[bug#67841] [PATCH] Clarify error messages for misuse of m4_warn and --help for -W.

    "All possible characters have a UTF-8 representation so this function 
    [encode_utf8] cannot fail."

What about non-characters, i.e., byte sequences that are invalid UTF-8?

What I found was that using \N{...} implies a Unicode string. From the
charnames(3) man page (stranged not named "perlcharnames"):

     Otherwise, any string that includes a "\N{charname}" or "\N{U+code
     point}" will automatically have Unicode rules (see "Byte and
     Character Semantics" in perlunicode).

Maybe pack("C") somehow can get to the bytes from a Unicode string?

Sorry I don't have time to experiment more. Must go look at the
first bug reports from the pretest ... --thanks, karl.