On 16/04/2023 17:16, Philip Taylor (RHBNC) wrote:
Given —
\catcode 9 = 9
\let ~ = \undefined
^^I~
\end
why does XeTeX report
This is XeTeX, Version 3.141592653-2.6-0.999993 (TeX Live 2021/W32TeX)
(preloaded format=xetex)
restricted \write18 enabled.
entering extended mode
(./untitled-10.tex
! Undefined control sequence.
l.3 ^^I~
?
This output makes it appear that the offending control sequence is (or
might be) ^^I~, whereas it is in fact simply ~. Should not the ^^I have
been ignored rather than reported, as per line 1 ? Note line 3 does not
really contain ^^I~ but rather <tab>~, but as tabs cannot be reliably
included in e-mail I represent them here as ^^I. The ^^I in the
transcript is genuine.
First note: I see the same result with plain TeX. So not a XeTeX issue.
Anyway, this is expected behavior. The ^^I isn't part of the offending
control sequence; it's just the preceding context on the line, which is
what normally appears in a TeX error message.
Perhaps this is clearer if you add some more surrounding text:
\catcode 9 = 9
\let ~ = \undefined
abc^^I~def
\end
results in
(./x.tex
! Undefined control sequence.
l.3 abc^^I~
def
?
Ignored characters are not "removed from the input" (despite anything
Eijkhout says); they're still present, just ignored.
JK
