Re: `write-region' writes different bytes than passed to it?

[Eli Zaretskii <eliz@gnu.org>]

> From: Philipp Stephani <p.stephani2@gmail.com>
> Date: Tue, 11 Dec 2018 13:30:07 +0100
> 
> usually `write-region' uses the coding system bound to
> `coding-system-for-write'. However, I've found a case where this
> doesn't seem to be the case:
> 
> $ emacs -Q -batch -eval '(let ((coding-system-for-write (quote
> utf-8-unix))) (write-region "\xC1\xB2" nil "/tmp/test.txt"))' && hd
> /tmp/test.txt
> 00000000  f2                                                |.|
> 00000001
> 
> That is, instead of the byte sequence C1 B2 it writes the single byte
> F2, which is an invalid UTF-8 sequence. Is that expected?

Yes, because "\xC1\xB2" just happens to be the internal multibyte
representation of a raw-byte F2.  Raw bytes are always converted to
their single-byte values on output, regardless of the encoding you
request.