. I think sgml-xml-auto-coding-function() should
> respect the *-with-signature-* coding.
>
> Consider the scenario below:
> 1. xml file with the signature \376\377 at beginning of the file and the
> first line is
> <?xml version="1.0" encoding="utf-16be"?>
> 2. edit this file and save it. sgml-xml-auto-coding-function will use the
> utf-16be to save the file.
> 3. open the file again, get messed.
>
> In this case sgml-xml-auto-coding-function() shouldn't change the coding
> and if it really need to change the coding, it should append the
> *-with-signature-* to the selected coding.
>
> sgml-html-meta-auto-coding-function() should have same problem.
>
>
>