That is reasonable. I will follow your suggestion. Something like
this?
\edef\XeTeXVersionNumber{{\expandafter\@gobble\XeTeXrevision}
\ifnum\XeTeXVersionNumber<99992
<old xetex code>
\else
<new xetex code>
\fi
Not sure about that snippet, but I usually use the more generic:
\ifdim\number\XeTeXversion\XeTeXrevision in<0.99992in
For five-digit revsion numbers, they are equivalent,
but if \XeTeXrevision will contain a digit more,
the latter code might fail in certain cases
due to rounding in TeX's fixed point arithmetic.
(See example below, which yields
"ifdim not less" and "ifnum less".)
\newcount\myversion\myversion=0
\edef\myrevision{.999991}
\ifdim\number\myversion\myrevision in < 0.999992 in
ifdim less\message{^^Jifdim less^^J}\else
ifdim not less\message{^^Jifdim not less^^J}\fi
\def\mygobble#1{}
\edef\myrevno{\expandafter\mygobble\myrevision}
\ifnum\myrevno < 999992
ifnum less\message{^^Jifnum less^^J}\else
ifnum not less\message{^^Jifnum not less^^J}\fi
best,
Stefan
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