\startbuffer[circles]
draw fullcircle scaled 1cm;
draw fullcircle scaled 1cm shifted (2cm,0);
dotlabel.top(“O”,origin);
\stopbuffer
\def\StartHide{\doifmode{hideSolution}{\starteffect[hidden]}}
\def\StopHide{\doifmode{hideSolution}{\stopeffect\blank[5cm]}}
%\enablemode[hideSolution]
\starttext
\framed[]{This is what I want:}
\framedtext[]{
\StartHide
\samplefile{knuth}
Overbar is not \overbar{hidden}.
{\processMPbuffer[circles]}
\StopHide
}
\stoptext