<context source=yes>
\setuppapersize[A5]
\defdefine[2]\MyChapterCommand#1#2%
{\framed[frame=off,bottomframe=on,topframe=on]
{\vbox{\headtext{chapter} #1\blank#2}}}
\setupheadtext[chapter=Chapter]
\chapter[title={My First Chapter}]
</context>
This fails with the error message:
system > tex > error on line 9 in file test.tex: Emergency stop ...
===Exercise numbers===