On 2013–07–18 Alan Bowen wrote:

> Should the definition not be
>   \define[1]\anios{{\tfx \inmagin{#1}}}
> …………………………\inmargin….?

\inmagin would do the job with Knuth's new iTeX¹ system² but it's
not yet available in ConTeXt, which still uses legacy TeX. In the
near future it's unlikely that iTeX will be merged with ConTeXt,
although it's on the agenda for LuaTeX 2.0 ;)

Marco

¹ ring ring
² It has built-in spell check and is of interpreting unknown
  commands based on the context, so \inmagin would work just fine.