[XeTeX] latin-1 encoded characters in commented out parts trigger log warnings

Ross Moore ross.moore at mq.edu.au
Sun Feb 21 12:46:00 CET 2021

Hi David.

On 21 Feb 2021, at 10:12 pm, David Carlisle <d.p.carlisle at gmail.com<mailto:d.p.carlisle at gmail.com>> wrote:

I think that should be taken up with the xstring maintainers.

Is  xstring  intended for use with XeTeX ?
I suspect not.
But anyway, there are still issues with this.

(BTW, I wrote this before Jonathan Kew’s response.)

I don't think there is any reasonable way to say you can comment out parts of a file in a different encoding.

I’m not convinced that this ought to be correct for TeX-based software.

TeX (not necessarily XeTeX) has always operated as a finite-state machine.
It *should* be possible to say that this part is encoded as such-and-such,
and a later part encoded differently.

I fully understand that editor software external to TeX might well have difficulties
with files that mix encodings this way, but TeX itself has always been byte-based
and should remain that way.

A comment character is meant to be viewed as saying that:
 *everything else on this line is to be ignored*
– that’s the impression given by TeX documentation.

If it is the documentation that is incorrect, then it should certainly be clarified.

For XeTeX and this particular example, it’s probably just a matter of checking
that the non-UTF8 characters occur *after* a UTF-8  ‘%' , and not issuing
an error message under these conditions.
A warning, maybe, but not an error.

The file encoding specifies the byte stream interpretation before any tex tokenization
If the file can not be interpreted as utf-8 then it can't be interpreted at all.

Why not?
Why can you not have a macro — presumably best on a single line by itself –
that says what follows next is to be interpreted in a different way to what came previously?
Until the next switch that returns to UTF-8 or whatever?

If XeTeX is based on eTeX, then this should be possible in that setting.

Even replacing by U+FFFD
is being lenient.


On Sun, 21 Feb 2021 at 11:04, jfbu <jfbu at free.fr<mailto:jfbu at free.fr>> wrote:

consider this


and call it xexstring.tex

Then xelatex xexstring triggers 136 warnings of the type

Invalid UTF-8 byte or sequence at line 35 replaced by U+FFFD.

Looking at file


I see that this matches with use of latin-1 encoded characters in comments.

Notice that it is a not a user decision here to use a latin-1
encoded file.

In fact I encountered this in a file I was given where
xstring package was loaded by another package.





Dr Ross Moore
Department of Mathematics and Statistics
12 Wally’s Walk, Level 7, Room 734
Macquarie University, NSW 2109, Australia
T: +61 2 9850 8955  |  F: +61 2 9850 8114
M:+61 407 288 255  |  E: ross.moore at mq.edu.au<mailto:ross.moore at mq.edu.au>
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