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<p>Given —</p>
<p></p>
<blockquote type="cite"><tt>\catcode 9 = 9</tt>
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margin-right:0px; -qt-block-indent:0; text-indent:0px;
line-height:100%;">
<tt>\let ~ = \undefined</tt></p>
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<tt>^^I~</tt></p>
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<tt>\end</tt></p>
</blockquote>
why does XeTeX report <br>
<p></p>
<p></p>
<blockquote type="cite"><tt>This is XeTeX, Version 3.141592653-2.6-0.999993 (TeX Live 2021/W32TeX) (preloaded format=xetex)</tt>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px;
margin-right:0px; -qt-block-indent:0; text-indent:0px;">
<tt>restricted \write18 enabled.</tt></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px;
margin-right:0px; -qt-block-indent:0; text-indent:0px;">
<tt>entering extended mode</tt></p>
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margin-right:0px; -qt-block-indent:0; text-indent:0px;">
<tt>(./untitled-10.tex</tt></p>
<p style=" margin-top:0px; margin-bottom:0px; margin-left:0px;
margin-right:0px; -qt-block-indent:0; text-indent:0px;">
<tt>! Undefined control sequence.</tt></p>
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margin-right:0px; -qt-block-indent:0; text-indent:0px;">
<tt>l.3 ^^I~</tt></p>
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margin-right:0px; -qt-block-indent:0; text-indent:0px;">
</p>
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<tt>? </tt></p>
</blockquote>
<p></p>
<p>This output makes it appear that the offending control sequence is (or might be)
<tt>^^I~</tt>, whereas it is in fact simply <tt>~</tt>. Should not the ^^I have been ignored rather than reported, as per line 1 ? Note line 3 does not really contain
<tt>^^I~</tt> but rather <tt><tab>~</tt>, but as tabs cannot be reliably included in e-mail I represent them here as
<tt>^^I</tt>. The <tt>^^I</tt> in the transcript is genuine.<br>
<tt></tt></p>
<p>-- <br>
<i>Philip Taylor</i><br>
<br>
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