> I believe that \low ,\high \lohi must be used with care:
>
> \starttext
>
> {\ss  A\low{\ruledvtop{\hsize=5in\input tufte }}}
>
> \blank
>
> {\tt B\low{\ruledvtop{\hsize=5in\input knuth }}}
>
> \stoptext

it works without the \input.