Hello all,
Here's another strange behavior I've encountered (or normal behavior
I've misunderstood):
Both XeTeX and LuaTeX extends the ^^ mechanism so that:
^^^^abcd accesses characters 0-65535;
^^^^^abcde accesses characters 0-1048575;
^^^^^^abcdef (where abcdef is at most 10ffff) accesses characters 0-1114111.
As an illustration:
%%%%
\def\shownumber#1{%
\count1=`#1
\immediate\write16{\the\count1}
}
\shownumber{^^^^ffff} % 65535
\shownumber{^^^^^fffff} % 1048575
\shownumber{^^^^^^10ffff} % 1114111
%%%%
Fine. Now I'm trying to understand how those rows of superscripts are
parsed. All engines (i.e. TeX and PDFTeX too) parse:
\shownumber{^^^^^ }
as "(^^^)(^^ )", i.e. <char 30> (^^^, i.e. ^ - 64), so "30" is sent to
the terminal, plus <char 96> (^^<space>, i.e. <space> + 64), i.e. `,
which is typeset. But if you remove the braces (and add numbers so the
space isn't replaced with an end-of-line, and for another reason
explained presently):
\shownumber^^^^^ 12345679
then all engines behave as before, plus they typeset the numbers, except
LuaTeX, which sends 94 to the terminal and typesets only "56789". With
\shownumber^^^^^^ 12345679
the same happens except only "6789" is typeset.
What I suppose is: LuaTeX sees the "^^^^^" sequence, so it takes the
next five characters (including the space); but too bad, they don't fit
hexadecimal notation (because of the space), so it discards them (hence
their disappearance) and for some strange reason analyses "^^^^^"
backward, i.e. "^^(^^^)" = "^^<char 30>" = "<char 94>". This does not
happen with braces because the argument ends and the ^^ replacement
occurs after that. As for the 6-^ version, it gobbles the next six
characters, and then ends up with <char 94> I don't know how.
Well, what's going wrong, LuaTeX, or my head?
Best,
Paul
