\def\:temp#1{%
   {\m@th\ensuremath{_{\mbox{\fontsize\sf@size\z@#1}}}}}
\ifx \@textsubscript\:temp
  \def\:tempc#1{{\m@th%
     \ifmmode {\HCode{}}\sb {\mbox{\fontsize\sf@size\z@#1}}%
     \else%
        \a:textsubscript%
           {\mbox{#1}}\b:textsubscript%
     \fi }}
  \HLet\@textsubscript\:tempc
\fi
\NewConfigure{textsubscript}{2}
\Configure{textsubscript}
   {$\relax{\HCode{}}\sb}
   {$}
\Hinput{subscript}
\endinput

