"\x0a" is a perfectly valid escape sequence, but unfortunately "\x0ac"
is equivalent to "\xac", and not "\x0a" "c" as we might expect --- *any*
number of hexadecimal characters after the "\x" is accepted. This can be
hit pretty easily if a newline is present in a format string.
"\x{...}" syntax is only available as of C++23, so use octal format
instead; a maximum of 3 digits following the backslash is accepted.
The alternative would be to render every escape like `" "\x0a" "`, but
it seems more effort that way.
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