> Fabrice Couvreur <mailto:fabrice1.couvreur@gmail.com>
> 10. August 2015 09:13
> Dear Hans,
> I tested without understanding what \unexpanded, and of course it works!
>
You can use ConTeXt’s \define command where you don’t have to think 
about \unexpanded etc., e.g.

\define[2]\ChapterCommand
   {\setbox\scratchbox\hbox to \leftmarginwidth{#1\hss}%
    \hskip-\dimexpr\leftmarginwidth+\leftmargindistance\relax
    \framed
      [background=titled,frame=off,offset=0pt]
      {\box\scratchbox
       \hskip\leftmargindistance
       #2}}

Wolfgang