prettytok-test.tex

\documentclass{article}
\usepackage{prettytok}

\prettyN{123{4 5}\6}
\prettyN{#&^_:}
\edef\mytest{\prettyeN{\error}}

\prettyN {very long long long long long long long long long long long long long long argument \argument\argument\test123456}
\prettyeN {very long long long long long long long long long long long long long long argument \argument\argument\test123456}

\ExplSyntaxOn
\pretty:n {#&^_:}
\ExplSyntaxOff

\begin {document}
\prettyW abc \prettystop
\end {document}