\starttext

\def\TestMe#1%
  {\placeformula
   \startformula
     #1{i}\quad#1{ii}\quad#1{ii}\quad#1{iii}\quad#1{iiii}\quad#1{iiiii}\quad#1{iiiiii}\quad
     #1{iiiiii}_a^b
   \stopformula}

\TestMe\overbrace
\TestMe\overparent
\TestMe\overbracket
\TestMe\overrightarrow
\TestMe\overbar

\TestMe\underbrace
\TestMe\underparent
\TestMe\underbracket
\TestMe\underrightarrow
\TestMe\underbar

\TestMe\doublebrace
\TestMe\doubleparent
\TestMe\doublebracket

\stoptext
