\documentclass{article}
\input{test2e}

% Composites with ascii base.
\begin{document}

\def\tst{%
\zz a\zz b\zz c\zz d\zz e\zz f\zz g\zz h\zz i\zz j\zz k\zz l\zz m%
\zz n\zz o\zz p\zz q\zz r\zz s\zz t\zz u\zz v\zz w\zz x\zz y\zz z%
\zz A\zz B\zz C\zz D\zz E\zz F\zz G\zz H\zz I\zz J\zz K\zz L\zz M%
\zz N\zz O\zz P\zz Q\zz R\zz S\zz T\zz U\zz V\zz W\zz X\zz Y\zz Z}%

\def\dotest#1{\par
\typeout{TESTING \string#1}%
\let\zz#1%
\tst
\par}

a $x$ \textcommabelow{k}

\START

\dotest{\`}
\dotest{\'}
\dotest{\^}
\dotest{\~}
\dotest{\"}
\dotest{\H}
\dotest{\r}
\dotest{\v}
\dotest{\u}
\dotest{\=}
\dotest{\.}
\dotest{\b}
\dotest{\c}
\dotest{\d}
\dotest{\k}
\dotest{\^}
\dotest{\~}
\dotest{\textcommabelow}

\end{document}