The following command ‘\def\@textsuperscript#1{% {\m@th\ensuremath{^{\mbox{\fontsize\sf@size\z@#1}}}}}’, where the exponent is too early to be an active character.
<..latex ltfloat..>+
\def\:temp#1{%
{\m@th\ensuremath{^{\mbox{\fontsize\sf@size\z@#1}}}}}
\ifx \@textsuperscript\:temp
\def\:tempc#1{{\m@th
\ifmmode {\HCode{}}\sp {\mbox{\fontsize\sf@size\z@#1}}%
\else
\a:textsuperscript
{\mbox{#1}}\b:textsuperscript
\fi }}
\HLet\@textsuperscript\:tempc
\fi
\NewConfigure{textsuperscript}{2}
\Configure{textsuperscript}
{$\relax{\HCode{}}\sp}
{$}
-_-_-
The definition of ‘\@textsuperscript’ in latex2e uses feartures not available in latex209.