\documentclass{article}
\begin{document}

This file contains a number of error
\begin{undefined-env}
Undefined environment
\end{undefined-env}

\catcode`^^ab=11 \catcode`^^bb=11

Now we have \fooa\foob\fooc\food\fooe %\w\+
We have also \^^abok^^bb\^^^^20ac!

\end{document}
