paolobrasolin/antex

\setuppagenumbering[location={}]

\newbox\snippet
\setbox\snippet=\hbox{nope}

\newdimen\oneem
\oneem=1em
\newdimen\oneex
\oneex=1ex

\newwrite\metrics
\immediate\openout\metrics=\jobname.yml
\immediate\write\metrics{ex: \the\oneex}
\immediate\write\metrics{em: \the\oneem}
\immediate\write\metrics{ht: \the\ht\snippet}
\immediate\write\metrics{dp: \the\dp\snippet}
\immediate\write\metrics{wd: \the\wd\snippet}
\immediate\closeout\metrics

\starttext

\box\snippet

\hbox{nope}

\setbox\snippet=\hbox{nope}

\box\snippet

nope

\stoptext
%\starttext\box\snippet\stoptext